Acyclovir: Side Effects, Uses & Monitoring
1.1 Adult Patients Cold Sores (Herpes Labialis): Valacyclovir tablets, USP are indicated for treatment of cold sores (herpes labialis).
- Data source
- FDA labeling via NIH DailyMed (label 8f8b0fb5…)
- Label version
- current
- Last reviewed
- 2026
Reported adverse reactions
Reactions listed in current FDA labeling, with the highest frequency reported across summarized placebo-controlled trials.
| Adverse reaction (as reported in labeling) | Reported frequency* |
|---|---|
| White blood cells (<0.75 x lln) | 1.5% |
| Platelet count (<100,000/mm3) | 1.5% |
| Serum creatinine (>1.5 x uln) | 0.7% |
*Highest percentage reported for the active moiety across placebo-controlled trial tables in current FDA labeling. Values reflect trial reporting, not your individual risk.
Labeled uses (from FDA prescribing information)
1.1 Adult Patients Cold Sores (Herpes Labialis): Valacyclovir tablets, USP are indicated for treatment of cold sores (herpes labialis). The efficacy of valacyclovir tablets, USP initiated after the development of clinical signs of a cold sore (e.g., papule, vesicle, or ulcer) has not been established. Genital Herpes: Initial Episode: Valacyclovir tablets, USP are indicated for treatment of the initial episode of genital herpes in immunocompetent adults. The efficacy of treatment with valacyclovir tablets, USP when initiated more than 72 hours after the onset of signs and symptoms has not been established. Recurrent Episodes: Valacyclovir tablets, USP are indicated for treatment of recurrent episodes of genital herpes in immunocompetent adults. The efficacy of treatment with valacyclovir tablets, USP when initiated more than 24 hours after the onset of signs and symptoms has not been established. Suppressive Therapy: Valacyclovir tablets, USP are indicated for chronic suppressive therapy of recurrent episodes of genital herpes in immunocompetent and in HIV-infected adults. The efficacy and safety of valacyclovir tablets, USP for the suppression of genital herpes beyond 1 year in imm…
Conditions associated with Acyclovir in labeling
Genital Herpes
A common sexually transmitted viral infection causing recurrent outbreaks of painful blisters or sores in the ...
Herpes Zoster
A painful rash (shingles) caused by reactivation of the varicella-zoster virus, often with burning pain before...
Shingles
A painful rash caused by reactivation of the varicella-zoster virus, usually appearing as a band of blisters o...
Frequently Asked Questions
What is Acyclovir used for?
FDA labeling lists the approved uses shown above under "Labeled uses." This summary is informational; only a qualified prescriber can determine whether a medication is appropriate for you.
What are the most commonly reported side effects of Acyclovir?
The table above shows adverse reactions and the highest frequencies reported in placebo-controlled trials summarized in current FDA labeling for Acyclovir. Individual risk varies.
Does Acyclovir require lab monitoring?
Monitoring needs vary. Ask your healthcare provider whether any lab tests apply while taking Acyclovir.
Where does this information come from?
All clinical facts on this page were extracted from the current FDA-registered product labeling for this ingredient, published by manufacturers through NIH DailyMed. See the source link below.
Medical disclaimer: Educational content extracted from public FDA labeling. Not medical advice. Always consult a qualified healthcare professional before starting, stopping, or changing any medication.