Most Common Side Effects of Acyclovir
Acyclovir, an antiviral used for herpes infections, most often causes mild gastrointestinal issues. Nausea affects up to 12% of users, vomiting up to 7%, and diarrhea up to 5%. Headache occurs in about 5-10% of cases, while dizziness and fatigue each hit around 2-5%.[1][2]
Side Effects by Route of Administration
Oral acyclovir leads to more nausea and diarrhea compared to topical forms. Topical cream or ointment commonly irritates the application site with burning, stinging, or itching in 10-30% of patients. Intravenous use raises risks of reversible kidney issues like elevated creatinine (5-10%) and phlebitis at the injection site.[1][3]
What Happens with Long-Term or High-Dose Use?
Extended or high-dose therapy, especially IV, increases chances of neurotoxicity (confusion, tremors, hallucinations) in 1-2% of cases, particularly in those with kidney impairment. Adjust doses for renal function to minimize this.[2][4]
Who Experiences Side Effects Most?
Elderly patients or those with reduced kidney function report higher rates of nausea, dizziness, and renal effects. Children on oral suspensions see similar GI issues but fewer headaches. Allergic reactions like rash or swelling are rare (<1%).[1][3]
How Do These Compare to Valacyclovir?
Valacyclovir, a prodrug of acyclovir, has nearly identical side effects but slightly higher nausea (15-20%) due to better absorption. Headache and dizziness rates match closely.[2][5]
[1]: Drugs.com - Acyclovir Side Effects
[2]: MedlinePlus - Acyclovir
[3]: FDA Label - Zovirax (Acyclovir)
[4]: UpToDate - Acyclovir Overview
[5]: Drugs.com - Valacyclovir Side Effects