Cyclophosphamide

How it works

It is a prodrug metabolised in the liver to active alkylating species (including phosphoramide mustard) that cross-link DNA strands, impairing replication and inducing apoptosis in rapidly dividing and immune cells.

Prescribing in practice

• It is toxic to the bladder urothelium (haemorrhagic cystitis) and carries a long-term risk of bladder cancer, so adequate hydration and, with higher exposures, mesna uroprotection are used.
• Causes bone marrow suppression, increased infection risk, infertility and is teratogenic.
• A cumulative-dose-limited cytotoxic that must be prescribed under specialist supervision in line with the SPC and disease-specific protocols.

Monitoring

Monitor full blood count, renal and hepatic function and urinalysis for haematuria, with maintained hydration around administration.

Counselling the patient

• Maintain a good fluid intake and empty the bladder regularly; report any blood in the urine.
• Report fever or other signs of infection without delay.
• Discuss fertility preservation before treatment and use effective contraception, as the drug can harm a pregnancy.

Evidence & guidelines

Its use in severe vasculitis and lupus is supported by long-standing trial evidence and current rheumatology guidance, alongside the SPC.