An anti-sickness injection for chemotherapy
Fosaprepitant
An injection given with chemotherapy to help prevent sickness, especially the delayed kind.
What is Fosaprepitant?
Fosaprepitant is an anti-sickness medicine given as an injection or drip into a vein, usually before chemotherapy, to help prevent the nausea and vomiting it can cause. It belongs to a group called NK1 receptor blockers and is especially useful for the delayed sickness that comes a day or more after treatment. It is given together with other anti-sickness medicines — typically a steroid and a 5HT3 blocker — for the best effect. It can interact with several other medicines, so your team will check what else you take.
Education and reference only. This is a plain-language guide to Fosaprepitant — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Fosaprepitant is an anti-sickness (antiemetic) medicine of the NK1 receptor antagonist group. It is given as an injection or infusion into a vein, usually on the day of chemotherapy, to help prevent the nausea and vomiting that chemotherapy can cause. In the body it is rapidly converted into aprepitant, the active medicine. It is particularly aimed at preventing delayed sickness, which can occur over the days after treatment, and is used alongside other anti-sickness medicines.
How it works
Chemotherapy can trigger sickness partly through a brain chemical called substance P acting on NK1 receptors. Fosaprepitant is turned in the body into aprepitant, which blocks these NK1 receptors and so dampens this trigger, helping to prevent both immediate and, importantly, delayed nausea and vomiting. Because different chemotherapy triggers work through different pathways, it is given together with a steroid and a 5HT3 blocker, which act on other pathways, for fuller protection. Being given into a vein, it acts quickly without needing tablets.
Company & origin
Originated / developed by: Generic (originator Merck/MSD).
An NK1 receptor blocker given by injection in the UK to help prevent sickness from chemotherapy.
Practical use
How to take Fosaprepitant
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- It is given by a healthcare professional as an injection or drip into a vein, usually before chemotherapy.
- It is used together with your other anti-sickness medicines, such as a steroid and a 5HT3 blocker.
- Tell your team about all your medicines, including warfarin and hormonal contraception, as it interacts with several.
- Use extra or alternative contraception during and for a while after treatment if advised, as it can make hormonal contraception less reliable.
- Report any reaction during or after the infusion, such as flushing, rash or breathing problems.
Weighing it up
Advantages & disadvantages of Fosaprepitant
Advantages
- Helps prevent chemotherapy sickness, especially the delayed kind that comes a day or more later.
- Given into a vein, so it is useful when swallowing tablets is difficult.
- Works through a different pathway from steroids and 5HT3 blockers, adding to their effect.
Disadvantages
- Must be given by injection or drip by a healthcare professional.
- Interacts with several medicines, including some steroids, warfarin and hormonal contraception.
- Can occasionally cause drip-site reactions or, rarely, an allergic reaction during the infusion.
Practical use
Good to know
Fosaprepitant is used as part of a combination, not on its own — typically with a steroid (such as dexamethasone) and a 5HT3 blocker (such as ondansetron) — because together they cover the different ways chemotherapy causes sickness. Its particular strength is preventing the delayed sickness that can appear a day or more after treatment. As an injection or drip, it is convenient when swallowing tablets is difficult, though it can occasionally cause reactions at the drip site or, rarely, an allergic reaction during the infusion. An important practical point is that it interacts with several medicines, including some steroids, certain chemotherapy drugs, warfarin and hormonal contraception, so tell your team everything you take and use extra contraceptive precautions as advised.
Who should not take it / use with caution
- People who have had a serious allergic reaction to fosaprepitant or aprepitant should not be given it.
- Used with caution and adjustment where it interacts strongly with other essential medicines.
- Care is needed in significant liver problems, where specialist advice is required.
Monitoring
- Checking how well the combination controls nausea and vomiting after chemotherapy.
- Watching for reactions during the infusion.
- Reviewing interacting medicines, such as warfarin (INR) and contraception, around treatment.
Side effects
- Tiredness, hiccups, headache, constipation or diarrhoea, and a reduced appetite are among the more common effects.
- Reactions at the drip site, such as redness or discomfort.
- Rarely, an allergic reaction during the infusion with flushing, rash, low blood pressure or breathing problems.
Key interactions
- It affects how the body handles some medicines, including the steroid dexamethasone, which may need a lower dose.
- It can make hormonal contraception less reliable, so extra or alternative contraception is advised.
- It can affect warfarin control and interacts with certain chemotherapy and other medicines, so the full list must be checked.
Available as: Powder made up into a solution for injection or infusion into a vein.
Answers
Fosaprepitant: frequently asked questions
How is fosaprepitant given?
It is given by a healthcare professional as an injection or drip into a vein, usually before your chemotherapy.
Why is it given with other anti-sickness medicines?
Chemotherapy causes sickness in more than one way, so it is combined with a steroid and a 5HT3 blocker to cover the different pathways for better protection.
What is it especially good for?
It is particularly useful for preventing delayed sickness, the nausea and vomiting that can come a day or more after chemotherapy.
Does it affect my other medicines?
Yes, it interacts with several medicines, including some steroids, warfarin and hormonal contraception, so tell your team everything you take.
Could it affect my contraception?
It can make hormonal contraception less reliable, so use extra or alternative contraception during and for a while after treatment if advised.
The wider class
About NK1 receptor antagonist antiemetic
Fosaprepitant belongs to the nk1 receptor antagonist antiemetic class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF
- NICE CKS
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