Dihydrocodeine

Dihydrocodeine, also called DHC, Drocode or DF-118, is a synthetic opioid analgesic prescribed for post-operative pain, severe dyspnea, or as an antitussive. It was developed in the early 1900s, and is similar in chemical structure, pharmacological activity, and potency as codeine. Although dihydrocodeine does have extremely active metabolites, in the form of dihydromorphine and dihydromorphine-6-glucuronide (100x more potent), these metabolites are produced in such small amount that they do not have clinically important effects.

Indications

Approved indication for dihydrocodeine is the management of moderate to moderately severe pain. It is usually formulated as tablets containing 30 to 32 mg with one tablet taken every 4-6 hours when necessary.

In the United States, the most common analgesic brands with DHC are: Panlor SS (32 mg), ZerLor (32 mg), Panlor DC (16 mg) and Synalgos DC (16 mg). These combination products also include paracetamol (acetaminophen) and caffeine. Aspirin is used in the case of Synalgos DC.

Dihydrocodeine is sometimes marketed in combination preparations with paracetamol as co-dydramol (BAN) to provide greater pain relief than either agent used singly (q.v. drug synergy).

Side effects

As with other opioids, tolerance and physical and psychological dependence develop with repeated dihydrocodeine use. All opioids can impair the mental and/or physical abilities required for the performance of potentially hazardous tasks such as driving or operating machinery if taken in large doses, but have the opposite effect in moderate doses.

Other side effects include giddiness and a sense of hyperactivity. As with all drugs, side effects depend on the person taking the medication. They can range in severity from mild to extreme, from headaches to difficulty breathing.

Regulation

In the USA, it is a DEA Schedule II substance, although preparations containing small amounts of dihydrocodeine are classified as Schedule III or Schedule V, depending on the concentration of dihydrocodeine relative to other active constituents, such as paracetamol (acetaminophen). This scheduling is similar to codeine's.

In the United Kingdom dihydrocodeine is a Class B drug; however, it is available over-the-counter in small amounts (less than 8mg), when combined with paracetamol (see co-dydramol). Illegal possession of dihydrocodeine can result in up to 5 years in prison and/or an unlimited fine.

Chemistry

From the point of view of the organic chemist, the removal of the double bond makes the structure much more stable. It is more resistant to metabolic attack (hence a duration of action of 6 hours rather than 4 for codeine). It is also more stable in acidic, high-temperature enviroments. Whereas converting codeine to morphine is a difficult and unrewarding task, dihydrocodeine can be converted to dihydromorphine with very high yields (over 95%). Dihydromorphine is widely used in Japan.

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