antibioticsbooks

208 PART 5 Antiviral Drugs
Adverse Effects
These drugs are generally well tolerated with
few adverse effects. The most concerning adverse
effect is nephrotoxicity through either crystallization
or acute interstitial nephritis (AIN), most
commonly associated with IV acyclovir in higher
doses. Crystallization is preventable through
hydration and correct dosing in renally impaired
patients. Seizures, tremors, or other CNS effects
can also occur. Nausea, diarrhea, and rash are
more common. Thrombotic thrombocytopenic purpura
has been reported with valacyclovir in HIV
patients.
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Important Facts
• Valacyclovir is a pro-drug of acyclovir with substantially
improved bioavailability and lessfrequent
dosing. Its disadvantage is higher
cost. Famciclovir is a pro-drug of penciclovir,
an agent that is available only as a topical
preparation.
• Acyclovir dosing varies widely by indication
and host status. Be sure to double-check that it
is appropriate for your patients.
• Acyclovir is most nephrotoxic in combination
with diuretics or other nephrotoxins.
Keep your patients hydrated during acyclovir
therapy, particularly if it is given in higher IV
doses.
What They’re Good For
Acyclovir is the drug of choice for severe or difficultto-treat
HSV infections, such as encephalitis or
severe HSV outbreaks among HIV patients. Any of