Fosamac contains Fosaprepitant, a neurokinin-1 (NK1) receptor antagonist used primarily as an antiemetic to prevent nausea and vomiting caused by chemotherapy. Fosaprepitant is the prodrug of aprepitant, which works by blocking the effects of substance P, a neurotransmitter involved in vomiting reflex.

Uses

Chemotherapy-Induced Nausea and Vomiting (CINV):

• Used in combination with other antiemetics for the prevention of acute and delayed nausea and vomiting associated with highly emetogenic cancer chemotherapy.

Postoperative Nausea and Vomiting (PONV):

• Used for the prevention of postoperative nausea and vomiting in patients undergoing surgery.

Fosaprepitant is rapidly converted to aprepitant in the body, which selectively inhibits the neurokinin-1 receptor. This blockage prevents the action of substance P in the central nervous system, thereby reducing nausea and vomiting.

Onset of Action

• The onset of action of Fosaprepitant is typically within 1-3 hours after administration.

Duration of Action

• The effects last for up to 24 to 72 hours, depending on the type of chemotherapy or surgery.

Dosage

Chemotherapy-Induced Nausea and Vomiting (CINV):

• IV dose: 150 mg administered intravenously 30 minutes before the chemotherapy session on Day 1.
• May be followed by oral aprepitant for 2 additional days.

Postoperative Nausea and Vomiting (PONV):

• IV dose: 150 mg administered as a single dose 1 hour before anesthesia induction.

Common Side Effects

• Fatigue
• Constipation
• Decreased appetite
• Headache
• Liver enzyme elevations
• Hypersensitivity reactions (rare)

Precautions

• Caution in patients with liver impairment (dose adjustment required).
• Monitor for potential drug interactions, particularly with drugs metabolized by the cytochrome P450 enzyme system (e.g., warfarin, dexamethasone).

Drug Interactions

• CYP3A4 inhibitors (e.g., ketoconazole): Can increase Fosaprepitant levels.
• CYP3A4 inducers (e.g., rifampin): Can decrease Fosaprepitant levels.
• Warfarin: Fosaprepitant can alter INR (International Normalized Ratio).
• Dexamethasone: May require dose adjustment due to interaction.

Storage

• Store at room temperature (20-25°C) in a tightly closed container. Do not freeze.