Valaciclovir
Valaciclovir is a prodrug of aciclovir: the body converts it after absorption, so more of the active antiviral reaches the blood from each dose. The active form blocks the viral DNA polymerase of herpes viruses and stops them replicating. It is used for viral infections including cold sores, genital herpes and shingles.
It can be taken with or without food. Because it delivers a larger amount of aciclovir, keeping fluid intake up matters, since the drug is cleared by the kidneys and can crystallise there if a person is dehydrated. Reduced kidney function calls for caution and dose adjustment decided by a doctor, and creatinine and eGFR are the markers followed during longer or repeated courses. It is most effective when begun at the earliest symptoms.
A sharp fall in urine output, swelling, or new confusion, drowsiness or hallucinations are reasons to see a doctor promptly, especially where kidney function is already impaired. Unusual bruising, bleeding or widespread rash also needs medical review.
Reference information, not medical advice. Discuss any change with your doctor.