Astemizole
Astemizole (marketed under the brand name Hismanal, developmental code R43512) was a second-generation antihistamine drug that has a long duration of action. Astemizole was discovered by Janssen Pharmaceutica in 1977. It has been withdrawn from the market in most countries because of rare but potentially fatal side effects (QTc interval prolongation and related arrhythmias due to hERG channel blockade).
Diphenhydramine
Diphenhydramine is an antihistamine mainly used to treat allergies. It is also used for insomnia, symptoms of the common cold, tremor in parkinsonism, and nausea. It is used by mouth, injection into a vein, and injection into a muscle. Maximal effect is typically around two hours after a dose, and effects can last for up to seven hours.
Common side effects include sleepiness, poor coordination, and an upset stomach. Its use is not recommended in babies. There is no clear risk of harm when used during pregnancy; however, use during breastfeeding is not recommended. It is a first generation H-antihistamine and works by blocking certain effects of histamine. Diphenhydramine is also an anticholinergic.
Diphenhydramine was first made by George Rieveschl and came into commercial use in 1946. It is available as a generic medication. The wholesale price in the developing world is about per dose. In the United States, it costs less than for a typical month’s supply. It is sold under the trade name Benadryl, among others.