Re: why are many medicines 'something-zine HCl'?

You are correct about one function of the -HCl (Hydrochloride) added to many drugs: it makes them more soluble in water. Almost all drugs are organic chemicals, which are not readily soluble in water, however, most drugs contain nitrogen or oxygen atoms which make the chemical either basic or acidic. By titrating basic chemicals with hydrochloric acid (HCl) to form a neutral salt, a positive charge is added to the chemical which makes it water soluble. Similarly, titrating acidic chemicals with sodium hydroxide (NaOH) to form a neutral salt adds a negative charge to the chemical making it more soluble.

(basic chemical)B + HCl --> B-H⁺ + Cl^-

(acidic chemical)A-H +NaOH --> A^- + Na⁺ + H₂O

This neutralization is also important for making drugs that are strongly acidic or strongly alkaline more palatable. In the case of injected or I.V. drugs, it is crucial that the solution containing the drugs have a pH around 7.4, so that the surrounding tissue isn't unduly damaged.

In general, organic compounds are basic because of one or more amine (-NH₃) groups, so these chemicals have an "ine" ending, and their salts would be something"ine-HCl". Conversely, organic compounds that are acidic usually contain one or more carboxyl (-COOH) groups, and are called something"ic acid". Their salts then become "Sodium" something"ate". The reason there are more something"ine-HCl"'s than "Sodium" something"ate"'s has to do with the origins of the drugs. Many of the pharmaceutical chemicals used today are derivatives of alkaloids produced by medicinal plants, originally intended to keep away predators, but found to have curative properties in humans.