Generic Aciclovir

Common use

Aciclovir is an antiviral drug, it is a synthetic ingredient with a similar molecular structure to purine nucleoside. Aciclovir is used to treat viral infections such as cold sores, to stop the growth of Herpes simplex virus, Varicella zoster virus (caused by chickenpox and shingles), Epstein Barr Virus (caused by glandular fever), and to a lesser extent Cytomegalovirus (CMV). It is also useful in preventing genital herpes and in preventing viral infections occurring in those with a lowered immune system. This medication may also help reduce how long pain remains after the sores heal. In addition, in people with a weakened immune system, Aciclovir can decrease the risk of the virus spreading to other parts of the body and causing serious infections.



Dosage and direction

Take this medication by mouth with or without food, usually 2 to 5 times a day as directed by your doctor. Take this medicine by mouth with a glass of water. Take your medicine at regular intervals. Do not take your medicine more often than directed. Take all of your medicine as directed even if you think your are better. If you are using the liquid form of this medication, shake the bottle well before each dose. Carefully measure the dose using a special measuring device/spoon. Do not use a household spoon because you may not get the correct dose. Dosage is based on your medical condition and response to treatment. In children, dosage is also based on weight.



Precautions

You should talk with your healthcare provider prior to taking Aciclovir if you have kidney disease, including kidney failure (renal failure), any allergies, including allergies to food, dyes, or preservatives. Let your healthcare provider know if you are pregnant or thinking of becoming pregnant, breastfeeding.

Make sure to tell your healthcare provider about all medicines you take, including prescription and non-prescription medicines, vitamins, and herbal supplements.

The medication passes through breast milk. Therefore, if you are breastfeeding or plan to start, discuss this with your healthcare provider prior to taking the drug



Contraindications

Aciclovir Injection is contraindicated for patients who develop hypersensitivity to aciclovir or valaciclovir.



Possible side effects

Side effects are potentially serious and you should report to your doctor or health care professional as soon as possible. These include, but are not limited to: allergic reactions like skin rash, itching or hives, swelling of the face, lips, or tongue, chest pain, confusion, hallucinations, tremor, dark urine, increased sensitivity to the sun, redness, blistering, peeling or loosening of the skin, including inside the mouth, seizures, trouble passing urine or change in the amount of urine, unusual bleeding or bruising, or pinpoint red spots on the skin, unusually weak or tired, yellowing of the eyes or skin. Side effects that usually do not require medical attention: diarrhea, fever, headache, nausea, vomiting stomach upset. In this way report to your doctor or health care professional if they continue or are bothersome.



Drug interactions

There are negative interactions that can occur when Aciclovir is combined with any of the drugs listed above. Phenytoin (Fosphenytoin) and Aciclovir: it may decrease the level of phenytoin in your blood, perhaps making it less effective. Your healthcare provider may need to measure the level of phenytoin in your blood (using a blood test) and adjust your dose as necessary. Probenecid can increase the level of Aciclovir in your blood, increasing your risk of acyclovir side effects. Your healthcare provider may need to decrease your acyclovir dosage to prevent this interaction from occurring. Acyclovir can increase the level of Tenofovir in your blood, potentially increasing your risk of side effects. Your healthcare provider may need to lower your tenofovir dosage to prevent drug interactions from occurring.



Missed dose

Take the missed dose as soon as you remember. If it is almost time for your next dose, skip the missed dose and take the medicine at the next regularly scheduled time. Do not take extra medicine to make up the missed dose.



Overdose

Seek emergency medical attention if you think you have used too much of this medicine. Overdose symptoms may include seizure (convulsions), hallucinations, and urinating less than usual or not at all.



Storage

Store at controlled room temperature of 15°C to 25°C (59°F to 77°F). Keep this medicine out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.



Disclaimer

We provide only general information about medications which does not cover all directions, possible drug integrations, or precautions. Information at the site cannot be used for self-treatment and self-diagnosis. Any specific instructions for a particular patient should be agreed with your health care adviser or doctor in charge of the case. We disclaim reliability of this information and mistakes it could contain. We are not responsible for any direct, indirect, special or other indirect damage as a result of any use of the information on this site and also for consequences of self-treatment.

Clinical Verification

Last Clinically Updated: August 15, 2026

Written By

Dr. Elena Vance, PharmD

Clinical Specialist in Neuropharmacology

Fact Checked By

Marcus Thorne, MS

Biomedical Data & FDA Label Verification

Medically Reviewed By

Dr. Arthur Campbell, MD

Board-Certified Psychiatrist (ABPN)