Inhibition of human placental aromatase by mefloquine.

Aromatase activity of human placental microsomes was inhibited competitively by the antimalarial drug, mefloquine, but not by the related drug, chloroquine. In the absence of any drug, the Km for testosterone was 47.1 +/- 2.3 nmol/l (mean +/- SD, n = 2). In the presence of chloroquine 500 mumol/l, the Km remained unchanged (47.4 +/- 1.8 nmol/l (mean +/- SD, n = 2), whereas mefloquine inhibited competitively with respect to substrate with a Ki value of 72 +/- 4.2 mumol/l (mean +/- SD, n = 2).