Aciclovir

Guanosine Analogue·Infectious Diseases - Antivirals

HSV encephalitis, genital herpes, herpes zoster, varicella (chickenpox) in immunocompromised

Authority requiredPBSANTIVIRALZovirax200 mg tablet+2

Max Dose

Weight Based IV

Half-life

2-3 h

Renal Toxicity

CRYSTALS

Bioavailability

POOR (15%)

Rapid Summary

Overview

The foundational anti-herpetic antiviral. Highly effective against HSV and VZV. Oral formulation has terrible bioavailability, requiring frequent dosing, but IV formulation is life-saving for CNS infections.

Maximum Dose

Max 800 mg 5 times a day (PO for shingles). IV doses are 10 mg/kg q8h.

Clinical Focus

IV Aciclovir rapidly crystallizes in the renal tubules, causing severe Acute Kidney Injury. Aggressive IV hydration is mandatory.

Bottom Line

Aciclovir is the first-line antiviral for HSV and VZV infections, but requires adequate hydration to prevent crystalline nephropathy and dose adjustment in renal impairment.

Formulation & Access

Brand Names

Zovirax

Oral Routes

Tablets (200 mg, 800 mg).

Parenteral

Ampoules for IV infusion.

Prescribing & PBS

Authority Required (PBS) for certain indications.

Indications & Use

Primary

PBSTGA

HSV encephalitis, genital herpes, herpes zoster, varicella (chickenpox) in immunocompromised.

Clinical Place

IV is the absolute gold standard for suspected viral encephalitis. PO has largely been replaced by Valaciclovir for convenience.

Quick reference

Class & Role

Guanosine Analogue — The foundational anti-herpetic antiviral.

Route / Formulation

Tablets (200 mg, 800 mg). (Zovirax)

Usual Dose & Max

IV 10 mg/kg q8h (Run over 1 hour to prevent crystallization). Max 800 mg 5 times a day (PO for shingles). IV doses are 10 mg/kg q8h.

Key Indication Doses

HSV Encephalitis: IV 10 mg/kg q8h (Run over 1 hour to prevent crystallization). Genital Herpes / Cold Sores: PO 200 mg 5 times a day, or 400 mg TDS. Herpes Zoster (Shingles): PO 800 mg 5 times a day for 7 days. Renal Impairment: Extremely strict dose reduction required if eGFR < 50 to prevent fatal neurotoxicity.

Best Uses

Aciclovir is the first-line antiviral for HSV and VZV infections, but requires adequate hydration to prevent crystalline nephropathy and dose adjustment in renal impairment.

Avoid / Cautions

Previous severe hypersensitivity. Pregnancy Category B3 (Extensive data shows it is safe and often required for active genital herpes near term).

Key Risks

Renal: Acute Kidney Injury due to intratubular crystal precipitation (especially if dehydrated or pushed IV too fast). Neurological: Encephalopathy, tremors, seizures, coma (Occurs when the drug accumulates in renal failure and crosses into the brain). Tissue: Severe phlebitis and necrosis if IV fluid extravasates (pH is highly alkaline).

Key Interactions

Concurrent nephrotoxic drugs (NSAIDs, Aminoglycosides, Tazocin) exponentially increase AKI risk.

Monitoring

Daily U&E and eGFR while on IV therapy. Ensure the patient receives at least 1L of IV fluids alongside the infusion to flush the kidneys and prevent crystals.

Clinical Pearl

Because PO Aciclovir requires the patient to wake up and take pills 5 times a day, compliance is terrible. Valaciclovir is a prodrug that converts to Aciclovir in the gut, providing 3-5x higher blood levels and allowing BD or TDS dosing. Switch if possible.

Access

Authority requiredZovirax200 mg tablet

Brand: Zovirax
PBS status: Authority required
Formulation: Tablets (200 mg, 800 mg)

Aciclovir

Guanosine Analogue·Infectious Diseases - Antivirals

HSV encephalitis, genital herpes, herpes zoster, varicella (chickenpox) in immunocompromised

Authority requiredPBSANTIVIRALZovirax200 mg tablet+2

Max Dose

Weight Based IV

Half-life

2-3 h

Renal Toxicity

CRYSTALS

Bioavailability

POOR (15%)

Rapid Summary

Overview

Maximum Dose

Max 800 mg 5 times a day (PO for shingles). IV doses are 10 mg/kg q8h.

Clinical Focus

IV Aciclovir rapidly crystallizes in the renal tubules, causing severe Acute Kidney Injury. Aggressive IV hydration is mandatory.

Bottom Line

Aciclovir is the first-line antiviral for HSV and VZV infections, but requires adequate hydration to prevent crystalline nephropathy and dose adjustment in renal impairment.

Formulation & Access

Brand Names

Zovirax

Oral Routes

Tablets (200 mg, 800 mg).

Parenteral

Ampoules for IV infusion.

Prescribing & PBS

Authority Required (PBS) for certain indications.

Indications & Use

Primary

PBSTGA

HSV encephalitis, genital herpes, herpes zoster, varicella (chickenpox) in immunocompromised.

Clinical Place

IV is the absolute gold standard for suspected viral encephalitis. PO has largely been replaced by Valaciclovir for convenience.

Quick reference

Class & Role

Guanosine Analogue — The foundational anti-herpetic antiviral.

Route / Formulation

Tablets (200 mg, 800 mg). (Zovirax)

Usual Dose & Max

IV 10 mg/kg q8h (Run over 1 hour to prevent crystallization). Max 800 mg 5 times a day (PO for shingles). IV doses are 10 mg/kg q8h.

Key Indication Doses

Best Uses

Aciclovir is the first-line antiviral for HSV and VZV infections, but requires adequate hydration to prevent crystalline nephropathy and dose adjustment in renal impairment.

Avoid / Cautions

Previous severe hypersensitivity. Pregnancy Category B3 (Extensive data shows it is safe and often required for active genital herpes near term).

Key Risks

Key Interactions

Concurrent nephrotoxic drugs (NSAIDs, Aminoglycosides, Tazocin) exponentially increase AKI risk.

Monitoring

Daily U&E and eGFR while on IV therapy. Ensure the patient receives at least 1L of IV fluids alongside the infusion to flush the kidneys and prevent crystals.

Clinical Pearl

Access

Authority requiredZovirax200 mg tablet

Brand: Zovirax
PBS status: Authority required
Formulation: Tablets (200 mg, 800 mg)