Fosaprepitant

How it works

It is rapidly converted to aprepitant, which blocks substance P at central NK1 receptors, complementing the action of a 5-HT3 antagonist and a corticosteroid in the antiemetic regimen.

Prescribing in practice

• Hypersensitivity and infusion-site reactions can occur, so it must be given as directed and stopped if a serious reaction develops.
• It interacts via CYP3A4, increasing exposure to drugs metabolised by this enzyme (including the corticosteroid co-administered) and reducing the efficacy of hormonal contraceptives.
• Use it as part of a combination antiemetic regimen rather than as monotherapy, and adjust co-administered corticosteroid as advised.

Monitoring

Monitor for infusion-related and hypersensitivity reactions and review concomitant CYP3A4 substrates for altered effect.

Counselling the patient

• Use an additional non-hormonal method of contraception during treatment and for a period afterwards.
• Report any rash, flushing or breathing difficulty during the infusion.
• This is given alongside your other anti-sickness medicines.

Evidence & guidelines

NK1 antagonist efficacy in chemotherapy-induced nausea and vomiting is supported by randomised controlled trials and reflected in oncology antiemetic guidelines.