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# Megestrol Acetate (Megace)
## Overview
Megestrol acetate is a synthetic progestin with antineoplastic and antiestrogenic properties. It is primarily used in oncology and for appetite stimulation in specific patient populations.
## Primary Indications
* Treatment of advanced breast cancer (hormone receptor-positive, metastatic) in postmenopausal women.
* Treatment of advanced endometrial cancer (hormone receptor-positive, metastatic) in postmenopausal women.
* Management of anorexia, cachexia, or unexplained significant weight loss in patients with acquired immunodeficiency syndrome (AIDS).
## Adult Dosing
* **Breast Cancer:** 160 mg orally once daily. Higher doses (e.g., 400-800 mg/day) have been used, but efficacy at these doses is not definitively established over 160 mg/day.
* **Endometrial Cancer:** 40 mg orally four times daily (160 mg/day total).
* **Appetite Stimulation/Cachexia in AIDS:** 400-800 mg orally once daily. Doses as low as 100-200 mg/day have shown efficacy for weight gain, but higher doses are often required to achieve and maintain weight.
## Pediatric Dosing
There is no established pediatric dosing for megestrol acetate. Its use in children is generally not recommended due to lack of safety and efficacy data.
## Dose Adjustments
* **Renal Impairment:** No specific dose adjustment is recommended, as megestrol acetate is not significantly removed by dialysis. However, caution and close monitoring are advised.
* **Hepatic Impairment:** No specific dose adjustment is recommended.
## Contraindications
* Known or suspected pregnancy.
* Known hypersensitivity to megestrol acetate or any component of the formulation.
## Adverse Effects
* **Common:** Weight gain, increased appetite, hot flashes, nausea, vomiting, diarrhea, abdominal pain, edema, hypertension, dyspnea.
* **Less Common/Serious:** Thrombophlebitis and thromboembolic phenomena (pulmonary embolism, deep vein thrombosis), adrenal insufficiency (especially with abrupt discontinuation after prolonged use), hyperglycemia, new-onset diabetes, exacerbation of existing diabetes, vaginal bleeding, amenorrhea, rash, hair loss.
* **Malignancy Risk:** Increased risk of endometrial cancer if used for prolonged periods in women with a uterus who have not undergone hysterectomy (though primarily used for other indications).
## Key Drug Interactions
* **CYP3A4 Inhibitors/Inducers:** May alter megestrol acetate plasma concentrations. Caution and potential dose adjustment may be needed.
* **Diabetes Medications:** Megestrol acetate can cause hyperglycemia and affect glycemic control. Close monitoring of blood glucose and potential adjustment of antidiabetic medications is necessary.
## Monitoring
* **Weight and Appetite:** Regular assessment of weight changes and appetite is crucial, especially in patients with cachexia.
* **Electrolytes:** Monitor electrolytes (sodium, potassium) due to potential for edema and adrenal insufficiency.
* **Blood Glucose:** Monitor blood glucose levels, particularly in patients with diabetes or at risk for developing diabetes.
* **Signs of Thromboembolism:** Vigilantly monitor for symptoms of DVT or pulmonary embolism (leg pain/swelling, chest pain, shortness of breath).
* **Adrenal Function:** Consider monitoring adrenal function tests if prolonged use or signs/symptoms of adrenal insufficiency occur, especially prior to discontinuation.
## Clinical Pearls
* Megestrol acetate is often a salvage therapy for advanced hormone-sensitive cancers.
* The weight gain associated with megestrol acetate is often due to fluid retention and increased fat mass, not necessarily lean body mass.
* Abrupt discontinuation after prolonged, high-dose therapy can lead to adrenal insufficiency. Tapering may be considered in select cases, though definitive guidance is lacking.
* Oral suspension formulations may contain sugar; consider in diabetic patients.
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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 literature before making any clinical decisions. Local protocols and patient-specific factors may influence treatment.
