Aromatase Inhibitors: New Drug of Choice for Induction of Ovulation

Anovulation accounts for around 20% cases of infertilityeven when other fertility factors are normal. ClomipheneCitrate (CC), the oral anti-estrogen has long been used asthe first line drug for induction of ovulation. Clomipheneis associated with a high ovulation (60-80%) but relativelypoor pregnancy rate (30-40%). CC leads to long lastingestrogen receptor depletion. Because of its long half-life(2 weeks), CC possibly exerts a negative feedback effect onthe cervical mucous and endometrial development withsubsequent implantation failure. The aromatase inhibitorletrozole (originally approved for use in postmenopausalwomen with breast cancer to suppress estrogen production) is now increasingly being used by fertility specialists worldwide for ovulation induction.With a halflife of around 45 hours, letrozole possibly avoids the adverse effects of CC on endometrium. Preliminary trials have shown impressive prospects of aromatase inhibitor letrozole for induction of ovulation (even in CC resistant cases) with satisfactory pregnancy rates. Letrozole is now being marketed by our local pharmaceutical companies. Though large scale randomized controlled trials are not yet available, letrozole holds a very promising chance of replacing CC in near future.