Meptazinol

Meptazinol is a centrally acting analgesic belonging to the hexahydroazepine series, which has demonstrated mixed agonist and antagonist activity at opioid receptors.

Receptor binding studies have shown that although meptazinol displays only a low affinity for δ and κ opioid receptor sites, it has a somewhat higher affinity for a subpopulation of μ sites. These binding sites also display a high affinity for the endogenous opioid peptides, and are thought to be responsible for, among other things, analgesia, but not for the mediation of respiratory depression.

A component of its analgesic action is also attributable, in mice at least, to an effect on central cholinergic transmission. In this respect it differs from all conventional analgesic drugs which have been examined.

After oral administration, meptazinol is rapidly absorbed and peak plasma levels are reached within 90 minutes. The plasma elimination half-life is variable (1.4-4 hours). The peak analgesic effect is seen within 30-60 minutes and lasts about 3-4 hours. The drug is rapidly metabolised to the glucronide, and mostly excreted in the urine.

After intramuscular administration, meptazinol is rapidly absorbed and peak plasma levels are reached within 30 minutes. The plasma half-life is approximately 2 hours. The peak analgesic effect is seen within 30-60 minutes and lasts about 3-4 hours.

After intravenous administration, the onset of action is immediate, occurring within minutes and lasts a minimum of one hour.

The major route of metabolism is via the glucuronidation pathway and excretion occurs mainly in the urine.

Standard toxicity tests revealed no unexpected findings of clinical significance.