Foscarnet Dosing for CMV Colitis

Primary Indication for Foscarnet

The Centers for Disease Control and Prevention recommends foscarnet as an alternative agent for CMV colitis in specific clinical scenarios, including ganciclovir resistance, ganciclovir intolerance, and first-line therapy failure 1, 2, 3, 4
Foscarnet is used for ganciclovir-resistant or ganciclovir-intolerant cases, with a recommended dose of 60 mg/kg intravenously every 8 hours (or alternatively 90 mg/kg every 12 hours) for 14-21 days 1, 2, 3, 4

The Centers for Disease Control and Prevention recommends two equivalent dosing schedules: 60 mg/kg IV every 8 hours (three times daily) for 14-21 days, or 90 mg/kg IV every 12 hours (twice daily) for 14-21 days 1, 2, 6, 7
Maintenance dosing considerations include 90-120 mg/kg IV once daily for long-term suppression in HIV-infected patients with concurrent CMV retinitis 1, 2

Critical administration parameters to prevent toxicity include infusion over 1-2 hours, no faster than 1 mg/kg/minute, and concurrent saline fluid loading (1 liter normal saline with each infusion) 1, 2
The Centers for Disease Control and Prevention recommends monitoring serum creatinine at baseline, then at least twice weekly during therapy, and checking electrolytes (calcium, magnesium, potassium, phosphorus) at least twice weekly during therapy 1, 2

Doses must be modified in patients with renal insufficiency, with baseline creatinine clearance guiding initial dosing and frequent monitoring during therapy 1, 2

Renal dysfunction occurs in 7-30% of patients, and monitoring serum creatinine at baseline, then at least twice weekly during therapy is necessary to detect toxicity early 1, 2
Electrolyte disturbances, including hypocalcemia, hypomagnesemia, hypokalemia, hypophosphatemia, or hyperphosphatemia, can occur in approximately one-third of patients 1, 2

In HIV-infected patients with CMV colitis, consider discontinuing or reducing immunosuppressive therapy if feasible, and maintenance therapy may be necessary to prevent relapse 1, 2, 4
For solid organ or hematopoietic stem cell transplant recipients, reduction of immunosuppression should be attempted when treating CMV colitis, and high-dose valganciclovir may be an alternative if foscarnet causes acute kidney injury 8
In IBD patients with CMV colitis superinfection, foscarnet is used for ganciclovir-resistant or ganciclovir-intolerant cases, and temporary discontinuation of immunomodulators is associated with improved outcomes and decreased mortality 3, 4