1 What is this medicine
and what is it used for?
Valaciclovir is the oral prodrug of aciclovir — after
absorption it is rapidly converted to aciclovir by intestinal and hepatic
enzymes, achieving bioavailability 3–5 times higher than oral aciclovir.
Aciclovir is then selectively activated in virus-infected cells, where it
inhibits viral DNA polymerase, blocking herpesvirus replication.
Valtrex is used to treat and suppress infections caused by
herpes simplex virus (HSV) and varicella-zoster virus (VZV):
• Herpes zoster (shingles): treatment
to reduce severity, duration and pain — 1 g three times daily for 7 days.
• Genital herpes (HSV-2): first episode
treatment — 500 mg twice daily for 10 days.
• Recurrent genital herpes: episodic
treatment — 500 mg twice daily for 3–5 days (at the first sign or symptom).
• Suppression of recurrent genital
herpes: 500 mg once daily (long-term suppressive therapy).
• Prevention of cytomegalovirus (CMV)
disease post-transplant (high-dose valaciclovir): 2 g four times daily.
• Cold sores (herpes labialis): 2 g
twice daily for one day (single-day treatment).
2 How to take this
medicine
Take each dose with a full glass of water — adequate
hydration is important to prevent crystallisation in the kidneys
(crystalluria). May be taken with or without food. The dose and duration vary
by indication — take exactly as prescribed. For episodic genital herpes,
starting treatment at the very first sign (tingling, itching, prodrome) gives
the best outcome.
|
Drink at least 1.5
litres of water per day while taking valaciclovir — especially important in
elderly patients and in those with reduced kidney function. For recurrent genital
herpes: keep a supply at home and start treatment at the very first warning
sign (tingling or itching), even before a sore appears. 10-tablet pack: used
for short 5-day courses. 42-tablet pack: used for 7-day shingles treatment
(3x daily x 7 days = 21 tablets) or 6-week suppressive therapy (500mg OD x 42
days). |
3 Possible side effects
|
Frequency |
Side Effect |
What to Do |
|
Very Common (>10%) |
Headache |
Usually mild; take
paracetamol if needed. |
|
Very Common (>10%) |
Nausea |
Take with food;
usually improves within a few days. |
|
Common (1–10%) |
Dizziness |
Avoid driving if
affected. |
|
Common (1–10%) |
Abdominal pain /
vomiting |
Ensure good fluid
intake. |
|
Common (1–10%) |
Elevated liver enzymes |
Usually transient;
monitoring if pre-existing liver disease. |
|
Uncommon |
Renal impairment
(acute kidney injury) |
Ensure excellent
hydration; dose adjustment required if pre-existing renal impairment. |
|
Rare (with high doses
/ renal impairment) |
Neurological effects:
confusion, hallucinations, agitation, seizures, encephalopathy |
Seek immediate medical
attention — usually related to excessive drug levels from inadequate dose
adjustment in renal failure. |
|
Rare |
Thrombotic
thrombocytopenic purpura / haemolytic uraemic syndrome (TTP/HUS) — mainly in
severely immunocompromised patients at high doses |
Emergency: report
fever, neurological symptoms, anaemia, and low platelets urgently. |
4 Who should not take
this medicine
|
Cautions with Valaciclovir: Renal impairment: dose
adjustment is MANDATORY — valaciclovir is renally excreted; accumulation
causes neurotoxicity. Always check eGFR before prescribing. Elderly patients:
renal function declines with age; assume dose adjustment is needed and ensure
excellent hydration. Pregnancy: generally
considered safe when benefit outweighs risk (Category B); widely used for
genital herpes in pregnancy. Discuss with obstetrician. Breastfeeding:
aciclovir (active metabolite) passes into breast milk; generally considered
acceptable at standard doses. Known hypersensitivity
to valaciclovir, aciclovir, or any excipient. |
5 Drug interactions
• Nephrotoxic drugs (ciclosporin,
tacrolimus, NSAIDs, aminoglycosides, IV contrast): additive renal impairment —
monitor renal function.
• Probenecid / cimetidine: reduce renal
tubular secretion of aciclovir — increased plasma levels; dose adjustment may
be needed.
• Mycophenolate mofetil (in transplant
patients): both compete for renal tubular secretion — monitor both drug levels.
6 Storage
Store at room temperature below 30°C. Keep in original
blister packaging. Keep out of reach of children. Do not use after expiry date.
7 Prescription
requirement
|
PRESCRIPTION ONLY
MEDICINE (POM) — GP, dermatologist, GUM specialist, or infectious diseases
prescription. Note: In some
countries, single-day cold sore treatment may be available OTC; check local
regulations. For suppressive therapy: annual review of renal function and
continued indication is recommended. |
8 Guidance for patients
& caregivers
For genital herpes suppression: daily valaciclovir
significantly reduces the frequency and severity of outbreaks and also reduces
— but does not eliminate — the risk of transmitting HSV to partners. The risk
of transmission is further reduced (by approximately 50% additional) when
combined with consistent condom use.
For shingles: starting valaciclovir within 72 hours of rash
onset gives the best chance of reducing pain severity and duration, including
post-herpetic neuralgia. If you suspect shingles (a painful one-sided
blistering rash), contact your doctor without delay.
Stay well hydrated while taking valaciclovir — drinking
plenty of water helps protect your kidneys and prevents the rare complication
of crystalluria.
9 Pharmacist &
prescriber notes
Dose adjustment by renal function: CrCl > 50 mL/min —
standard doses; CrCl 30–49 — reduce herpes zoster dose to 1 g BD; CrCl 10–29 —
1 g OD; CrCl < 10 / haemodialysis — 500 mg OD (post-dialysis on dialysis
days). For genital herpes suppression in CrCl < 30: 500 mg every 48 hours.
Neurotoxicity (confusion, hallucinations) is almost always
related to inadequate dose adjustment in renal impairment — check eGFR in
elderly patients before and during treatment. The 10-tablet pack covers: 5-day
episodic genital herpes (500 mg BD) or single-day cold sore treatment (2 g BD =
4 tablets per day x 1 day = 4 tablets — spare remaining). The 42-tablet pack
covers: 7-day shingles (1 g TDS = 6 tablets/day x 7 days = 42 tablets exactly).
Suppressive therapy at 500 mg OD with 42-tablet pack = 6 weeks.
10 Frequently asked
questions
Does valaciclovir cure herpes?
No — valaciclovir suppresses herpes
virus replication but does not eliminate the virus from the body. The virus
remains dormant in nerve ganglia. Treatment controls outbreaks and reduces
transmission risk, but the virus can reactivate in future.
I am on suppressive therapy — do I still need to use
condoms?
Yes — daily valaciclovir reduces but
does not completely eliminate the risk of transmitting herpes to a partner.
Using condoms in addition to suppressive therapy provides the greatest
protection.
What do I do if I have kidney problems?
Tell your doctor about any kidney
disease before starting. The dose of valaciclovir must be reduced if your
kidney function is reduced, otherwise drug levels can build up and cause
neurological side effects. Your doctor will check your kidney function.
Is the 10-tablet or 42-tablet pack the right one for me?
The 10-tablet pack is typically for
short episodic treatments (e.g. 5-day genital herpes course). The 42-tablet
pack is for the 7-day shingles course (3 times daily) or 6-week suppressive
therapy at once daily. Your doctor will prescribe the appropriate pack size for
your indication.