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Valaciclovir

Medication antiviral other
Aka: valacyclovir, Valtrex
Brands seen in Singapore: Valtrex, Valovir, Vaciclor
Not medical advice. Check with your doctor or pharmacist before you start, stop or change the timing of anything you take.
How to use
What it’s for
Prescribed for shingles, cold sores and genital herpes
When to take
FDA: tablets may be given without regard to meals
Take with
Water · HealthHub: regular water intake matters on it
Pros & cons
Pros
  • FDA: the cold sore course is one day, two doses
  • FDA: no known clinically significant interactions
  • HealthHub: taken with or without food
Cons
  • HealthHub: kidney problems, confusion, hallucinations
  • HealthHub: headache, nausea and rash are common
  • HealthHub: sun-exposed skin can react
Sources
  1. HSA — Listing of Registered Therapeutic Products (data.gov.sg open dataset, 5,511 rows, cached in full and filtered locally) · read 2026-08-27
    what it says
    “Only 3 valaciclovir rows exist, all 'Prescription Only' and all 500 mg tablets — SIN08229P VALTREX TABLET 500 mg, SIN14878P VALOVIR 500, SIN14207P Vaciclor Tablet 500 mg; ATC J05AB11.”
  2. HealthHub (Pharmaceutical Society of Singapore) — Valaciclovir: what is this medication for · read 2026-08-27
    what it says
    “This medication is also known as 'valacyclovir'. It is an antiviral medication used to treat shingles, susceptible viral infections of the skin and genitals, cold sores, prevent viral infections after organ transplants, treat and prevent viral infections of the eye.”
  3. HealthHub — Valaciclovir: how should I take this medication · read 2026-08-27
    what it says
    “You may take this medication with or without food. Swallow the tablets whole with a drink of water. It is very important that you drink water regularly while you are taking the medication.”
  4. HealthHub — Valaciclovir: what precautions should I take · read 2026-08-27
    what it says
    “You are allergic to this medication or any of the other ingredients … Do not drive, use machinery or do anything else that could be dangerous if you are dizzy or are not alert.”
  5. HealthHub — Valaciclovir: common side effects · read 2026-08-27
    what it says
    “Headache; Rash, skin itchiness; Nausea, vomiting, diarrhoea, abdominal pain; Skin reaction after exposure to sunlight; Feeling unwell; Dizziness”
  6. HealthHub — Valaciclovir: rare but serious side effects · read 2026-08-27
    what it says
    “Kidney problem: Unable to pass urine, change in urine volume, blood in urine; Feeling confused, change in behaviour, mood changes; Seeing or hearing things that are not present; Slow, slurred speech; Seizures, tremors; Unsteadiness when walking”
  7. HealthHub — Valaciclovir: what food or medication should I avoid · read 2026-08-27
    what it says
    “This medication may reduce the effects of certain vaccines and should be avoided. Other medications may increase the risks of this medication's kidney-related side effects. You should therefore avoid taking these medications together.”
  8. US FDA label — valacyclovir tablets, section 2 Dosage and Administration (adult), via openFDA drug/label.json · read 2026-08-27
    what it says
    “Valacyclovir tablets may be given without regard to meals … Cold Sores 2 grams every 12 hours for 1 day … Herpes Zoster 1 gram 3 times daily for 7 days”
  9. US FDA label — valacyclovir tablets, section 2.1 genital herpes regimens, via openFDA drug/label.json · read 2026-08-27
    what it says
    “Genital Herpes Initial episode 1 gram twice daily for 10 days; Recurrent episodes 500 mg twice daily for 3 days; Suppressive therapy Immunocompetent patients 1 gram once daily”
  10. US FDA label — valacyclovir tablets, section 2.2 Pediatric Dosage, via openFDA drug/label.json · read 2026-08-27
    what it says
    “Chickenpox (aged 2 to less than 18 years) 20 mg/kg 3 times daily for 5 days; not to exceed 1 gram 3 times daily”
  11. US FDA label — valacyclovir tablets, section 4 Contraindications, via openFDA drug/label.json · read 2026-08-27
    what it says
    “Valacyclovir tablets are contraindicated in patients who have had a demonstrated clinically significant hypersensitivity reaction [e.g., anaphylaxis, severe cutaneous adverse reactions (SCARs)] to valacyclovir, acyclovir, or any component of the formulation”
  12. US FDA label — valacyclovir tablets, section 7 Drug Interactions, via openFDA drug/label.json · read 2026-08-27
    what it says
    “No clinically significant drug-drug or drug-food interactions with valacyclovir tablets are known.”
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Updated 2026-08-29. Every line above traces to a numbered source. Kozen-X is not a medical device and does not give medical advice. It lists what published sources have written down — nothing more. A pair not listed is unrecorded, not cleared. Before you start, stop or re-time anything, talk to your doctor or pharmacist.