Dihydrocodeine

Dihydrocodeine is a semisynthetic opioid analgesic prescribed for pain or severe dyspnoea or as an antitussive, either alone or in combination with other analgesic agents. In addition to tablets, solutions, elixirs, and other oral dosage forms, dihydrocodeine is also available in some countries as an injectable solution for deep subcutaneous and intra-muscular administration. As with codeine, intravenous administration should be avoided as it can lead to anaphylaxis and life-threatening pulmonary oedema.

Pharmacodynamics

Dihydrocodeine is metabolized to dihydromorphine - a highly active metabolite with high affinity for μ-opioid receptors.

Pharmacokinetics

Bioavailability is low (approximately 20%) when administered orally. This is due to poor gastrointestinal absorption. Metabolized in the liver by CYP 2D6 to an active metabolite, dihydromorphine, and by CYP 3A4 to a secondary primary metabolite, nordihydrocodeine. Elimination occurs via the kidneys and excretion via the urine. The half-life is approximately 4 hours.

Drug interactions

Particular attention should be paid to drugs which are also degraded by or induce the enzyme CYP2D6. These may significantly influence plasma levels of dihydromorphine and lead to severe side effects. To a lesser extent, this also applies to drugs that interact with the CYP3A4 enzyme.

Side effects

As with other opioids, tolerance and physical and psychological dependence develop with repeated use of dihydrocodeine. All opioids, when taken in high doses, can impair mental or physical abilities needed to perform potentially dangerous tasks such as driving or operating machinery.

As with all medications, side effects depend on the person taking the medication. They can range in severity from mild to extreme, from headache or dry mouth to shortness of breath.

Constipation is a side effect common with dihydrocodeine and almost all other opioids. Itching and skin flushing and other blood vessel dilating effects are also common side effects.

Toxicological Data

LD50 (rat, oral): 359 mg-kg-.