Which among the following is NOT a classification criterion of drugs?

Correct — A. Drugs are classified on four bases in the school chemistry syllabus: pharmacological effect, drug action, chemical structure and molecular targets.

A patient's behavioural condition is not on that list. It describes the person being treated, not the molecule or its site of action, so it cannot sort drugs into classes.

Each of the other three is a working classification used by a different professional. The odd one out is option (a).

Why the others are wrong

• (b)
  Molecular target — Molecular target is a genuine criterion. Drugs acting on the same biomolecule, such as a particular enzyme or receptor, are grouped together, and this is the classification medicinal chemists find most useful.
• (c)
  Pharmacological effect — Pharmacological effect groups drugs by the effect produced, so all analgesics sit together because they relieve pain, whatever their chemistry. It is the classification most useful to a prescribing doctor.
• (d)
  Chemical structure — Chemical structure groups drugs sharing a common structural skeleton, as the sulphonamides do. Members of such a group often, though not always, share a similar pharmacological activity.

Drugs are low molecular mass chemicals that interact with larger biomolecules such as enzymes and receptors, producing a biological response.

Because the same molecule can be described by its structure, by its target, by its action and by its effect, chemistry recognises several parallel classifications rather than one.

Each serves a different user. A doctor reaches for effect, a chemist for structure or target. The question tests whether you know the list, so a plausible-sounding clinical phrase is inserted to see if the list is memorised or merely half-remembered.

Key facts

• Drugs are classified on the basis of pharmacological effect, drug action, chemical structure and molecular targets.
• Classification by molecular target groups drugs acting on the same biomolecule and is the one most useful to medicinal chemists.
• Classification by chemical structure groups drugs with a common structural skeleton, such as the sulphonamides.
• Drugs are low molecular mass chemicals that interact with macromolecular targets such as enzymes and receptors.

Common traps

• Drug action is the fourth criterion and it is missing from these options, so the option list is not the full list.
• Behavioural condition sounds clinical and therefore plausible, which is exactly why it is the answer to a NOT question.
• Read the NOT in the stem before scanning the options, because three of these four are true statements about drug classification.

No directly related past PYQ was found.