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 It has been withdrawn from the market in most countries because of rare but potentially fatal side effects (QTc interval prolongation and related arrhythmias due to hERG channel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).
Hydroxyzine
Hydroxyzine, sold under the brand names Atarax among others, is a medication of the antihistamine type. It is used in the treatment of itchiness, anxiety, and nausea, including that due to motion sickness. It is used either by mouth or injection into a muscle.
Common side effects include sleepiness, headache, and a dry mouth. Serious side effects may include QT prolongation. It is unclear if use during pregnancy or breastfeeding is safe. Hydroxyzine works by blocking the effects of histamine. It is in the piperazine family of chemicals.
It was first made by Union Chimique Belge in 1956 and was approved for sale by Pfizer in the United States later that year. In the United Kingdom 28 doses cost less than a pound. In the United States the wholesale cost in 2018 was about 0.05 USD per dose. In the United States about 8 million prescriptions were written for hydroxyzine in 2016.