Evaluate allergies, renal function, hydration status, and history of thrombotic microangiopathy before prescribing valacyclovir.
Absolute contraindications include prior hypersensitivity to valacyclovir or acyclovir. Dose reduction is mandatory in renal impairment (CrCl <50 mL/min/1.73 m²), and the drug should be avoided in dehydrated patients until fluid status is corrected. Rare cases of thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS) have occurred in immunocompromised hosts receiving high doses.
Serious cutaneous or anaphylactic reactions require permanent avoidance and use of a nonrelated antiviral.
Rechallenge after TTP/HUS is discouraged due to risk of irreversible renal failure and death.
Dose reductions are required to prevent crystal nephropathy; ensure aggressive hydration and monitor renal function.
Additive renal injury risk warrants close monitoring and consideration of alternative antivirals.
Data support use when benefits outweigh risks, but obstetric or lactation consultation is recommended for prolonged courses.