Pharmacology · single question

What is the mechanism of action of clonazepam?

It increases the DURATION of chloride channel opening at the GABA-A receptor
It enhances GABA-A receptor activity by increasing the FREQUENCY of chloride channel opening
It blocks GABA-A receptors, reducing chloride conductance
It inhibits acetylcholinesterase at the neuromuscular junction

Show answer and explanation

Correct answer: B. It enhances GABA-A receptor activity by increasing the FREQUENCY of chloride channel opening

A. Incorrect. Increasing the DURATION of channel opening is the mechanism of BARBITURATES (phenobarbital, thiopental). At high doses barbiturates can open the channel without GABA at all, which is why they have no ceiling effect and a far narrower therapeutic index. 'Barbi-DURATes, Fre-BENZ-y' is the standard mnemonic.
B. Correct. Clonazepam is a BENZODIAZEPINE. It binds an allosteric site on the GABA-A receptor and increases the FREQUENCY of chloride channel opening in response to GABA, hyperpolarising the neuron. Benzodiazepines are therefore positive allosteric modulators — they require GABA to be present, which is why they have a ceiling effect and a wider safety margin than barbiturates.
C. Incorrect. Blocking GABA-A would be pro-convulsant. Flumazenil is the competitive ANTAGONIST at the benzodiazepine site and is the reversal agent for oversedation.
D. Incorrect. That describes neostigmine and pyridostigmine — cholinesterase inhibitors used in myasthenia gravis and for reversal of non-depolarising neuromuscular blockade.

More Pharmacology practice questions