[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [NK1 receptor antagonists](https://durgical.com/en/pharmacology/classes/nk1-receptor-antagonists/) › Fosaprepitant [Pharmacology](https://durgical.com/en/pharmacology/) · [NK1 receptor antagonists](https://durgical.com/en/pharmacology/classes/nk1-receptor-antagonists/) # Fosaprepitant The intravenous prodrug of aprepitant, given before chemotherapy to prevent vomiting. It can irritate the vein and is not mixed with calcium solutions. Updated 2026-11-01 - Class: [NK1 receptor antagonists](https://durgical.com/en/pharmacology/classes/nk1-receptor-antagonists/) - Receptor: Tachykinin receptor 1 (NK1, substance P receptor) - ATC code: A04AD12 ◎**Tachykinin receptor 1 (NK1, substance P receptor)**Fosaprepitant ⓘ The figure shows aprepitant, the active drug that fosaprepitant becomes in the body, bound to the human NK1 receptor. **Target in 3D:** Tachykinin receptor 1 (NK1, substance P receptor). PDB structure 6HLO (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/6HLO) · Drag to rotate · pinch to zoom ## Mechanism of action Fosaprepitant is a water-soluble phosphate prodrug. After intravenous infusion, phosphatases in the liver and many other tissues rapidly remove the phosphate and release aprepitant, which blocks substance P at brain NK1 receptors and prevents acute and delayed chemotherapy-induced vomiting. - Fosaprepitant is infused intravenously - Tissue phosphatases rapidly convert it to aprepitant - Aprepitant occupies brain NK1 receptors and blocks substance P - Acute and delayed chemotherapy vomiting are prevented ## Pharmacokinetics **Absorption** Given intravenously; it is converted to aprepitant within about half an hour of the end of the infusion. **Metabolism** Converted to aprepitant in the liver, kidney, lung and gut; aprepitant is then metabolised mainly by CYP3A4. **Half-life** Aprepitant formed from it has a half-life of about 9–13 hours. ## Indications - Prevention of acute and delayed nausea and vomiting from highly emetogenic chemotherapy, and of delayed nausea and vomiting from moderately emetogenic chemotherapy, with a 5-HT3 antagonist and dexamethasone. ## Adverse effects ### Common - Fatigue, weakness and diarrhoea - Low neutrophil counts in trials (given with chemotherapy) - Infusion-site pain, redness or swelling ### Serious (rare, important) - Hypersensitivity reactions, including anaphylaxis and anaphylactic shock, during or soon after the infusion - Infusion-site thrombophlebitis, necrosis and vasculitis, mostly with vesicant chemotherapy - Lower INR in patients on warfarin ## Contraindications - Hypersensitivity to fosaprepitant, aprepitant or any component - Use with pimozide ## Key interactions **Dexamethasone** Higher dexamethasone levels (CYP3A4 inhibition by aprepitant); its dose is adjusted. **Warfarin** Lower INR; it is checked in the weeks after the dose. **Hormonal contraceptives** Lower efficacy during and after treatment; a back-up method is used. **Solutions with calcium or magnesium (Ringer's lactate, Hartmann's)** Physically incompatible; it is not mixed or run with them. ## What is monitored - Vital signs and signs of anaphylaxis during and after the infusion - The infusion site, especially when vesicant chemotherapy is also given - INR in patients on warfarin ## Administration and safety - Reconstituted and diluted only in compatible fluids; never with solutions containing calcium or magnesium such as Ringer's lactate - Infused into a good vein, avoiding small veins; the infusion is stopped if the site reacts - Given before chemotherapy as part of a regimen with a setron and dexamethasone - If a hypersensitivity reaction occurs it is stopped and not given again ## Nursing care - Check the line and the diluent: no Ringer's lactate or other calcium-containing fluids - Watch for flushing, rash, breathlessness or low blood pressure during the infusion - Inspect the site for pain, redness or swelling during and after - Teach women using hormonal contraception to use a back-up method ## Pregnancy and breastfeeding Data in pregnant women are not enough to define a risk; animal studies showed no developmental harm. ## Memory aid «FOS-aprepitant = PHOSPHATE ticket»: the phosphate lets it travel in the drip, the body cuts it off, and aprepitant does the work; keep it away from calcium in the line. ## Test yourself Think of the answer, then tap the question to see it. ## What is fosaprepitant, and what does it become in the body? A water-soluble phosphate prodrug for intravenous use, rapidly converted to aprepitant. ## Which IV fluids are incompatible with fosaprepitant? Solutions with divalent cations such as calcium or magnesium, including Ringer's lactate and Hartmann's solution. ## Which local reaction is a known risk of fosaprepitant infusion? Infusion-site reactions such as thrombophlebitis, necrosis and vasculitis, mostly with vesicant chemotherapy. [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/fosaprepitant/) ## Related drugs - [Aprepitant](https://durgical.com/en/pharmacology/aprepitant/) - [Ondansetron](https://durgical.com/en/pharmacology/ondansetron/) - [Dexamethasone](https://durgical.com/en/pharmacology/dexamethasone/) [← Back to the class: NK1 receptor antagonists](https://durgical.com/en/pharmacology/classes/nk1-receptor-antagonists/) Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given. Sources: [DailyMed - FOSAPREPITANT DIMEGLUMINE injection, powder, lyophilized, for solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=19919480-960b-4741-9611-c133d68512f5) (DailyMed (U.S. National Library of Medicine), 2026); [DailyMed - APREPITANT capsule APREPITANT kit](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=d72e0e10-4557-41b0-b65d-d395468cad19) (DailyMed (U.S. National Library of Medicine), 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=A04AD12&showdescription=yes) (WHO Collaborating Centre for Drug Statistics Methodology, 2026). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/pharmacology/fosaprepitant/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/fosaprepitant/