What is Megestrol acetate - Meaning and definition

Published by Roberto Wenk. Reviewed by Alison Ramsey. Last updated date: January 9, 2019.

The acetate salt of megestrol, a synthetic derivative of the naturally occurring female sex hormone progesterone, with progestogenic, antiestrogenic, and antineoplastic activities.
Mimicking the action of progesterone, megestrol binds to and activates nuclear progesterone receptors (PRs) in the reproductive system and pituitary; ligand-receptor complexes are translocated to the nucleus where they bind to progesterone response elements (PREs) located on target genes.
Megestrol´s antineoplastic activity against estrogen-responsive tumors may be due, in part, to the suppression of pituitary gonadotrophin production and the resultant decrease in ovarian estrogen secretion; interference with the estrogen receptor complex in its interaction with genes; and, as part of the progesterone receptor complex, direct interaction with the genome and downregulation of specific estrogen-responsive genes. This agent may also directly kill tumor cells.

National Cancer Institute. NCI Drug Dictionary. Internet. September 15, 2009.

Published by Roberto Wenk. Reviewed by Alison Ramsey. Last updated date: January 9, 2019.

Megestrol acetate has been extensively studied as an appetite stimulant.

Clinical trials have demonstrated that megestrol is:
- equally efficacious to dexamethasone as an appetite stimulant;
- superior to dronabinol in appetite stimulation and non-fluid weight gain;
- effective, when used concurrently with radiation therapy in lung or head and neck cancer, to reduce treatment associated weight loss; and
- associated with fewer side effects than corticosteroids.

However, despite these apparent benefits, available data suggests that weight gain is largely adipose tissue (not lean muscle) and only one study has demonstrated a quality-of-life benefit; no study has shown a survival advantage.
Overall only 20-30% of advanced cancer patients will have a significant response (weight gain > 5%), with a median response duration of 6-8 weeks.

The optimal timing to initiate treatment with megestrol (prophylactic or therapeutic) and the optimal duration of therapy are unknown.

Megestrol is dosed orally, once daily. There is an increasing dose/response curve from 160 to 800 mg/day; doses above 800 mg/day have no additional benefit. Different strategies include beginning at 400 mg per day and titrating for effect to 800 mg/day. Alternatively, dosing can begin at 800 mg/day.

Side effects can include thromboembolic events (use with caution in patients with a history of thromboembolism), adrenal suppression with insufficiency upon abrupt discontinuation, hypertension, hyperglycemia.

See reference for details.

Adapted from Salacz M. Palliative Care Network of Wisconsin. Fast facts and concepts #100. Megestrol acetate for cancer anorexia/cachexia. Internet. Accessed on January 25, 2016.

Megestrol acetate

To cite