Tuesday, 30 October 2012

All are true about Clozapine except:

Option A: More potently block D2 compared to D1.
Option B: Blood level above 350 mg/ml associate with better response
Option C: Should not be used with Carbamazepine concurrently
Option D: Should be discontinued if the WBC count is below 3,000/mm3 cells

The correct answer is A.

More potently block D2 compared to D1. (Kaplan & Sadock synopsis of psychiatry, 10th edition, page 1095-1096)

  • Clozapine is an antagonist of 5-HT2A, D1, D3, D4, and alpha1 receptors. It has relatively low potency as a D2-receptor antagonist. Data from PET scanning show that 10 mg of haloperidol produces 80 percent occupancy of striatal D2 receptors, whereas clinically effective dosages of clozapine occupy only 40 to 50 percent of striatal D2 receptors. 
  • This difference in D2 receptor occupancy is probably why clozapine does not cause extrapyramidal adverse effects. 
  • It has also been postulated that clozapine, as well as other SDAs, bind more loosely to the D2 receptor, and as a result of this fast dissociation, more normal dopamine neurotransmission is possible. 

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