What is Codeine?
Codeine is an opioid pain reliever prescribed to treat mild to moderate pain. It belongs to a class of drugs called opioids which are derived from the opium poppy. Codeine works by binding to opioid receptors in the brain to decrease the sensation of pain.
Chemical Structure and Properties
Chemically, Codeine is classified as an alkyl homologue of morphine. Its molecular formula is C18H21NO3 and molecular weight is 299.377 g/mol. Codeine has three phenolic hydroxyl groups that can be methylated, one of which is methylated in codeine. This structural alteration results in codeine having weaker opioid effects than morphine while also possessing additional metabolic pathways that lead to its active morphine metabolite.
Metabolism and Mechanism of Action
Upon oral administration, codeine is metabolized primarily in the liver by the cytochrome P450 enzyme CYP2D6. Approximately 10% of codeine is converted directly to its active metabolite morphine. The rest is converted to various other inactive metabolites that are excreted in urine. The conversion of codeine to morphine is variable depending on a person's CYP2D6 enzyme activity. Poor metabolizers will receive less analgesic effects from codeine compared to extensive metabolizers.
Morphine produced from codeine metabolism binds to mu-opioid receptors in the central nervous system. This elicits codeine's analgesic effects by inhibiting the transmission of pain signals from the peripheral nerves to the brain. Activation of mu-opioid receptors also induces relaxation and euphoria along with constipation, respiratory depression, nausea and others as side effects.
Medical Uses
Codeine is prescribed for the treatment of mild to moderate pain. Common indications include pain caused by injuries, surgeries, dental procedures, musculoskeletal disorders like arthritis. It may also be used for treating coughs, diarrhea, and as an antitussive agent. Codeine combinations with acetaminophen or aspirin are available over-the-counter for cough and cold symptoms relief.
Dosage and Administration
The standard oral dose of codeine for pain relief ranges from 15-60 mg every 4 hours as needed. The maximum recommended daily dose is 240 mg. Codeine is also available in combination with other medications like acetaminophen in fixed doses. Codeine containing cough syrups and elixirs have even lower doses ranging from 12-60 mg per 5-30 ml. Codeine should only be taken for as long as needed to control symptoms under a physician's supervision.
Adverse Reactions and Precautions
Some common side effects of codeine include nausea, vomiting, constipation, drowsiness, dizziness and itching. Since codeine gets converted to morphine, risks of morphine such as respiratory depression and addiction also apply. Codeine use requires caution in patients with severe liver or kidney disease, breathing problems like asthma and the elderly as these groups are at higher risk. Combining with alcohol or other CNS depressants greatly increases the risks and should be avoided. Codeine use during pregnancy also requires assessment of risks versus benefits.
Alternatives to Codeine
For mild pain that does not respond well to over-the-counter medications, alternatives to codeine include ibuprofen, naproxen and other NSAIDs. Tramadol is sometimes used as an alternative opioid painkiller with lower abuse potential than codeine. Acetaminophen combined with low doses of aspirin or opioid alternatives like tapentadol may provide pain relief without the risks of codeine. Herbal remedies like St. John's Wort, willow bark and ginger can help manage mild to moderate pain. Physiotherapy, exercise, heat/cold therapy and relaxation techniques also aid in relieving certain types of pain.
Codeine Abuse and Regulation
Codeine has the potential for misuse and abuse owing to its opioid properties. While codeine alone produces euphoria at high doses, in combination with alcohol and other CNS depressants it significantly increases the risks of overdose. The Drug Enforcement Agency in the United States classifies codeine under Schedule III of the Controlled Substances Act. Codeine containing medicines are only available by prescription to monitor appropriate usage and prevent abuse. However, diverted pharmaceutical opioids and recreational codeine abuse still occurs requiring strict regulatory oversight. Dependence and addiction are also serious concerns if codeine is misused long term without medical supervision. Overall, responsible use of codeine as directed by a doctor can help manage pain conditions while minimizing the abuse and overdose risks.
Codeine is one of the most commonly prescribed opioid painkillers worldwide for mild to moderate pain relief. A prodrug, codeine gets metabolized via CYP2D6 to the active morphine metabolite which binds mu-opioid receptors to suppress pain transmission. While generally safe and effective used as directed, codeine carries risks of abuse, dependence and side effects like respiratory depression that must be weighed. Non-pharmacological therapies and alternative medications exist as well for relieving pain without use of opioids when possible. Overall, medical supervision is important for proper usage of codeine to maximize benefits and minimize risks.
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