Drug-drug interaction studies with mirtazapine and carbamazepine in healthy male subjects.

In two studies, the effects of the potentially interacting drugs mirtazapine and carbamazepine on their pharmacokinetics have been investigated. Subjects were treated with carbamazepine combined with placebo for 21 days and subsequently with carbamazepine combined with mirtazapine for another 7 days (Study A) or with mirtazapine combined with placebo for 7 days and subsequently mirtazapine combined with carbamazepine for another 21 days (Study B). Pharmacokinetic results indicate that carbamazepine decreased significantly AUC and Cmax values for mirtazapine and increased values for demethyl-mirtazapine Cmax. Mirtazapine had no effect on carbamazepine pharmacokinetic parameters, but did lower carbamazepine-10,11-epoxide levels. Mirtazapine did not affect the single dose kinetics or the enzyme inducing properties of carbamazepine. VAMRS alertness scores reflected the somnolence-inducing effects of carbamazepine and mirtazapine and psychometric test results revealed impairment of specific tasks. The combination was safe and routine laboratory testing did not reveal clinically relevant abnormalities. The dose of mirtazapine in patients on carbamazepine may have to be increased for optimal antidepressant efficacy.