Valtrex 500 mg (Valaciclovir): Uses, Safety and Interactions

What Valtrex treats

Valtrex 500 mg film-coated tablets contain valaciclovir, also spelled valacyclovir. It is converted in the body to aciclovir. This summary concerns the UK oral product information, not an eye preparation or an assumption that every national licence is identical. Listed uses include shingles in adults and treatment or suppression of certain herpes simplex infections, including genital herpes and cold sores in eligible age groups. Specialist cytomegalovirus prevention after organ transplantation is another licensed use.

Treatment is indication-specific

The same tablet strength may be used in very different treatment plans. Kidney function, immune status and the infection being treated affect the prescription. Valtrex should not be selected solely because a skin lesion resembles a previous episode. Suppressive therapy does not remove the need for measures to reduce genital-herpes transmission. Questions about eye symptoms, extensive disease or illness in an immunocompromised person require medical assessment, rather than a self-selected course.

Side effects and urgent warning signs

Headache is very common; nausea and dizziness are also reported. Kidney problems and neurological effects, such as confusion or hallucinations, are more likely with impaired kidney function or excessive exposure. The current UK information includes warnings about severe skin reactions, including DRESS and acute generalised exanthematous pustulosis. A spreading rash with fever, facial swelling, mouth ulcers, skin peeling or blisters needs immediate medical attention. Anyone with a previous severe reaction to valaciclovir or aciclovir should tell the prescriber.

Interactions and special circumstances

Medicines that can damage the kidneys, including tacrolimus, ciclosporin, methotrexate and certain antibiotics, require particular caution and monitoring. Cimetidine and probenecid can reduce aciclovir clearance; their importance depends on exposure and kidney function. These are review prompts, not instructions to stop essential treatment. Adequate hydration matters, particularly in people at risk of dehydration, but any prescribed fluid restriction must be discussed rather than ignored. Older adults and patients with kidney impairment may need a different prescription. Pregnancy and breastfeeding require a benefit-risk discussion; the word antiviral does not itself establish safety for an individual.

Sources

• GSK: Valtrex 500 mg tablets — UK SmPC — Text revised 18 June 2026
• GSK: Valtrex film-coated tablets — UK patient leaflet — Patient leaflet listed on emc 30 June 2026; checked 30 October 2026

Source check: 30 October 2026. This records a source check, not a clinical review by a doctor or pharmacist. Follow the leaflet for the exact product supplied to you.