Dimenhydrinate - Pharmacology

Pharmacology

The effects of dimenhydrinate are very similar to those of diphenhydramine. The main differences are a lower potency, and a longer latency. 50 mg dimenhydrinate contains 27.2 mg of diphenhydramine, so it is less potent at equal doses. Also, dimenhydrinate must dissociate into diphenhydramine and its counterion in the body before it is active, so it produces effects more slowly than diphenhydramine.

Theophylline was added in order to counteract drowsiness. Theophylline is very closely related to caffeine and theobromine, mild central nervous system stimulants. It was thought by scientists that by combining the antiemetic effects of diphenhydramine with a stimulant, the extreme drowsiness induced by the former could be mitigated somewhat by the latter. The sedation caused by diphenhydramine, however, is substantially stronger than the stimulation caused by chlorotheophylline, so the overall effect is still mostly sedating. While dimenhydrinate is still used to prevent nausea and emesis, the development of the chemical meclozine has overtaken its usage (marketed as "Dramamine II") because meclozine is less likely to cause drowsiness.