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## Megestrol Acetate
### Overview
Megestrol acetate is a synthetic derivative of progesterone. It is an anti-androgenic and anti-progestational agent.
### Primary Indications
* Management of advanced breast cancer (palliative).
* Management of advanced endometrial cancer (palliative).
* Treatment of anorexia, cachexia, or unexplained significant weight loss in patients with acquired immunodeficiency syndrome (AIDS).
### Adult Dosing
* **Advanced Breast Cancer:** 160 mg orally once daily.
* **Advanced Endometrial Cancer:** 40 mg orally four times daily (total 160 mg/day).
* **Anorexia/Cachexia/Weight Loss in AIDS:** 400-800 mg orally once daily.
### Pediatric Dosing
Safety and efficacy in pediatric patients have not been established.
### Dose Adjustments
* **Renal Impairment:** No specific dose adjustments are recommended.
* **Hepatic Impairment:** No specific dose adjustments are recommended.
### Contraindications
* Known hypersensitivity to megestrol acetate or any component of the formulation.
* Pregnancy.
* Use in patients with a history of thrombophlebitis or thromboembolic events.
### Adverse Effects
* **Common:** Weight gain, increased appetite, edema, hot flashes, dyspnea, nausea, vomiting, diarrhea, abdominal pain, rash, alopecia, fatigue, hypertension, urinary incontinence.
* **Serious:** Thromboembolic events (deep vein thrombosis, pulmonary embolism, stroke, myocardial infarction), adrenal insufficiency (especially with abrupt withdrawal after prolonged use), hyperglycemia, new onset diabetes, exacerbation of existing diabetes.
### Key Drug Interactions
* **CYP3A4 Inhibitors (e.g., ketoconazole, ritonavir):** May increase megestrol acetate concentrations. Monitor for increased adverse effects.
* **CYP3A4 Inducers (e.g., rifampin, phenytoin, St. John's wort):** May decrease megestrol acetate concentrations. Monitor for decreased efficacy.
* **Anticoagulants (e.g., warfarin):** May alter anticoagulant effect. Monitor INR closely.
### Monitoring
* **Weight and appetite:** Regularly assess for desired effects and potential fluid retention.
* **Thromboembolic events:** Educate patients on signs/symptoms and monitor for any suspicion.
* **Adrenal function:** Monitor for signs of adrenal insufficiency, especially with prolonged use or abrupt discontinuation.
* **Blood glucose:** Monitor in patients with diabetes or those at risk for developing diabetes.
* **Electrolytes:** Monitor as clinically indicated.
### Clinical Pearls
* Megestrol acetate is associated with significant weight gain, which can be due to increased appetite or fluid retention. Distinguish between these if possible.
* Abrupt discontinuation after prolonged therapy can lead to adrenal insufficiency. Taper dose if clinically appropriate.
* Due to the risk of thromboembolic events, use with caution in patients with a history of such events.
* Ensure patients are counseled on the risks and benefits, especially regarding potential thromboembolic and metabolic complications.
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**Disclaimer:** This information is intended for clinical use only. It is essential to consult the most current prescribing information and relevant clinical guidelines before administering any medication. Dosing and recommendations may vary based on individual patient factors and local protocols.
