Valaciclovir

Prodrug of Aciclovir·Infectious Diseases - Antivirals

Herpes zoster (shingles), genital herpes, cold sores (HSV-1), CMV prophylaxis post-transplant

Authority requiredPBSANTIVIRALValtrex, Valtrex Suppression500 mg tablet+2

Max Dose

3000 mg/day

Half-life

3 h

Bioavailability

HIGH (55%)

Renal Tox

HIGH RISK

Rapid Summary

Overview

L-valyl ester prodrug of Aciclovir. Provides 3-5 times higher blood levels than oral aciclovir, allowing for massively improved patient compliance (TDS vs 5-times-daily dosing).

Maximum Dose

Max 3000 mg/day (e.g., 1000 mg TDS for Shingles).

Clinical Focus

Heavily dependent on renal clearance. Failure to reduce the dose in CKD/elderly will cause severe, irreversible neurotoxicity.

Bottom Line

Valaciclovir is the oral prodrug of aciclovir with better bioavailability for HSV and VZV, but still requires renal dose adjustment and adequate hydration to prevent crystalluria.

Formulation & Access

Brand Names

Valtrex, Valtrex Suppression

Oral Routes

Tablets (500 mg).

Prescribing & PBS

Authority Required (PBS).

Indications & Use

Primary

PBSTGA

Herpes zoster (shingles), genital herpes, cold sores (HSV-1), CMV prophylaxis post-transplant.

Clinical Place

The absolute first-line oral antiviral for VZV and HSV. Has largely rendered oral Aciclovir obsolete.

Quick reference

Class & Role

Prodrug of Aciclovir — L-valyl ester prodrug of Aciclovir.

Route / Formulation

Tablets (500 mg). (Valtrex, Valtrex Suppression)

Usual Dose & Max

PO 1000 mg TDS for 7 days. (Must start within 72 hours of rash onset). Max 3000 mg/day (e.g., 1000 mg TDS for Shingles).

Key Indication Doses

Herpes Zoster (Shingles): PO 1000 mg TDS for 7 days. (Must start within 72 hours of rash onset). Genital Herpes (Initial): PO 500 mg BD for 5-10 days. Genital Herpes (Suppression): PO 500 mg OD (or 250 mg BD). Renal Impairment (Shingles): eGFR 30-50: 1000 mg BD. eGFR 10-30: 1000 mg OD. eGFR < 10: 500 mg OD.

Best Uses

Valaciclovir is the oral prodrug of aciclovir with better bioavailability for HSV and VZV, but still requires renal dose adjustment and adequate hydration to prevent crystalluria.

Avoid / Cautions

Severe hypersensitivity to Valaciclovir or Aciclovir. Pregnancy Category B3 (Widely used and safe for peripartum genital herpes suppression).

Key Risks

Neurological: Encephalopathy, agitation, hallucinations, coma, seizures (Occurs when the drug accumulates in unadjusted renal failure). Renal: Acute Kidney Injury (AKI) due to intratubular crystal precipitation, especially if the patient is dehydrated. Gastrointestinal: Mild nausea, headache.

Key Interactions

Nephrotoxic drugs (NSAIDs, ACEi, Diuretics) increase the risk of crystal nephropathy. Encourage heavy oral hydration.

Monitoring

Check eGFR before charting the massive 1000 mg TDS Shingles dose. This dose in an 85-year-old is a guaranteed neurotoxic overdose. Instruct the patient to drink 2-3 Litres of water daily while on the 7-day high-dose course to flush the kidneys.

Clinical Pearl

For Shingles, the virus actively replicates for about 3 days. Giving Valaciclovir on Day 5 of the rash does nothing to heal the skin or prevent post-herpetic neuralgia; it just exposes the patient to kidney toxicity. Only prescribe if the rash is fresh (<72h) or actively blistering.

Access

Authority requiredValtrex, Valtrex Suppression500 mg tablet

Brand: Valtrex, Valtrex Suppression
PBS status: Authority required
Formulation: Tablets (500 mg)

Valaciclovir

Prodrug of Aciclovir·Infectious Diseases - Antivirals

Herpes zoster (shingles), genital herpes, cold sores (HSV-1), CMV prophylaxis post-transplant

Authority requiredPBSANTIVIRALValtrex, Valtrex Suppression500 mg tablet+2

Max Dose

3000 mg/day

Half-life

3 h

Bioavailability

HIGH (55%)

Renal Tox

HIGH RISK

Rapid Summary

Overview

L-valyl ester prodrug of Aciclovir. Provides 3-5 times higher blood levels than oral aciclovir, allowing for massively improved patient compliance (TDS vs 5-times-daily dosing).

Maximum Dose

Max 3000 mg/day (e.g., 1000 mg TDS for Shingles).

Clinical Focus

Heavily dependent on renal clearance. Failure to reduce the dose in CKD/elderly will cause severe, irreversible neurotoxicity.

Bottom Line

Valaciclovir is the oral prodrug of aciclovir with better bioavailability for HSV and VZV, but still requires renal dose adjustment and adequate hydration to prevent crystalluria.

Formulation & Access

Brand Names

Valtrex, Valtrex Suppression

Oral Routes

Tablets (500 mg).

Prescribing & PBS

Authority Required (PBS).

Indications & Use

Primary

PBSTGA

Herpes zoster (shingles), genital herpes, cold sores (HSV-1), CMV prophylaxis post-transplant.

Clinical Place

The absolute first-line oral antiviral for VZV and HSV. Has largely rendered oral Aciclovir obsolete.

Quick reference

Class & Role

Prodrug of Aciclovir — L-valyl ester prodrug of Aciclovir.

Route / Formulation

Tablets (500 mg). (Valtrex, Valtrex Suppression)

Usual Dose & Max

PO 1000 mg TDS for 7 days. (Must start within 72 hours of rash onset). Max 3000 mg/day (e.g., 1000 mg TDS for Shingles).

Key Indication Doses

Best Uses

Valaciclovir is the oral prodrug of aciclovir with better bioavailability for HSV and VZV, but still requires renal dose adjustment and adequate hydration to prevent crystalluria.

Avoid / Cautions

Severe hypersensitivity to Valaciclovir or Aciclovir. Pregnancy Category B3 (Widely used and safe for peripartum genital herpes suppression).

Key Risks

Key Interactions

Nephrotoxic drugs (NSAIDs, ACEi, Diuretics) increase the risk of crystal nephropathy. Encourage heavy oral hydration.

Monitoring

Clinical Pearl

Access

Authority requiredValtrex, Valtrex Suppression500 mg tablet

Brand: Valtrex, Valtrex Suppression
PBS status: Authority required
Formulation: Tablets (500 mg)