Androgens are converted to estrogens by the enzyme called aromatase. This process called aromatization is inhibited by a group of drugs called aromatase inhibitors (AIs). Letrozole is a nonsteroidal inhibitor that reversibly binds aromatase. Decrease in circulating estradiol level leads to release of negative feedback at hypothalamus pituitary level, thereby increasing follicle stimulating hormone (FSH) secretion resulting in stimulation of growth of ovarian follicles. Letrozole is well tolerated and is used in different protocols of ovarian stimulation. The extended spectrum of uses includes addition with gonadotrophins in poor responders, ovarian hyperstimulation syndrome (OHSS) prevention, fertility preservation in cancer patients. Due to its wide range of use, easy availability, affordability and good tolerability, Letrozole has emerged as a first line drug for ovulation induction.
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