What Medications Affect Clozapine Levels?

40 year old patient with history of schizophrenia stabilized on clozapine presented with recent worsening of psychotic symptoms. He recently started smoking and initiated treatment for GERD. Which drug-drug interaction is responsible this presentation?

Literature review done by Singh et al compared the list of medications interacting with clozapine and how this affect serum level changes in clozapine. The following table will summarize these findings:-

 

Medications Serum Clozapine Level CYP450
ANTIDEPRESSANTS
Fluvoxamine Increase in Clozapine level 1A2; 3A4
Paroxetine Increase in Clozapine level 2D6
Sertraline Increase in Clozapine level 1A2
 
ANTICONVULSANTS
Carbamazepine Decrease in Clozapine level Pan-Inducer
Valproic Acid Mixed Reports 1A2
 
ANTIPSYCHOTICS 
Aripiprazole Decrease in Clozapine level Not known 
 
ANTIBIOTICS   
Ciprofloxacin Increase in Clozapine level 1A2; 3A4 
Erythromycin  Increase in Clozapine level  3A4
 
ANTI-TUBERCULOSIS MEDICATIONS   
 Isoniazid   Increase in Clozapine level  1A2
 Rifampin Decrease in Clozapine level   1A2; 3A4
   
PROTON PUMP INHIBITORS   
Omeprazole Decrease in Clozapine level   1A2; 3A4
 
ORAL CONTRACEPTIVES   
 Ethinylestradiol  Increase in Clozapine level   1A2; 2C19
   
HERBAL MEDICATIONS
St. John’s Wort Decrease in Clozapine level  3A4 
 
SMOKING   
 Smoking  Decrease in Clozapine level   1A2 
 
CAFFEINE
 Caffeine   Increase in Clozapine level  1A2

 

Source: Singh, H., Dubin, W.R. and Kaur, S. (2015) ‘Drug interactions affecting clozapine levels’, Journal of Psychiatric Intensive Care, 11(1), pp. 52–65.

 

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Dr. Harvinder Singh, M.D. (Admin)


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