Valacyclovir: uses, dosing, side effects & brands

VALTREX (valacyclovir hydrochloride) is the hydrochloride salt of the L ‑valyl ester of the antiviral drug acyclovir. VALTREX tablets are for oral administration. Each tablet contains 556.2 mg or 1.112 grams of valacyclovir hydrochloride equivalent to 500 mg or 1 gram of valacyclovir, respectively, and the inactive ingredients carnauba wax, colloidal silicon dioxide, crospovidone, FD&C Blue No. 2 Lake, hypromellose, magnesium stearate, microcrystalline cellulose, polyethylene glycol, polysorbate 80, povidone, and titanium dioxide. The blue, film‑coated tablets are printed with edible white ink.

The FDA classifies valacyclovir as a herpes simplex virus nucleoside analog dna polymerase inhibitor. If you are checking whether it is safe to combine with something else, the class is what matters — two drugs from the same class usually should not be stacked.

It depends on the medicine. We check it against the FDA labels rather than guessing: our interaction checker searches each drug's own label for the other and quotes what it says, naming the section it came from. Run valacyclovir against whatever else you take — and remember that a label not naming a drug is not the same as that combination being safe.

Across the brands we track, valacyclovir is currently marketed as tablet, per the FDA's National Drug Code Directory. Each form is dosed differently — follow the label for the exact product you were prescribed.

We do not currently list a generic-labelled valacyclovir product. That does not always mean none exists — it means none appears under a generic name in the FDA data we track. Ask your pharmacist.

The FDA's Enforcement database lists 1 recall record whose product description mentions valacyclovir. The most recent: Valacyclovir Tablets USP (Apr 25, 2024). A recall applies to specific lots, not to the drug as a whole — check the record for the affected lot numbers.

Headache, nausea, and abdominal pain — those are the reactions the FDA label reports in more than 10% of adults in at least one of its indications, and headache was the only one over 10% in patients under 18. Most people taking a short course for a cold sore, genital herpes outbreak, or shingles get through it with nothing worse than a headache. Dizziness and fatigue also appear on the label. These generally do not require stopping the medicine; take doses with a full glass of water and food if your stomach is unsettled.

Go to the ER for new confusion, agitation, hallucinations, slurred speech, unsteadiness, or a seizure. The FDA label carries a specific warning for central nervous system reactions — including agitation, hallucinations, confusion, delirium, seizures, and encephalopathy — and notes elderly patients are more likely to have them. Also seek urgent care for: passing much less urine, swelling, or flank pain (acute renal failure is a labeled warning); a painful rash with mouth, eye, or genital sores, or a progressive severe rash (the label warns about SJS, TEN, DRESS, and AGEP and says to stop valacyclovir immediately — and it now contraindicates the drug in anyone who has previously had a severe cutaneous reaction to valacyclovir or acyclovir); or unexplained bruising, tiny red skin spots, and severe fatigue (TTP/HUS, which the label reports as sometimes fatal in patients with advanced HIV disease and in bone marrow and kidney transplant recipients taking 8 grams a day).

It can, and the mechanism tells you how to avoid it. Valacyclovir converts to acyclovir, which can crystallize in the kidney tubules when its concentration exceeds its solubility. The FDA label therefore lists inadequate hydration as one of the four situations where acute renal failure has been reported — the other three are elderly patients, people whose dose was too high for their kidney function, and people also taking nephrotoxic drugs. Practical translation: drink fluids steadily through the course, tell the prescriber about any kidney problems so the dose gets reduced, and mention regular NSAID use. The confusion and hallucinations described above usually travel with the same problem, since acyclovir accumulates when the kidneys cannot clear it.

Not dramatically, but the exposure math changes and so does the monitoring. A cold sore is treated with a one-day regimen and an outbreak with a few days; suppression means taking it every day for months or years. The labeled risks that scale with cumulative dose and duration — kidney effects and CNS effects — are the ones to watch, which is why kidney function should be rechecked periodically on long-term therapy and why the dose must be adjusted if kidney function drops. The TTP/HUS warning is anchored to very high doses (8 grams daily) in immunocompromised patients, not to standard suppressive dosing.