Pharmacology - Sedatives (Practice)


This category consists of mostly questions regarding benzodiazepines and barbiturates, and requires you to know the differences between the two types of drugs in terms of mechanism of action, therapeutic actions and adverse side effects and toxicities. Here’s a capsule review:


  1. Examples: diazepam, chlordiazepoxide, etc.
  2. Mechanism of action: modulate the activity of the inhibitory neurotransmitter, GABA
  3. Advantages vs. barbs: less addiction potential, less profound CNS depression, larger therapeutic index, less respiratory depression
  4. Other points to remember: A) many BDZs form active metabolites; B) IV injection of diazepam can cause irritation such as thrombophlebitis due to the solvent the BDZ is dissolved in.


1. (a) question in occurrence about barbs is always regarding thiopental and redistribution. Remember, thiopental’s action is terminated by redistribution of the drug out of the brain-it enters the brain rapidly and exits rapidly, thus quick onset and short duration of action.

2. (b) question wants you to remember that barbs are not analgesic – this is usually in the form of a list of actions and they want you to indicate which is not true.

3. Questions about toxicity –

  1. Barbiturate overdose kills you because of respiratory depression
  2. Barbs are contraindicated in a patient with intermittent porphyria – barbs enhance porphyrin synthesis and thus will aggravate the disease