Acyclovir Equivalent Dosing for Valacyclovir 1000mg TID
For patients taking valacyclovir 1000mg three times daily, the equivalent acyclovir dosage is 800mg five times daily. 1
Rationale for Dosing Conversion
Valacyclovir is a prodrug that is rapidly converted to acyclovir in the body. The bioavailability of acyclovir from valacyclovir is significantly higher than from oral acyclovir itself 2. This improved bioavailability allows for less frequent dosing while maintaining therapeutic acyclovir levels.
When converting from valacyclovir to acyclovir, several factors must be considered:
- Valacyclovir has approximately 3-5 times greater bioavailability than acyclovir 3
- Valacyclovir 1000mg provides similar systemic exposure to acyclovir 800mg, but with different dosing frequencies
- The CDC guidelines recommend acyclovir 800mg five times daily as an equivalent treatment option 1
Clinical Applications
The appropriate dosing depends on the indication being treated:
For Genital Herpes:
- First-episode treatment: Acyclovir 400mg three times daily for 5 days, or 200mg five times daily for 5 days, or 800mg twice daily for 5 days 1
- Recurrent episodes: Acyclovir 800mg twice daily for 5 days 1
For Severe Disease:
- Intravenous acyclovir 5-10 mg/kg body weight every 8 hours for 5-7 days 4
For Immunocompromised Patients:
- Higher doses may be required: Acyclovir 400mg orally three to five times daily 4
Important Considerations
Renal Function
- Dosage adjustment is required in patients with renal impairment 5, 6
- Acyclovir and its metabolites are excreted primarily by the kidney via glomerular filtration and tubular secretion 6
Administration
- Acyclovir requires more frequent administration (5 times daily) compared to valacyclovir (3 times daily)
- This more frequent dosing may affect patient adherence
Potential Adverse Effects
- Both medications are generally well tolerated
- Most common side effects include headache, nausea, and abdominal pain
- Crystalluria is a potential concern with high-dose or bolus intravenous administration 6
Special Populations
HIV-Infected Patients
- Higher doses may be required: Acyclovir 400mg three to five times daily 4
- For severe cases: Acyclovir 5 mg/kg IV every 8 hours 4
Pregnancy
- The safety of systemic acyclovir therapy in pregnant women should be carefully considered 4
Remember that the more frequent dosing schedule of acyclovir (5 times daily) compared to valacyclovir (3 times daily) may impact patient adherence, which could affect treatment outcomes. However, from a bioavailability perspective, acyclovir 800mg five times daily is the appropriate equivalent to valacyclovir 1000mg three times daily.