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## Megestrol Acetate (Megace ES, Megace)
### Overview
Megestrol acetate is a synthetic derivative of progesterone. It is a progestin with antileukemic, antineoplastic, and antiestrogenic properties.
### Primary Indications
* **Cancer therapy:** Treatment of advanced breast cancer and endometrial cancer.
* **Appetite stimulation/weight gain:** Management of anorexia, cachexia, or unexplained weight loss in patients with acquired immunodeficiency syndrome (AIDS).
### Adult Dosing
* **Breast Cancer:** 160 mg (4 mL) once daily.
* **Endometrial Cancer:** 40 mg (1 mL) orally four times daily (160 mg/day total).
* **Appetite Stimulation/Weight Gain:** 400 mg (10 mL) to 800 mg (20 mL) once daily. Dosing for this indication is highly variable and depends on patient response and clinical judgment.
### Pediatric Dosing
There is no established pediatric dosing for megestrol acetate.
### Dose Adjustments
* **Renal Impairment:** No specific dose adjustments are recommended, but caution is advised.
* **Hepatic Impairment:** No specific dose adjustments are recommended, but caution is advised.
### Contraindications
* Known hypersensitivity to megestrol acetate or any component of the formulation.
* Pregnancy.
### Adverse Effects
* **Common:** Weight gain, increased appetite, hot flashes, hypertension, dyspnea, nausea, diarrhea, rash, vaginal bleeding or discharge, impotence, amenorrhea.
* **Serious:** Thrombotic events (deep vein thrombosis, pulmonary embolism), adrenal insufficiency (especially with abrupt discontinuation after prolonged use), hyperglycemia, new-onset diabetes, exacerbation of pre-existing diabetes, cardiac events (myocardial infarction, stroke).
### Key Drug Interactions
* **Aminoglutethimide:** May decrease the plasma concentrations of megestrol acetate.
* **CYP3A4 Inhibitors/Inducers:** May alter megestrol acetate concentrations, though clinical significance is not fully established.
* **Dofetilide:** Concomitant use is contraindicated due to the risk of increased dofetilide plasma concentrations and potential for serious ventricular arrhythmias.
### Monitoring
* **Cancer Therapy:** Tumor response, signs of thrombosis, vital signs.
* **Appetite/Weight Gain:** Body weight, appetite, signs of fluid retention, adrenal function if abruptly discontinued after long-term use (typically > 3 months).
* **General:** Blood glucose, blood pressure, electrolytes.
### Clinical Pearls
* Abrupt discontinuation after prolonged therapy (especially for appetite stimulation) can lead to adrenal insufficiency. Tapering may be necessary.
* Weight gain is a common and often desired effect for appetite stimulation, but it can be significant.
* Thromboembolic events are a serious risk, particularly in patients with a history of these events.
* Use with caution in patients with diabetes or a history of hyperglycemia.
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*Disclaimer: This information is intended for healthcare professionals and is not a substitute for professional medical advice. Always consult the most current prescribing information and relevant guidelines for definitive patient care decisions. Drug information can change, and local protocols may dictate specific dosing strategies.*
