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From Wikipedia, the free encyclopedia

Codeine
Skeletal formula
Space-filling model
Clinical data
Synonyms3-Methylmorphine
AHFS/Drugs.comMonograph
MedlinePlusa682065
Pregnancy
category
  • AU: A
  • US: C (Risk not ruled out)
Dependence
liability
Medium
Routes of
administration
By mouth, rectal, subcutaneous injection, intramuscular injection
ATC code
Legal status
Legal status
  • AU: Schedule 4 (prescription only)(combination preparations); Schedule 8 (single ingredient preparations))
  • CA: Schedule I
  • DE: Prescription only (Anlage III for higher doses)
  • UK: Class B
  • US: Schedule II (alone); Schedule III-V (combined with other active substances)
Pharmacokinetic data
BioavailabilityOral: ~90%
MetabolismLiver: CYP2D6 (to morphine), CYP3A4 (to norcodeine), UGT2B7 (to 3- and 6-glucuronides of codeine, norcodeine, and morphine)[1]
MetabolitesMorphine
Norcodeine
• Others (e.g., conjugates)
Onset of action15–30 minutes[2]
Elimination half-life2.5–3 hours
Duration of action4–6 hours[2]
Identifiers
CAS Number
PubChem CID
IUPHAR/BPS
DrugBank
ChemSpider
UNII
KEGG
ChEBI
ChEMBL
ECHA InfoCard100.000.882 Edit this at Wikidata
Chemical and physical data
FormulaC18H21NO3
Molar mass299.364 g/mol
3D model (JSmol)
 ☒N☑Y (what is this?)  (verify)

Codeine is an opiate used to treat pain, as a cough medicine, and for diarrhea.[2][3] It is typically used to treat mild to moderate degrees of pain.[2] Greater benefit may occur when combined with paracetamol (acetaminophen) or a nonsteroidal anti-inflammatory drug (NSAID) such as aspirin or ibuprofen.[2] Evidence does not support its use for acute cough suppression in children or adults.[4][5] In Europe it is not recommended as a cough medicine in those under twelve years of age.[2] It is generally taken by mouth.[2] It typically starts working after half an hour with maximum effect at two hours.[2] The total duration of its effects last for about four to six hours.[2]

Common side effects include vomiting, constipation, itchiness, lightheadedness, and drowsiness.[2] Serious side effects may include breathing difficulties and addiction.[2] It is unclear if its use in pregnancy is safe.[2] Care should be used during breastfeeding as it may result in opiate toxicity in the baby.[2] Its use as of 2016 is not recommended in children.[6] Codeine works following being broken down by the liver into morphine.[2] How quickly this occurs depends on a person's genetics.[2]

Codeine was discovered in 1832 by Pierre Jean Robiquet.[7] In 2013 about 361,000 kilograms of codeine were produced while 249,000 kilograms were used.[8] This makes it the most commonly taken opiate.[8] It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system.[9] The wholesale cost in the developing world is between 0.04 and 0.29 USD per dose as of 2014.[10] In the United States it costs about one dollar a dose.[2] Codeine occurs naturally and makes up about 2% of opium.[7]

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  • ✪ Codeine: What You Need To Know
  • ✪ Codeine: A Fairly Pointless Drug

Transcription

Codeine is an opioid found naturally in Papaver somniferum, the opium poppy. Its name comes from "kodeia," a Greek word for "poppy head." It's somewhat misleading to call it an opioid, however. The drug almost exclusively functions as a prodrug for morphine and other active substances. Codeine is typically a controlled substance, but it may be available over-the-counter in certain preparations. Often it's combined with paracetamol or NSAIDs like ibuprofen. These combinations can provide additional pain relief, but they come with additional safety risks. Among the positive effects are analgesia, sedation, euphoria, anxiolysis, physical euphoria, and dreaminess. The negatives include respiratory depression, drowsiness, depression, nausea, vomiting, constipation, bradycardia, and dysphoria. In medical settings, codeine is mainly an analgesic, antitussive, and anti-diarrheal. Rarely does it actually make sense as a medication. For cough, codeine does nothing in a large portion of cases, despite its alleged antitussive properties being utilized for many decades. Neither codeine nor other opioids are recommended for cough associated with the common cold. And multiple controlled trials have found it's no better than placebo. The support for its antitussive properties primarily comes from animal models and from experiments with induced and chronic cough, NOT from cough associated with upper respiratory infection. There's reason to believe different kinds of cough are controlled through different pathways in the body. Codeine may be practically ineffective at the pathway relevant to most acute coughs. Even some research with COPD shows codeine may have little to no efficacy in other kinds of cough. Therefore, taking it as a cough medicine, usually doesn't make sense. In the case of children suffering from cough, an FDA advisory panel overwhelmingly recommended it be contraindicated for everyone under 18 years old. When it comes to pain, codeine does have some efficacy, but it's not what you'd expect. Primarily due to non-efficacy factors like widespread accessibility and its unjustifiably good reputation, codeine is a popular analgesic for minor and moderate pain. It can dull the sensation of pain to the extent that it becomes bearable or almost unnoticeable. As I noted in the beginning, codeine is essentially nothing more than a prodrug. Though there's some debate about this, it's most important metabolite appears to be morphine. As such, why give someone codeine when you can just give them morphine? Well, there really isn't a good answer to that question. Codeine rarely makes sense from an efficacy perspective. The evidence strongly suggests patients are better off receiving NSAIDs, paracetamol, and other opioids like oxycodone or morphine. NSAIDs and paracetamol can be fairly effective on their own and when used in combination. Adding codeine to the mix can somewhat improve their efficacy, but it can often be avoided. And since codeine is a hit-and-miss way of giving someone an opioid, it's best to avoid whenever possible. An interesting application of codeine is in narcolepsy, where it may reduce daytime sleepiness. This area hasn't been heavily explored, yet some evidence suggests it could be useful. In medical settings, constipation is one of the most problematic negatives and it necessitate the use of laxatives. Other negatives include drowsiness, dizziness, cognitive impairment, depression, nausea, and vomiting. Changes in respiration can sometimes be observed at doses near the medical range, but they don't typically become a problem until someone overdoses or if they have a co-occurring respiratory issue. The drug is also used, typically at higher doses, for recreational purposes. Like other opioids, it offers relaxation, reduced care for physical or emotional problems, euphoria, and a dreamy state that facilitates easily shifting into semi-awake dreams. The contentment, relaxation, and general sense of well-being offered by codeine has the potential to be quite addictive depending on the user. Physical euphoria is a common effect at higher doses, presenting as waves of pleasurable, warm sensations around the body. Your limbs may also feel heavy and a sense of floatiness can be present when moving around. The drug doesn't cause overwhelming sedation at common doses. As the dose increases, people can become significantly impaired and drowsy. Higher amounts are also connected with a somewhat dissociative state, where people feel disconnected from their surroundings, their problems, and even their body. People may experience memories and see dream-like scenarios in this state. Users report being still and laying down are ideal for experiencing the effects. The negatives include an unpleasant taste in the mouth, sweating, severe nausea, stomach cramps, vomiting, respiratory depression, facial flushing and swelling, and itchiness around the body. Itchiness is considered an especially notable and annoying effect at higher doses. Codeine may be combined with antihistamines like promethazine and diphenhydramine. This can increase the depressant activity, which could raise the chance of unconsciousness, but it may also reduce itching. It's very important to remember codeine products often have other drugs in them. Paracetamol is one example and is also one of the most important to avoid using high doses of. Though you also shouldn't take high doses of ibuprofen or aspirin. Unless you're using them for medical reasons, combination products should be avoided. It hasn't been fully investigated, but there seems to be a ceiling dose with codeine. For the average user, a single-dose ceiling is somewhere around 300 to 500 mg. The analgesic and recreational properties don't significantly increase beyond this point, yet the negative effects might. This could stem from a high occupancy of mu-opioid receptors by codeine, which limits the ability of morphine and other metabolites to provide the desired effects. Codeine is a naturally occurring methylated morphine derivative, specifically 3-methylmorphine. It's an alkaloid in the morphinan class and is found in opium at a concentration of .2 to .8%. Though it can be collected from opium, it is now synthesized from morphine. On its own, codeine is basically inactive. It's best viewed as a prodrug, with metabolism to morphine and codeine-6-glucuronide controlling its efficacy. Much of its activity is ultimately tied to the mu-opioid site, a G protein-coupled receptor located along ascending and descending pain transmission pathways. These receptors are found in the PAG, locus ceruleus, rostral ventromedial medulla, and substantia gelatinosa, among other areas, like the cerebral cortex, thalamus, and limbic system. Mu-opioid agonism provides analgesia, euphoria, respiratory depression, and sedation. Agonsim in the midbrain is thought to be the core mechanism behind analgesia and the activity of drugs like morphine ultimately leads to the activation of descending inhibitory neurons. Opioids can also directly inhibit pain transmission from the periphery. Codeine's Tmax is 60 minutes and it's half-life is 2 to 3 hours. A specific enzyme, CYP2D6, is very important in the pharmacology of codeine. It controls the metabolism of codeine to morphine. This process, though perhaps not accounting for all of codeine's activity, is important. CYP2D6 is highly polymorphic. Some people are poor metabolizers, so they get little to no morphine, while others are ultrarapid metabolizers, capable of more easily generating dangerous levels of morphine. Only a small portion, 5 to 10%, actually becomes morphine. The primary metabolite is codeine-6-glucuronide, which does seem to have its own analgesic effects. Yet codeine's minor metabolite, morphine, plays a crucial role in the overall activity of the drug. If you're a poor metabolizer, like 7 to 10% of Caucasians are, codeine may do almost nothing for you. And if you're an ultrarapid metabolizer, like 20 to 30% of those with African or Middle Eastern heritage, you could be at a greater risk of severe negative effects. If you have a normal CYP2D6 genotype, your phenotype can also change if you're taking other drugs. People on antidepressants like fluoxetine and paroxetine can become worse metabolizers of codeine, reducing its efficacy. Some drugs, like rifampicin and dexamethasone, will do the opposite, thereby leading to more morphine per dose. Outside of directly using codeine, you can be exposed to the drug in a couple ways. Poppy seeds do contain some morphine and codeine. So a few poppy seed bagels can lead to detectable opioid levels in your body, though not enough to provide effects. The other source is your own body. There are signs pointing to a mammalian biosynthetic pathway for codeine and morphine that's similar to the one in P. somniferum. It appears the biosynthesis could begin with L-tyrosine and codeine ends up functioning as a precursor to morphine. Studies have found codeine and morphine in the brains of rats and nonhuman primates. Whether or not endogenous codeine and morphine do anything in humans isn't known, but morphine could be another endogenous opioid. Codeine is taken orally at 15 to 60 mg every 4 to 6 hours in medical settings. Nonmedically, a light dose is 50 to 100 mg, a common dose is 100 to 150 mg, and a strong dose is 150 to 200 mg. Due to genetic factors, you should evaluate your response to a light dose before attempting larger amounts and it's wise to avoid using more than a common dose. Codeine technically has a very long history because of its presence in opium. P. somniferum may have been cultivated for opium around 3000 BC by the Sumerians living in today's Iraq. The referred to opium as "gil," meaning joy. And the poppy was called the "plant of joy." The Ebers Papyrus from 1500 BC Egypt included a "remedy to prevent [the] excessive crying of children." This remedy involved a poppy-sourced substance and would be given for 4 days, after which the crying would "stop at once." Remedies of this kind were considered dangerous due to the unreliable potency of opium preparations. Arab traders likely brought the drug to India and China in the 700s. And the Arabian system of medicine, including opium use, certainly spread to India by the 900s. From the 900s to 1200s, opium made its way from Asia Minor to all parts of Europe. Within a few centuries, manuscripts began to discuss the nonmedical use of opium and physical dependence in Turkey, Egypt, Germany, and England. After another few centuries, codeine was finally isolated from opium in 1832 by a French chemist. Throughout its history codeine has been a popular antitussive and it's also been treated as significantly safer than morphine. Neither of these reputations makes a lot of sense, so the history of codeine is that of a drug being used without much justification. Around 1900, codeine was thought to have a very low chance of fatal overdose. A report in JAMA said there were no fatalities in the literature. Though some reports of fatalities associated with the drug began to show up in the coming decades. This led a publication in 1937 to estimate codeine's lethal dose as 300 to 500 mg, though that paper eluded to people surviving larger amounts. A death was reported in 1932 and another was reported in 1943, involving a patient with acute asthma. There were also claims suggesting the drug was nonaddictive and had no real potential for physical dependence. Unsurprisingly, a test in 1934 confirmed codeine had morphine-like dependence potential. From the 1960s onward, it's continued to be used as an analgesic and antitussive in the West and around the world. Its recreational use started to receive more attention in the 60s and 70s. Publications like The Wall Street Journal described teenagers using codeine-containing cough syrups. A similar kind of use started in the 1990s, though this time it involved a combination of codeine, promethazine, soda, and candy. That combination, known as "purple drank" and "lean," spread outward from the Houston, Texas region in the early 1990s. Throughout its existence, purple drank has been associated with hip-hop and the African American community, with musicians like Lil Wayne bringing the drug into the spotlight. People seem to frequently underestimate the harm potential of codeine and codeine-centric combinations. At least two key figures in the Houston hip-hop community, Robert Davis Jr and Chad Butler, died from causes associated, in part, with purple drank. Reports from the early 2000s found up to 25% of at-risk youth in Houston had used codeine cough syrups, with 10% reporting use in the past 30 days. Other surveys near Houston and in other parts of the US suggest codeine and purple drank are fairly common drugs among young people. Interest in codeine has been driven by the media and by the music community. Some high-profile codeine-related arrests also increased interest. A former Green Bay Packer, Johnny Jolly, was arrested in 2008 for possessing 200 grams of codeine. Two years later, former Oakland Raiders Quarterback JaMarcus Russell was arrested for possession of codeine. And in 2011, ESPN did a special on purple drank and codeine, partly focusing on the the drug's apparent popularity among athletes. The use of codeine for nonmedical purposes exists well beyond the United States. Reports from India, South Africa, Ireland, and other countries have indicated codeine-containing products are at least a minor source of recreational drug use and addiction. Since the 1990s there's been a pushback against codeine in the medical community. For example, the American Academy of Pediatrics said in 1997 that there's no good evidence supporting codeine as an antitussive in children. That didn't actually prevent it from being used as such, unfortunately. Many papers have called for codeine to no longer be treated as a first-line analgesic, to rarely be used in children, and to not be recommended as an antitussive. But changing prescribing practices isn't easy. There has been some traction at least when it comes to minimizing its use in young children. Due to a lack of clear efficacy and the existence of accidental deaths, the World Health Organization, the FDA, The European Medicines Agency, and Health Canada have all taken a stricter stance towards codeine. Some hospitals have largely moved away from codeine products, particularly in children, instead choosing to administer NSAIDs, paracetamol, and alternative opioids. Despite all this, codeine prescribing to children barely changed in the US from 2001 to 2010. And in 2011, the FDA reported 1.7 million children ha d a codeine prescription filled at a pharmacy. Some of the most frequent prescribing comes from otorhinolaryngologists. Yet, the American Academy of Otolaryngology-Head and Neck Surgery determined the negatives of codeine outweighed its utility for adenotonsillectomy patients. As you can see, the modern history of codeine often involves physicians prescribing codeine even though the leaders in the field recommend against its use. Other frequent prescribers are dentists, pediatricians, emergency department physicians, and general physicians. US poison control centers reported over 900 codeine-associated poisonings in children 12 and older in 2011. An additional 1400 poisonings were reported with analgesics or cough and cold preparations containing codeine. Codeine was the most frequently prescribed opioid in children in 2013. When physicians have been pushed to use morphine in place of codeine, they've sometimes been hesitant. A 2013 survey in the UK found doctors appeared to view the switch to morphine negatively, yet not necessarily with good justification. As we move forward, the push to largely abandon codeine will continue, but it's unlikely we will see the end of codeine any time soon. In the US, codeine is a Schedule 2 drug. Certain polysubstance formulations are Schedule 3 or 5. And there are some over-the-counter products containing codeine with other drugs. A similar regulatory framework is seen around the world. Australia, Canada, and the UK all treat codeine as a controlled drug. Yet low-concentration preparations featuring multiple substances can be purchased over-the-counter or without a physician's prescription. There have been calls in those countries to change this framework, so we could see more restrictive policies in the coming years. Australia has already decided to eliminate non-prescription codeine beginning in 2018. Codeine is relatively safe at common and medical doses. An overdose can come with respiratory depression, coma, and vomit aspiration. It may also be somewhat more likely to produce seizure activity, delirium, mania, and other psychological symptoms than other opioids. Though the seizure activity could just be coming from hypoxia. Death, while rare, occurs via respiratory depression. Ultrarapid metabolizers are at a much higher risk of fatal overdose and severe respiratory depression, along with every other overdose symptom. This issue has received a lot of attention in the context of breastfeeding women and young children. There have been instances of severe respiratory depression and death from medical doses in children. Outside of breastfeeding exposure, which has sometimes caused problems, issues seem to be more common after adenoidectomy or adenotonsillectomy. Kids undergoing those procedures may also have obstructive sleep apnea, raising the chance of hypoxia when they're given codeine. It's best to avoid codeine in those cases. Physical dependence to codeine is entirely possible and its severity is determined by dose and how long you've been using. Withdrawal can range from moderate flu-like symptoms to a significantly more uncomfortable state. Insomnia, restlessness, runny nose, stomach pain, diarrhea, and chills are common. Craving for the drug is also much higher. Acute psychiatric problems beyond depression and low mood are rare, but they have occurred. Some people appear susceptible, especially in overdose, to psychotic states, mania, and other issues. Morphine isn't the only opioid associated with these psychiatric changes, so there appears to be some connection between the opioid system and problematic psychiatric conditions. Chronic use might raise the risk of depression, sometimes mediated by androgen deficiency, which occurs in a large portion of chronic users. Some of the risky combinations include other depressants, like ethanol, other opioids, dissociatives, benzodiazepines, pregabalin, and GHB. If you have any questions, feel free to put them in the comments. You can also email me. The Drug Classroom is exclusively funded by donations. Listeners like you make TDC possible. If you want to support, you can do so through Patreon, PayPal, or Bitcoin.

Contents

Medical uses

Codeine is used to treat mild to moderate pain and to relieve cough.[2] Codeine is also used to treat diarrhea and diarrhea-predominant irritable bowel syndrome, although loperamide (which is available without a prescription for milder diarrhea), diphenoxylate, paregoric or even laudanum are more frequently used to treat severe diarrhea.[11]

There is weak evidence that it is useful in cancer pain but it is associated with increased side effects.[12] The American Academy of Pediatrics does not recommend its use in children due to side effects.[6] The FDA lists age under 12 years old as a contraindication to use.[13]

Furthermore, codeine has been found as an endogenous compound, along with morphine, in the brains of non-human primates with depolarized neurons, indicating that codeine may function as a neurotransmitter or neuromodulator in the central nervous system.[14]

Cough

Evidence does not support its use for acute cough suppression in children or adults.[15][5] In Europe it is not recommended as a cough medicine in those under twelve years of age.[2] There is some tentative evidence it can reduce a chronic cough in adults.[16]

Formulations

Codeine is marketed as both a single-ingredient drug and in combination preparations with paracetamol (as co-codamol: e.g., brands Paracod, Panadeine, and the Tylenol-with-codeine series, including Tylenol 3 and 1,2,4); with aspirin (as co-codaprin); or with ibuprofen (as Nurofen Plus). These combinations provide greater pain relief than either agent alone (drug synergy).

Codeine is also commonly marketed in products containing codeine with other pain killers or muscle relaxers, as well as codeine mixed with phenacetin (Emprazil with codeine No. 1, 2, 3, 4 and 5), naproxen, indomethacin, diclofenac, and others, as well as more complex mixtures, including such mixtures as aspirin + paracetamol + codeine ± caffeine ± antihistamines and other agents, such as those mentioned above.

Codeine-only products can be obtained with a prescription as a time release tablet. Codeine is also marketed in cough syrups with zero to a half-dozen other active ingredients, and a linctus (e.g., Paveral) for all of the uses for which codeine is indicated.

Injectable codeine is available for subcutaneous or intramuscular injection only; intravenous injection is contraindicated as this can result in non-immune mast-cell degranulation and resulting anaphylactoid reaction. Codeine suppositories are also marketed in some countries.

Side effects

Common adverse effects associated with the use of codeine include drowsiness and constipation. Less common are itching, nausea, vomiting, dry mouth, miosis, orthostatic hypotension, urinary retention, euphoria, dysphoria, and coughing. Rare adverse effects include anaphylaxis, seizure, acute pancreatitis, and respiratory depression.[17] As with all opiates, longer-term effects can vary, but can include diminished libido, apathy, and memory loss. Some people may have allergic reactions to codeine, such as the swelling of skin and rashes.[2]

Tolerance to many of the effects of codeine, including its therapeutic effects, develops with prolonged use. This occurs at different rates for different effects, with tolerance to the constipation-inducing effects developing particularly slowly for instance.

A potentially serious adverse drug reaction, as with other opioids, is respiratory depression. This depression is dose-related and is a mechanism for the potentially fatal consequences of overdose. As codeine is metabolized to morphine, morphine can be passed through breast milk in potentially lethal amounts, fatally depressing the respiration of a breastfed baby.[18][19] In August 2012, the United States Federal Drug Administration issued a warning about deaths in pediatric patients < 6 years old after ingesting "normal" doses of paracetamol with codeine after tonsillectomy; this warning was upgraded to a black box warning in February 2013.[20]

Some patients are very effective converters of codeine to its active form, morphine, resulting in lethal blood levels. The FDA is presently recommending very cautious use of codeine in young tonsillectomy patients: use the drug in the lowest amount that can control the pain, use "as needed" and not "around the clock", and seek immediate medical attention if a child on codeine exhibits excessive sedation or abnormally noisy breathing.

Withdrawal and dependence

As with other opiate-based pain killers, chronic use of codeine can cause physical dependence. When physical dependence has developed, withdrawal symptoms may occur if a person suddenly stops the medication. Withdrawal symptoms include: drug craving, runny nose, yawning, sweating, insomnia, weakness, stomach cramps, nausea, vomiting, diarrhea, muscle spasms, chills, irritability, and pain. To minimize withdrawal symptoms, long-term users should gradually reduce their codeine medication under the supervision of a healthcare professional.[21]

There is also no evidence that CYP2D6 inhibition is useful in treating codeine dependence,[22] though the metabolism of codeine to morphine (and hence further metabolism to glucuronide morphine conjugates) does have an effect on the abuse potential of codeine.[23] However, CYP2D6 has been implicated in the toxicity and death of neonates when codeine is administered to lactating mothers, particularly those with increased 2D6 activity ("ultra-rapid" metabolizers).[19][24]

Pharmacology

Pharmacodynamics

Codeine (and metabolite) at opioid receptors
Compound Affinities (Ki) Ratio Ref
MOR DOR KOR MOR:DOR:KOR
Codeine 79 nM >1,000 nM >1,000 nM ND [25]
Morphine 1.8 nM 90 nM 317 nM 1:50:176 [26]

Equianalgesic doses[27][28][29]
Compound Route Dose
Codeine PO 200 mg
Hydrocodone PO 20–30 mg
Hydromorphone PO 7.5 mg
Hydromorphone IV 1.5 mg
Morphine PO 30 mg
Morphine IV 10 mg
Oxycodone PO 20 mg
Oxycodone IV 10 mg
Oxymorphone PO 10 mg
Oxymorphone IV 1 mg

Codeine is an opioid.[30] It is a selective agonist of the μ-opioid receptor (MOR).[30] Codeine itself has relatively weak affinity for the MOR.[30][25] Instead of acting directly on the MOR, codeine functions as a prodrug of its major active metabolite morphine, which is a far more potent MOR agonist in comparison.[30][26]

Pharmacokinetics

The conversion of codeine to morphine occurs in the liver and is catalyzed by the cytochrome P450 enzyme CYP2D6.[31] CYP3A4 produces norcodeine and UGT2B7 conjugates codeine, norcodeine, and morphine to the corresponding 3- and 6- glucuronides. Srinivasan, Wielbo and Tebbett speculate that codeine-6-glucuronide is responsible for a large percentage of the analgesia of codeine, and, thus, these patients should experience some analgesia.[32] Many of the adverse effects will still be experienced in poor metabolizers. Conversely, 0.5-2% of the population are "extensive metabolizers"; multiple copies of the gene for 2D6 produce high levels of CYP2D6 and will metabolize drugs through that pathway more quickly than others.

Some medications are CYP2D6 inhibitors and reduce or even completely block the conversion of codeine to morphine. The most well-known of these are two of the selective serotonin reuptake inhibitors, paroxetine (Paxil) and fluoxetine (Prozac) as well as the antihistamine diphenhydramine (Benadryl), and the antidepressant bupropion (Wellbutrin, also known as Zyban). Other drugs, such as rifampicin and dexamethasone, induce CYP450 isozymes and thus increase the conversion rate.

CYP2D6 converts codeine into morphine, which then undergoes glucuronidation. Life-threatening intoxication, including respiratory depression requiring intubation, can develop over a matter of days in patients who have multiple functional alleles of CYP2D6, resulting in ultra-rapid metabolism of opioids such as codeine into morphine.[33][34][35]

Studies on codeine's analgesic effect are consistent with the idea that metabolism by CYP2D6 to morphine is important, but some studies show no major differences between those who are poor metabolizers and extensive metabolizers. Evidence supporting the hypothesis that ultrarapid metabolizers may get greater analgesia from codeine due to increased morphine formation is limited to case reports.[36]

Due to increased metabolism of codeine to morphine, ultrarapid metabolizers (those possessing more than 2 functional copies of the CYP2D6 allele) are at increased risk of adverse drug effects related to morphine toxicity. Guidelines released by the Clinical Pharmacogenomics Implementation Consortium (CPIC) advise against administering codeine to ultrarapid metabolizers, where this genetic information is available. The CPIC also suggests that codeine use be avoided in poor metabolizers, due to its lack of efficacy in this group.[37]

Codeine and its salts are readily absorbed from the gastrointestinal tract and ingestion of codeine phosphate produces peak plasma concentrations in about one hour. Plasma half life is between 3 and 4 hours and oral/intramuscular analgesic potency ratio is approximately equal to 1:1.5. The most common conversion ratio, given on equianalgesia charts used in the United States, Canada, the UK, Republic of Ireland, the European Union, Russia and elsewhere as 130 mg IM equals 200 mg PO—both of which are equivalent to 10 mg of morphine sulphate IV and 60 mg of morphine sulphate PO. The salt:freebase ratio of the salts of both drugs in use are roughly equivalent, and do not generally make a clinical difference.[38]

Codeine is metabolised by O- and N-demethylation in the liver to morphine and norcodeine. Codeine and its metabolites are excreted almost entirely by the kidney, mainly as conjugates with glucuronic acid.[39]

The active metabolites of codeine, notably morphine, exert their effects by binding to and activating the μ-opioid receptor.

Chemistry

Relation to other opioids

Codeine has been used in the past as the starting material and prototype of a large class of mainly mild to moderately strong opioids; such as hydrocodone (1920 in Germany), oxycodone (1916 in Germany), dihydrocodeine (1908 in Germany), and its derivatives such as nicocodeine (1956 in Austria).[citation needed] However, these opioids are no longer synthesized from codeine and are usually synthesized from other opium alkaloids; specifically thebaine.[citation needed] Other series of codeine derivatives include isocodeine and its derivatives, which were developed in Germany starting around 1920. In general, the various classes of morphine derivatives such as ketones, semisynthetics like dihydromorphine, halogeno-morphides, esters, ethers, and others have codeine, dihydrocodeine, and isocodeine analogues.[40] The codeine ester acetylcodeine is a common active impurity in street heroin as some codeine tends to dissolve with the morphine when it is extracted from opium in underground heroin and morphine base labs.

As an analgesic, codeine compares weakly to other opiates. Related to codeine in other ways are codoxime, thebacon, codeine-N-oxide (genocodeine), related to the nitrogen morphine derivatives as is codeine methobromide, and heterocodeine, which is a drug six times stronger than morphine and 72 times stronger than codeine due to a small re-arrangement of the molecule, viz. moving the methyl group from the 3 to the 6 position on the morphine carbon skeleton.

Drugs bearing resemblance to codeine in effects due to close structural relationship are variations on the methyl groups at the 3 position including ethylmorphine a.k.a. codethyline (Dionine) and benzylmorphine (Peronine). While having no narcotic effects of its own, the important opioid precursor thebaine differs from codeine only slightly in structure. Pseudocodeine and some other similar alkaloids not currently used in medicine are found in trace amounts in opium as well.

History

Codeine, or 3-methylmorphine, is an alkaloid found in the opium poppy, Papaver somniferum var. album, a plant in the papaveraceae family. Opium poppy has been cultivated and utilized throughout human history for a variety of medicinal (analgesic, anti-tussive and anti-diarrheal) and hypnotic properties linked to the diversity of its active components, which include morphine, codeine and papaverine.

Codeine is found in concentrations of 1% to 3% in opium prepared by the latex method from unripe pods of Papaver somniferum. The name codeine is derived from the Ancient Greek κώδεια (kṓdeia, "poppy head"). The relative proportion of codeine to morphine, the most common opium alkaloid at 4% to 23%, tends to be somewhat higher in the poppy straw method of preparing opium alkaloids.

Until the beginning of the 19th century, raw opium was used in diverse preparations known as laudanum (see Thomas de Quincey's Confessions of an English Opium-Eater, 1821) and paregoric elixirs, a number of which were popular in England since the beginning of the 18th century; the original preparation seems to have been elaborated in Leiden, the Netherlands around 1715 by a chemist named Lemort; in 1721 the London Pharmacopoeia mentions an Elixir Asthmaticum, replaced by the term Elixir Paregoricum ("pain soother") in 1746.

The progressive isolation of opium's several active components opened the path to improved selectivity and safety of the opiates-based pharmacopeia.

Morphine had already been isolated in Germany by Friedrich Sertürner in 1804.[41] Codeine was first isolated in 1832 in France by Pierre Robiquet, already famous for the discovery of alizarin, the most widespread red dye, while working on refined morphine extraction processes.[42] Robiquet is also credited with discovering caffeine independently of Pelletier, Caventou, and Runge.[42] This paved the way for the elaboration of a new generation of safer, codeine-based specific antitussive and antidiarrheal formulations.

Codeine is the most widely used opiate in the world,[43][44] and is one of the most commonly used drugs overall according to numerous reports by organizations including the World Health Organization and its League of Nations predecessor agency. It is one of the most effective orally administered opioid analgesics and has a wide safety margin. Its strength ranges from 8% to 12% of morphine in most people; differences in metabolism can change this figure as can other medications, depending on its route of administration.

While codeine can be directly extracted from opium, its original source, most codeine is synthesized from the much more abundant morphine through the process of O-methylation,[44][45] through a process first completed in the late 20th century by Robert C. Corcoran and Junning Ma.[46]

By 1972, the effects of the War On Drugs had caused widespread shortages of illicit and licit opiates because of a scarcity of natural opium, poppy straw, and other sources of opium alkaloids, and the geopolitical situation was growing difficult for the United States. After much of the opium and morphine in the US National Stockpile of Strategic & Critical Materials was tapped in order to ease severe shortages of medicinal opiates — the codeine-based antitussives in particular — in late 1973, researchers were tasked with finding a way to synthesize codeine and its derivatives. They quickly succeeded using petroleum or coal tar and a process developed at the United States' National Institutes of Health.

Numerous codeine salts have been prepared since the drug was discovered. The most commonly used are the hydrochloride (freebase conversion ratio 0.805), phosphate (0.736), sulphate (0.859), and citrate (0.842). Others include a salicylate NSAID, codeine salicylate (0.686), a bromide (codeine methylbromide, 0.759), and at least four codeine-based barbiturates, the cyclohexenylethylbarbiturate (0.559), cyclopentenylallylbarbiturate (0.561), diallylbarbiturate (0.561), and diethylbarbiturate (0.619). The latter was introduced as Codeonal in 1912, indicated for pain with nervousness.[47] Codeine methylbromide is also considered a separate drug for various purposes.[48]

Codeine and morphine, as well as opium, were used in an attempt to treat diabetes in the 1880s and thereafter, as recently as the 1950s.[49]

Society and culture

Names

It is often sold as a salt in the form of either codeine sulfate or codeine phosphate in the United States, United Kingdom and Australia. Codeine hydrochloride is more common worldwide and the citrate, hydroiodide, hydrobromide, tartrate, and other salts are also seen.[50] The chemical name for codeine is morphinan-6-ol, 7,8-didehydro-4,5-epoxy-3-methoxy-17-methyl-, (5α,6α)-[51]

Recreational use

A heroin (diamorphine) or other opiate/opioid addict may use codeine to ward off the effects of withdrawal during periods where their preferred drug is unavailable or unaffordable.[52]

Codeine is also available in conjunction with the anti-nausea medication promethazine in the form of a syrup. Brand named as Phenergan with Codeine or in generic form as promethazine with codeine. In the 1990s it started to be mixed with soft drinks to be used as a recreational drug and was called 'syrup', 'lean', or 'purple drank'.[53] Rapper Pimp C, from the group UGK, died from an overdose of this combination.[54]

Codeine is used in illegal drug laboratories to make morphine.[55][56]

Detection

Codeine and its major metabolites may be quantitated in blood, plasma or urine to monitor therapy, confirm a diagnosis of poisoning or assist in a medico-legal death investigation. Drug abuse screening programs generally test urine, hair, sweat or saliva. Many commercial opiate screening tests directed at morphine cross-react appreciably with codeine and its metabolites, but chromatographic techniques can easily distinguish codeine from other opiates and opioids. It is important to note that codeine usage results in significant amounts of morphine as an excretion product. Furthermore, heroin contains codeine (or acetyl codeine) as an impurity and its use will result in excretion of small amounts of codeine. Poppy seed foods represent yet another source of low levels of codeine in one's biofluids. Blood or plasma codeine concentrations are typically in the 50–300 µg/L range in persons taking the drug therapeutically, 700–7000 µg/L in chronic users and 1000–10,000 µg/L in cases of acute fatal over dosage.[57][58][59]

Codeine is produced in the human body along the same biosynthetic pathway as morphine.[31] Urinary concentrations of endogenous codeine and morphine have been found to significantly increase in individuals taking L-DOPA for the treatment of Parkinson's disease.[31]

Legal status

Around the world, codeine is, contingent on its concentration, a Schedule II and III drug under the Single Convention on Narcotic Drugs.[60] In Australia, Canada, New Zealand, Sweden, the United Kingdom, the United States and many other countries, codeine is regulated under various narcotic control laws. In some countries it is available without a medical prescription in combination preparations from licensed pharmacists in doses up to 20 mg, or 30 mg when sold combined with 500 mg paracetamol.

Australia

In Australia, Since February 1, 2018, preparations containing codeine are not available without a prescription.[61]

Preparations containing pure codeine (e.g., codeine phosphate tablets or codeine phosphate linctus) are available on prescription and are considered S8 (Schedule 8, or "Controlled Drug Possession without authority illegal"). Schedule 8 preparations are subject to the strictest regulation of all medications available to consumers.

Canada

In Canada tablets containing 8 mg of codeine combined with 15 mg of caffeine and 300 mg of acetaminophen are sold as T1s (Tylenol Number 1) without a prescription. A similar tablet called "A.C. & C." (which stands for Acetylsalicylic acid with Caffeine and Codeine) containing 325–375 mg of acetylsalicylic acid (Aspirin) instead of acetaminophen is also available without a prescription. Both tablets are kept behind the counter and must be dispensed by a pharmacist who may limit quantities. Names of many codeine and dihydrocodeine products in Canada tend to follow the narcotic content number system (Tylenol With Codeine No. 1, 2, 3, 4 &c) mentioned below in the section on the United States; it came to be in its current form with the Pure Food & Drug Act of 1906.

Codeine became a prescription-only medication in the province of Manitoba on February 1, 2016. A pharmacist may issue a prescription, and all purchases are logged to a central database to prevent overprescribing.[62]

Denmark

In Denmark codeine is sold over the counter in dosages up to 9.6 mg (with aspirin, brand name Kodimagnyl); anything stronger requires a prescription.[63]

France

In France, before 2017 most preparations containing codeine did not require a doctor's prescription. Example products containing codeine include Néocodion (codeine and camphor), Tussipax (ethylmorphine and codeine), Paderyl (codeine alone), Codoliprane (codeine with paracetamol), Prontalgine and Migralgine (codeine, paracetamol and caffeine).[64] In 2017 the law was changed making mandatory a prescription for all codeine products along with ethylmorphine and dextromethorphan [65]

Germany, Switzerland, and Austria

Codeine is listed under the Betäubungsmittelgesetz in Germany and the similarly named narcotics and controlled substances law in Switzerland. In Austria, the drug is listed under the Suchtmittelgesetz in categories corresponding to their classification under the Single Convention on Narcotic Drugs. Dispensing of products containing codeine and similar drugs (dihydrocodeine, nicocodeine, benzylmorphine, ethylmorphine etc.), in general, requires a prescription order from a doctor or the discretion of the pharmacist.

Municipal and provincial regulations may impact availability, in particular in Austria and Switzerland, which allows cities and provinces to regulate the selling of the least-regulated schedule of the SMG/BtMG. Individual chemists' shops can opt out of providing them or imposing volume, frequency, or single-purchase limitations and other things of the same store. Plain codeine hydrochloride tablets as well as other non-injectable forms of codeine and its midrange derivatives can be dispensed in this way; the same goes for most chemical classes of benzodiazepines, the majority of non-barbiturate sedative/hypnotics, and at least a handful of barbiturates.

Title 76 of the Schengen treaty has made it possible for countries within the signatory states to import and export drugs with various provisos, recording and ordering requirements, and various other rules.

Greece

Codeine is classed as an illegal drug in Greece, and individuals possessing it could conceivably be arrested, even if they were legitimately prescribed it in another country. It is sold only with a doctor's prescription (Lonarid-N, Lonalgal).[66]

Hong Kong

In Hong Kong, codeine is regulated under Laws of Hong Kong, Dangerous Drugs Ordinance, Chapter 134, Schedule 1. It can be used legally only by health professionals and for university research purposes. The substance can be given by pharmacists under a prescription. Anyone who supplies the substance without prescription can be fined $10,000 (HKD). The maximum penalty for trafficking or manufacturing the substance is a $5,000,000 (HKD) fine and life imprisonment. Possession of the substance for consumption without license from the Department of Health is illegal with a $1,000,000 (HKD) fine and/or 7 years of jail time.

However, codeine is available without prescription from licensed pharmacists in doses up to 0.1% [67]:Schedule 1, Part IV, paragraph 23 (i.e. 5 mg/5ml)[67]:Section 3, (1) (a)

India

Codeine preparations require a prescription in India. A preparation of paracetamol and codeine is available in India. Codeine is also present in various cough syrups as codeine phosphate including chlorpheniramine maleate. Pure codeine is also available as codeine sulphate tablets. Codeine containing cough medicine has been banned in India with effect from 14 March 2016. The Ministry of Health and Family Welfare has found no proof of its efficacy against cough control.[68]

Iran

Preparations of codeine in Iran normally comes with paracetamol or guaifenesin, and can be purchased over-the-counter. Pure codeine is also available as codeine phosphate 30 mg tablets and special permit required to purchasing. Iran's deputy health minister reported that codeine combinations is Iran's best selling OTC medication.[citation needed]

Ireland

In Ireland, new regulations came into effect on 1 August 2010[69] concerning codeine, due to worries about the overuse of the drug. Codeine remains a semi non-prescriptive, over-the-counter drug up to a limit of 12.8 mg per pill, but codeine products must be out of the view of the public to facilitate the legislative requirement that these products "are not accessible to the public for self-selection".[70] In practice, this means customers must ask pharmacists for the product containing codeine in name, and the pharmacist makes a judgement whether it is suitable for the patient to be using codeine, and that patients are fully advised of the correct use of these products. Products containing more than 12.8 mg codeine are available on prescription only.[71]

Italy

Codeine tablets or preparations require a prescription in Italy. Preparations of paracetamol and codeine are available in Italy as Co-Efferalgan and Tachidol.

Japan

Low dose codeine is available over the counter at pharmacies but not higher doses.

Maldives

The Maldives takes an infamously strict line on medicines, with many common drugs, notably anything with containing codeine being banned unless you have a notarized and authenticated doctor's prescription. Visitors breaking the rules, even inadvertently, have been deported or imprisoned.

Nigeria

Nigeria in 2018 plans to ban the manufacture and import of cough syrup that include codeine as an ingredient.[72] This is due to concerns regarding its use to get intoxicated.[72]

Romania

Codeine is not allowed without a medical prescription. Codeine is sold under the name Farmacod and its concentration does not exceed 15 mg. There is a known combination of acetylsalicylic acid, paracetamol and codeine phosphate hemihydrate named Aspaco that is allowed without a medical prescription but its case is signed with an exclamation red symbol which means that driving won't be allowed during treatment. There are no sanctions whether the drug is given without a prescription.

The Russian Federation

According to ITAR-Tass and Austria Presse-Agentur, OTC availability of codeine products was rescinded nationwide in 2012 because of the discovery of the Krokodil method of underground desomorphine synthesis. Opponents of the move point out that codeine has not been available OTC in 22 of Russia's oblasts for years and the demand will call forth its own supply, meaning that only legitimate end users are negatively impacted (activist quoted in Pravda story on issue).[citation needed]

South Africa

Codeine is available over the counter in South Africa. Certain pharmacies require people to write down their name and address to ensure they are not buying too much over a short period although many do not require this at all. According to Dr Lochan Naidoo, the former president of the National Narcotics Control Board, making the drugs more difficult to obtain could lead to even worse problems where people in withdrawal would turn to illicit drugs to get their fix.[73] Although codeine is freely available, South Africa has a fairly low annual prevalence rate of opiate use at 0.3% compared to the United States at 0.57% where all opiates are strictly regulated.

Sri Lanka

Codeine preparations are available as over the counter pharmacy medicines in Sri Lanka. The most common preparation is Panadeine, which contains 500 mg of Paracetamol and 8 mg of Codeine. But cough syrup containing Codeine is banned, even with a prescription.

United Arab Emirates

The UAE takes an exceptionally strict line on medicines, with many common drugs, notably anything containing codeine being banned unless one has a notarized and authenticated doctor's prescription. Visitors breaking the rules, even inadvertently, have been deported or imprisoned. The US Embassy to the UAE maintains an unofficial list of what may not be imported.

United Kingdom

In the United Kingdom, the sale and possession of codeine are restricted separately under law.

Neat codeine and higher-strength codeine formulations are generally prescription-only medicines (POM) meaning that the sale of such products is restricted under the Medicines Act 1968. Lower-strength products containing combinations of up to 12.8 mg of codeine per dosage unit, combined with paracetamol, ibuprofen or aspirin are available over the counter at pharmacies. Codeine linctus of 15 mg per 5 ml is also available at some pharmacies, although a purchaser would have to request it specifically from the pharmacist.

Under the Misuse of Drugs Act 1971 codeine is a Class B controlled substance or a Class A drug when prepared for injection.[74] The possession of controlled substances without a prescription is a criminal offence.[75] However, certain preparations of codeine are exempt from this restriction under Schedule 5 of the Misuse of Drugs Regulations 2001. It is thus legal to possess codeine without a prescription, provided that it is compounded with at least one other active or inactive ingredient and that the dosage of each tablet, capsule, etc. does not exceed 100 mg or 2.5% concentration in the case of liquid preparations. The exemptions do not to apply to any preparation of codeine designed for injection.[76]

United States

In the United States, codeine is regulated by the Controlled Substances Act. Federal law dictates that codeine be a Schedule II controlled substance when used in products for pain-relief that contain codeine alone or more than 90 mg per dosage unit. Codeine without aspirin or acetaminophen (Tylenol) is very rarely available or prescribed in order to discourage abuse. Tablets of codeine in combination with aspirin or acetaminophen (paracetamol) and intended for pain relief are listed as Schedule III, allowing electronic fills and refills without a physical paper-copy of the physician ordered prescription.

Cough syrups are classed as Schedule III, IV or V, depending on formulation. For example, the acetamenophen/codeine antitussive liquid is a Schedule IV controlled substance.[77]

Some states have chosen to reclassify codeine preparations at a more restrictive schedule in order to lower the instances of its abuse. Minnesota, for instance, has chosen to reclassify Schedule V some codeine preparations (e.g. Cheratussin) as a Schedule II controlled substance.[78]

In some jurisdictions where codeine is a Schedule V substance, it is available as an antitussive liquid, combined with paracetamol, aspirin or terpin hydrate, in limited strengths and quantities without a prescription (at the discretion of the dispensing pharmacist). In most jurisdictions such sales are entered into a dispensed-narcotics database, requiring customer signature, to limit excessive use.

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