Codeine

Codeine is a painkiller and antitussive (cough suppressant) from the group of opioids. Codeine is a so-called "prodrug". This means that codeine is first converted in the body to its active form, morphine. It is used for the symptomatic treatment of coughs and for pain management. Codeine is available by prescription only.

Codeine is often administered in the form of a cough syrup or as drops. It is also available for use as a painkiller in capsule or tablet form, often in combination with other painkillers such as paracetamol.

Pharmacodynamics

Codeine has analgesic and narcotic effects and also increases pain tolerance. It is centrally active as an opiate, binding to all 3 opioid receptors in the brain. These receptors are involved in pain transmission in the body. However, this analgesic effect stems mainly from its conversion to morphine in the liver. Codeine also suppresses the urge to cough and may slow intestinal motility.

Pharmacokinetics

Codeine is almost entirely absorbed through the gastrointestinal tract. Maximum concentration is reached after about 60 minutes, with protein binding of only about 7-25%. Only about 5-10% of the given dose is converted to analgesic morphine in the liver. The remainder is broken down to ineffective metabolites and excreted by the kidneys. The plasma half-life of codeine and its metabolites is approximately 3 hours.

Drug Interactions

Under no circumstances should codeine be taken together with other centrally depressant substances such as antidepressants, MAO inhibitors, neuroleptics, sedatives or alcohol. These may increase the effect and possibly lead to life-threatening side effects.

Signs of overdose include confusion, constipation, shallow breathing, nausea and vomiting. In severe poisoning, life-threatening symptoms such as respiratory failure may occur.

In animal models, codeine has shown fertility damaging properties. It should therefore only be taken in pregnancy if the benefits clearly outweigh the potential risk.

Codeine, like other opiates, can lead to dependence. It should therefore not be taken beyond the duration prescribed by the doctor.

Side effects

Possible adverse reactions include allergic reactions, pruritus, hypotension, nausea, vomiting, constipation, headache, drowsiness or sleep disturbance, and shortness of breath.

Toxicological Data

Oral LD50: 427 mg kg-1 (rat)