| 6. Identifying if a Drug is an Acid or a
Base A first key to understanding pharmaceutics forces us to
look once again at the representation of molecules. We do not need a structure to
guide us here, we can simply look at the name of the material. Many drugs are acids
or bases. A common question is this one: How do we determine if a drug (or any other
compound) is an acid or a base? Here are some hints that may help you decide.
| Concept: Naming molecules so that chemists can determine the structure at the
molecular level, unequivocally, is a difficult and patient task. The chemical world
includes nomenclature experts whose task is to develop the systems for accurate naming of chemical
compounds for the International Union of Pure and Appied Chemistry. |
Let's name some acids: hydrochloric, nitric,
sulfuric, acetic, boric, benzoic come to mind. Salts formed by a reaction with these
compounds are conjugate acids, so the compound that reacted with them must have been a
base, right? Let's name some CONJUGATE ACIDS of basic drugs:
| Base |
Salt/Conjugate Acid |
| Diphenhydramine |
Diphenhydramine HCL |
| Glucosamine |
Glucosamine sulfate |
| Epinephrine |
Epinephrine sulfate |
| Ephedrine |
Ephedrine HCl |
| Atropine |
Atropine sulfate |
| Tetracycline |
Tetracycline HCl |
Most of these drugs, as you can tell by their name,
are "amines", which means they are weak bases. So, diphenhydramine is a base,
and diphenhydramine HCl is its conjugate acid.
How about common bases? Some that come to mind include
sodium hydroxide, calcium hydroxide, and potassium hydroxide. Salts that result from
reactions with these agents are conjugate bases, so the component present in the initial
reaction MUST have been an acid! So we see the following examples of conjugate bases of
ACIDIC drugs:
| Acid |
Salt/Conjugate Base |
| Phenobarbital |
Sodium Phenobarbital |
| Naproxyn |
Sodium Naproxyn |
| Fenoprofen |
Fenoprofen Calcium |
| Penicillin G |
Penicillin G Potassium |
If you don't have any idea based on the clues given
in the name of the compound, try looking at the salt to see if it is an acid or a base. |
