Megace (Megestrol Acetate)

Megestrol acetate is used in the management of conditions associated with severe weight loss and hormone‑responsive cancers, where it acts as an appetite stimulant and a hormonal antineoplastic agent.

• Cachexia associated with AIDS or cancer: stimulates appetite, increases caloric intake and helps patients gain weight.
• Advanced breast cancer: exerts antineoplastic effects through progesterone receptor binding, contributing to disease control in hormone‑sensitive tumors.
• Endometrial cancer: acts as a hormonal therapy that can slow tumor growth and provide palliation in selected patients.

• Megestrol acetate binds to intracellular progesterone receptors, mimicking the action of natural progesterone. This receptor activation leads to transcriptional changes that produce glucocorticoid‑like effects, enhancing appetite and promoting protein synthesis. In hormone‑sensitive tumors, the drug exerts antineoplastic activity by modulating cell proliferation and inducing apoptosis through progesterone‑mediated pathways. The combined effect also reduces inflammatory cytokine production, contributing to improved nutritional status.

Megestrol acetate may cause a range of adverse reactions, which are categorized by frequency.

Common Side Effects

• Nausea: mild to moderate stomach upset that may affect appetite.
• Edema: fluid retention causing swelling of the ankles, feet, or hands.
• Weight gain: increase in body weight beyond intended therapeutic effect.
• Hot flashes: transient sensation of warmth accompanied by sweating.
• Fatigue: persistent tiredness or lack of energy during daily activities.

Serious or Rare Side Effects

• Thromboembolic events: formation of blood clots such as deep‑vein thrombosis or pulmonary embolism, which can be life‑threatening.
• Adrenal suppression: decreased endogenous cortisol production leading to potential adrenal insufficiency.
• Hyperglycemia: significant rise in blood glucose levels, particularly concerning for patients with diabetes.
• Liver function abnormalities: elevated liver enzymes indicating possible hepatic injury.

When prescribing megestrol acetate, clinicians should consider several safety precautions to minimize risks.

• Assess baseline weight and nutritional status: evaluate before initiating therapy.
• Monitor blood glucose: check fasting glucose or HbA1c periodically.
• Evaluate for thromboembolic risk: screen for history of clotting disorders.
• Review liver function tests: perform baseline and periodic LFTs.
• Consider drug interactions: avoid concurrent use with strong CYP3A4 inducers without adjustment.
• Store at ambient temperature: keep tablets below 25 °C in the original container, protected from moisture.

Megestrol acetate can interact with other medicines, affecting its efficacy or safety.

Major Interactions (Avoid)

• CYP3A4 inducers (e.g., rifampin, phenytoin): may reduce plasma concentrations of megestrol acetate.
• Anticoagulants (e.g., warfarin): increased risk of thrombosis due to additive pro‑coagulant effect.

Moderate Interactions (Monitor Closely)

• Antidiabetic agents (e.g., insulin, sulfonylureas): may require dose adjustment because megestrol acetate can raise blood glucose.
• Corticosteroids: combined glucocorticoid‑like activity may enhance fluid retention and hyperglycemia.
• Hormonal therapies (e.g., tamoxifen): potential additive hormonal effects necessitate clinical monitoring.