Exemis

Exemestane is an irreversible, steroidal aromatase inactivator. Its structure is close to that of androstenedione, the natural substrate of the aromatase enzyme. Because of this, the enzyme treats exemestane as a false substrate and converts it into an intermediate. That intermediate binds irreversibly to the active site of the enzyme and inactivates it, which is also called suicide inhibition.

In postmenopausal women, exemestane lowers circulating estrogen concentrations significantly. It has no detectable effect on the adrenal biosynthesis of corticosteroids or aldosterone. It also has no effect on other enzymes in the steroidogenic pathway, at least up to a concentration 600 times higher than the one that inhibits the aromatase enzyme.

Exemestane can harm an unborn baby when it is given to a pregnant woman. This is based on animal studies and on how the medicine works. There are some human case reports, but they are too limited to say what the risk really is. In animal studies, pregnant rats and rabbits given exemestane had more abortions, toxicity to the embryo and fetus, and longer pregnancies with abnormal or difficult labour. Pregnant women should be told about the possible risk to the baby.

The background risk of major birth defects and miscarriage is not known for the population this medicine is meant for. In the general population of the US, the estimated background risk in clinically recognised pregnancies is 2-4% for major birth defects and 15-20% for miscarriage.

Nobody knows yet whether exemestane passes into human milk, or what it does to a breastfed infant or to milk production. In rats, the medicine is found in milk at levels similar to those in the mother's plasma. Because exemestane could cause serious adverse reactions in a breastfed infant, a woman should not breastfeed during treatment and for 1 month after her final dose.

Store Exemestane below 30°C, away from light and moisture. Keep it out of the reach of children.