Sun28November0440PM 27

An intravenous induction agent is presented to you. It has the following characteristics:

A cyclohexanone ring with one chiral centre and is presented as a racemic mixture

Local anaesthetic properties.

Which of the following best describes its primary mechanism of action?

(Please select 1 option)

Non-competitive antagonist affecting Ca2+ channels This is the correct answer

Reversible competitive antagonist affecting Na+ channels Incorrect answer selected

Inverse agonist affecting Cl- channels

Agonist affecting Cl- channels

Irreversible competitive antagonist affecting Ca2+ channels

Explanation

The drug in question is ketamine. As an intravenous induction agent its structure and pharmacodynamic effects are unique. The molecule is based on a cyclohexanone ring (2-(O-chlorophenyl)-2-methylamino cylohexanone). Ketamine acts mainly on the brain and spinal cord but also has local anaesthetic properties.

It is primarily a non-competitive antagonist for the N-D-methyl-aspartate (NMDA) receptor affecting Ca2+ .channels. It also has local anaesthetic activity by affecting neuronal Na+ channels.

Ketamine produces a profound state of dissociative anaesthesia (profound amnesia and analgesia) and sedation.

An example of an irreversible competitive antagonist includes phenoxybenzamine, an alpha-1 adrenoreceptor antagonist. It forms a covalent bond with the receptor affecting calcium influx.

Benzodiazepines are agonists affecting chloride influx at the GABAA receptor.

Flumazenil is an inverse agonist affecting chloride influx at the GABAA receptor.

Ketamine is a cyclohexanone derivative that is a non-competitive antagonist affecting Ca2+ channels.

Answer Statistics

1

21%

2

53%

3

7%

4

16%

5

5%

Times answered: 259