Pharmacology · 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
The figure shows aprepitant, the active drug that fosaprepitant becomes in the body, bound to the human NK1 receptor.
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
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.
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.
Related drugs
← Back to the class: 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 (DailyMed (U.S. National Library of Medicine), 2026); DailyMed - APREPITANT capsule APREPITANT kit (DailyMed (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (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.