Question

Many pharmaceutical compounds contain amine functional groups, as they are adapted from amine-containing alkaloids. These drugs may be administered as the ‘free amine’ or as the ammonium salt (almost always HCl). Can you find a drug which has an amine functional group? Is it sold as the free amine or the HCl salt? Can you guess why it might be sold as that formulation? What might be the advantage of processing and administering the HCl salt over the free amine? What might be the advantage of processing and administering the free amine over the HCl salt?

Answer 1

Benadryl is Diphenhydramine hydrochloride. It is an antihistamine (it blocks histamine). It is used for allergy, hay fever and common cold.   
Benadryl is not sold as free amine. It is sold as HCl salt.

The advantage of processing and administering the HCl salt over the free amine is increase in water solubility.
Water soluble drugs are effective orally as they can be transported through blood. Free amines are water insluble whereas hydrochloride salts of amines are water soluble.

The advantage of processing and administering the free amine over the HCl salt is that the HCl salt might have lesser rate of dissolution in gastric fluids.