antibioticsbooks

212 PART 5 Antiviral Drugs
Spectrum
Good: CMV, HSV-1, HSV-2, VZV, EBV
Poor: HIV
Adverse Effects
Ganciclovir and valganciclovir are the same active
drug and have the same adverse reactions. They
both have dose-dependent myelosuppression that
is relatively common, particularly when used
in higher doses or in renally impaired patients
without dose adjustment. Foscarnet is nephrotoxic
and neurotoxic, and it is reserved for patients
who have failed other therapy. Nausea, vomiting,
and diarrhea can occur from any of these agents.
Foscarnet can also cause penile ulcers. Cidofovir
is an uncommonly used agent that also exhibits
nephrotoxicity.
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Important Facts
• Oral ganciclovir has been replaced by valganciclovir,
which has much better bioavailability.
• Ganciclovir must be carefully dosed by patient
weight and renal function. Monitor patients
closely for changes in renal function when they
are on therapy.
• The package insert for valganciclovir specifies
dose adjustment for renal dysfunction but not
weight. It comes in two strengths: 900 mg and
450 mg. The dose of 900 mg BID is considered to
be equivalent to 5 mg/kg q12h of IV ganciclovir,
but it may be much more than that for an underweight
patient because it is approximately 60%
bioavailable. Consider this example for a 50-kg
patient: