Foscarnet sodium

How it works

It reversibly blocks the pyrophosphate binding site of viral DNA polymerase and reverse transcriptase, inhibiting viral nucleic acid synthesis without requiring intracellular activation by viral kinases.

Prescribing in practice

• Nephrotoxicity is the principal dose-limiting toxicity; maintain adequate hydration, monitor renal function closely and adjust the regimen for renal impairment.
• Causes electrolyte disturbances including hypocalcaemia, hypomagnesaemia, hypokalaemia and hyperphosphataemia or hypophosphataemia, which can precipitate arrhythmias and seizures.
• Administer by controlled infusion through a suitable line and consult the SPC and current prescribing references for reconstitution and infusion-rate requirements.

Monitoring

Monitor renal function and serum electrolytes (including calcium, magnesium, potassium and phosphate) regularly throughout treatment, with more frequent checks during induction.

Counselling the patient

• Report numbness, tingling around the mouth, muscle twitching or seizures, as these may indicate electrolyte disturbance.
• Maintaining good fluid intake helps protect the kidneys during treatment.
• Attend all scheduled blood tests and ophthalmology reviews as advised.

Evidence & guidelines

Foscarnet is an established option for CMV disease and aciclovir-resistant herpesvirus infection in immunocompromised patients, as reflected in UK and international guidance.