Acyclovir and Valacyclovir interaction
Acyclovir and Valacyclovir: both prescribing labels flag this combination with the strongest language, such as a contraindication, a boxed warning, or an instruction to avoid it.
Do not combine without a prescriber's guidance. The label language below is the strongest FDA uses.
What the FDA labels say
From the Acyclovir label · effective 2026-06-26
CONTRAINDICATIONS Acyclovir tablets are contraindicated in patients who have demonstrated clinically significant hypersensitivity reaction [e.g., anaphylaxis, severe cutaneous adverse reactions (SCARs) to acyclovir, valacyclovir, or any component of the formulation (see WARNINGS and ADVERSE REACTIONS ).
Acyclovir tablets are contraindicated in patients who have developed SCARs with the use of acyclovir or valacyclovir, or any component of the formulation (see CONTRAINDICATIONS and ADVERSE REACTIONS ).
From the Valacyclovir (VALTREX) label · effective 2026-07-16
VALTREX is 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 [see Warnings and Precautions ( 5.4 ), Adverse Reactions ( 6.3 )] .
Hypersensitivity to valacyclovir (e.g., anaphylaxis), acyclovir, or any component of the formulation.
VALTREX is contraindicated in patients who have developed SCARs with the use of valacyclovir or acyclovir, or any component of the formulation [see Contraindications ( 4 ), Adverse Reactions ( 6.3 )] .
Precipitation of acyclovir in renal tubules may occur when the solubility (2.5 mg/mL) is exceeded in the intratubular fluid.
Taking more than these two? Interactions stack. Check your whole list at once; it stays in your browser.
Open in the checkerNot medical advice. Interaction Checker quotes FDA label text and NIH fact sheets. Whether an interaction matters for you depends on doses, timing, kidney and liver function, and other conditions. Confirm with a pharmacist or prescriber.