Possible levomepromazine-clozapine interaction: two case reports

Objective: To report and comment upon two cases of suspected pharmacological interaction between the “classical” neuroleptic levomepromazine (LMP) and the “atypical” antipsychotic clozapine (CLZ). Case summary: The patients who simultaneously took the two drugs had unusually low plasma levels of CLZ and its metabolites, even though they took high doses of CLZ. The patients were considered “non-responders” to the treatment by the psychiatrist. When LMP was withdrawn from the therapy, plasma concentrations of CLZ returned to therapeutic levels and one of the two patients experienced the anticipated therapeutic response. Discussion: No information can be found in the literature regarding possible interactions between LMP and CLZ. However, the results of the two cases reported herein point out to a possible lack of therapeutic efficacy of CLZ therapy during this kind of polypharmacy. Conclusion: While two cases are too few to draw any conclusion, it would be prudent on the part of psychiatrists to consider a possible drug interaction in patients receiving both CLZ and LMP who fail to respond to the therapy.