Dimenhydrinate (marketed under brand names
Dramamine,
Gravol and Vertirosan) is an over-the-counter drug used to prevent motion sickness. It is closely related to diphenhydramine HCl, or
Benadryl. The differences relate to the weight-for-weight potency (50 mg dimenhydrinate contains 29 mg of the drug diphenhydramine), delay of action (dimenhydrinate must dissociate into diphenhydramine and its counterion in the body before it is active, therefore diphenhydramine produces effects sooner), and degree of sedation produced. Chemically, dimenhydrinate is a salt of two drugs: diphenhydramine and 8-chlorotheophylline, a chlorinated derivative of the
theophylline.
Theophylline is very closely related to
caffeine and theobromine, mild central nervous system stimulants. It was thought 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. In actuality, the sedation caused by diphenhydramine is substantially stronger than the stimulation caused by chlorotheophyllinate. Diphenhydramine, an ethanolamine-class antihistamine, is found in most OTC
sleep aids and allergy preparations, such as
Tylenol PM and
Benadryl. It is primarily a H1-antagonist, but also possesses an antimuscarinic effect. It is used in
Dramamine to prevent nausea and emesis; however, the development of the chemical
meclizine has overtaken its usage (marketed as "
Dramamine II") because
meclizine doesn't produce as much drowsiness.
-coppied from wikipedia
