- Kidney failure: This drug may cause your kidneys to stop working. Tell your doctor if you have any kidney problems before taking this medication.
- Low red blood cells and platelets: This drug may cause thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS). These conditions cause dangerously low levels of red blood cells and platelets in your body. This may be fatal (cause death). Symptoms can include fatigue and low energy.
- Sexual contact: You shouldn’t have sexual contact with your partner when you have signs of a genital herpes outbreak. This drug does not cure herpes infections. It may help lower the chance of spreading herpes to your partner. However, even with safe sex practices, it’s still possible to spread genital herpes. Talk to your doctor for information about safe sex practices.
What is acyclovir?
Acyclovir oral tablet is a prescription drug that’s available as the brand-name drug Zovirax. It’s also available as a generic drug. Generic drugs usually cost less. In some cases, they may not be available in every strength or form as the brand-name version.
Acyclovir also comes as an oral capsule, oral suspension, buccal tablet, topical cream, and topical ointment. In addition, acyclovir is available as an intravenous drug, which is only given by a healthcare provider.
This drug may be used as part of a combination therapy. This means you may need to take it with other medications.
Why it's used
Acyclovir is used to treat viral infections. These include varicella-zoster (shingles), genital herpes, and chickenpox.
This drug doesn’t cure herpes infections. The herpes virus can stay in your body for a long time and cause symptoms again later.
How it works
Acyclovir belongs to a class of drugs called antivirals. A class of drugs is a group of medications that work in a similar way. These drugs are often used to treat similar conditions.
Acyclovir works by lowering the ability of the herpes virus to multiply in your body. This treats the symptoms of your infection. However, this drug doesn’t cure herpes infections. Herpes infections include cold sores, chickenpox, shingles, or genital herpes. Even with this drug, the herpes virus may still live in your body. Your symptoms may occur again later even after the symptoms of your current infection go away.
Acyclovir side effects
Acyclovir oral tablet doesn’t cause drowsiness but it can cause other side effects.
More common side effects
Some of the more common side effects of acyclovir oral tablet include:
Serious side effects
Call your doctor right away if you have serious side effects. Call 911 if your symptoms feel life-threatening or if you think you’re having a medical emergency. Serious side effects and their symptoms can include the following:
- Unusual changes in your mood or behavior. Symptoms can include:
- aggressive behavior
- unsteady or shaky movements
- trouble speaking
- hallucinations (seeing or hearing something that isn’t there)
- coma (being unconscious for a long time)
- Decrease in your red blood cells and platelets. Symptoms can include:
- Liver problems
- Muscle pain
- Skin reactions. Symptoms can include:
- hair loss
- breaking or loosening of skin
- Stevens-Johnson syndrome. This is a rare, allergic skin reaction.
- Changes in your vision
- Kidney failure. Symptoms can include:
- kidney or flank pain (pain in your side and back)
- blood in your urine
- Allergic reaction. Symptoms can include:
- trouble breathing
- swelling of your throat or tongue
Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we cannot guarantee that this information includes all possible side effects. This information is not a substitute for medical advice. Always discuss possible side effects with a healthcare provider who knows your medical history.
Acyclovir may interact with other medications
An interaction is when a substance changes the way a drug works. This can be harmful or prevent the drug from working well. To help prevent interactions, your doctor should manage all of your medications carefully. Be sure to tell your doctor about all medications, vitamins, or herbs you’re taking.
To find out how this drug might interact with something else you’re taking, talk to your doctor or pharmacist.
Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs interact differently in each person, we cannot guarantee that this information includes all possible interactions. This information is not a substitute for medical advice. Always speak with your healthcare provider about possible interactions with all prescription drugs, vitamins, herbs and supplements, and over-the-counter drugs that you are taking.
This drug comes with several warnings.
Acyclovir can cause a severe allergic reaction. Symptoms can include:
- trouble breathing
- swelling of your throat or tongue
Call 911 or go to the nearest emergency room if you develop these symptoms. Don’t take this drug again if you’ve ever had an allergic reaction to it. Taking it again could be fatal (cause death).
Warnings for certain groups
For people with kidney problems: If you have kidney problems or a history of kidney disease, you may not be able to clear this drug from your body well. This may increase the levels of this drug in your body and cause more side effects.
This medication may also decrease your kidney function. This means your kidney disease may get worse. Your doctor will adjust your dose depending on how well your kidneys are working.
For pregnant women: Acyclovir is a category B pregnancy drug. That means two things:
- Studies of the drug in pregnant animals have not shown a risk to the fetus.
- There aren’t enough studies done in pregnant women to show if the drug poses a risk to the fetus.
Talk to your doctor if you’re pregnant or planning to become pregnant. This drug should be used only if the potential benefit justifies the potential risk to the fetus.
Call your doctor right away if you become pregnant while taking this drug.
For women who are breastfeeding: Acyclovir may pass into breast milk and may cause side effects in a child who is breastfed. Talk to your doctor if you breastfeed your baby. You may need to decide whether to stop breastfeeding or stop taking this medication.
For seniors: The kidneys of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, more of a drug stays in your body for a longer time. This raises your risk of side effects.
For children: This drug hasn’t been studied in children younger than 2 years.
How to take acyclovir
This dosage information is for acyclovir oral tablet. All possible dosages and drug forms may not be included here. Your dosage, drug form, and how often you take the drug will depend on:
- your age
- the condition being treated
- how severe your condition is
- other medical conditions you have
- how you react to the first dose
Forms and strengths
- Form: oral tablet
- Strengths: 400 mg, 800 mg
- Form: oral tablet
- Strengths: 400 mg, 800 mg
Dosage for shingles, genital herpes, or chickenpox
Adult dosage (ages 18–64 years)
- Shingles: 800 mg taken every 4 hours, five times per day for 7–10 days
- Genital herpes:
- Initial treatment: 200 mg taken every 4 hours, five times per day for 10 days
- Prevention of recurrent herpes: Take 400 mg twice per day, every day for up to 12 months. Your doctor will decide how long you should take this drug to avoid a flare-up of the infection.
- Reinfection (flare-up of the infection): Take 200 mg every 4 hours, five times per day for 5 days. You should take this drug as soon as the first signs of a flare-up appear.
- Chickenpox: Take 800 mg four times per day for 5 days. Start this drug as soon as your first symptom of chickenpox appears. It isn’t known if this drug is effective if you start it more than 24 hours after the first sign of chickenpox.
Child dosage (ages 2–17 years)
- Children who weigh 40 kg (88 lbs.) or less: 20 mg/kg of body weight, given four times per day for 5 days
- Children who weigh more than 40 kg: 800 mg four times per day for 5 days
Start this drug as soon as the first symptom of chickenpox appears. It isn’t known if this drug is effective if your child starts it more than 24 hours after the first sign of chickenpox.
Child dosage (ages 0–1 years)
It hasn’t been confirmed that acyclovir is safe and effective for children younger than 2 years.
Senior dosage (ages 65 years and older)
The kidneys of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, more of a drug stays in your body for a longer time. This increases your risk of side effects.
Your doctor may start you on a lowered dose or a different medication schedule. This can help keep levels of this drug from building up too much in your body.
Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we cannot guarantee that this list includes all possible dosages. This information is not a substitute for medical advice. Always to speak with your doctor or pharmacist about dosages that are right for you.
Take as directed
Acyclovir oral tablet is used for short-term treatment of genital herpes, shingles, and chicken pox. It’s used for long-term treatment of recurring genital herpes. This drug comes with serious risks if you don’t take it as prescribed.
If you stop taking the drug suddenly or don’t take it at all: The symptoms of your infection may not get better or may get worse.
If you miss doses or don’t take the drug on schedule: Your medication may not work as well or may stop working completely. If you’re taking this drug to prevent flare-ups of your infection, a certain amount needs to be in your body at all times. You shouldn’t stop taking this drug without talking to your doctor first.
What to do if you miss a dose: Take your dose as soon as you remember. But if you remember just a few hours before your next scheduled dose, take only one dose. Never try to catch up by taking two doses at once. This could result in dangerous side effects.
If you take too much: You could have dangerous levels of the drug in your body and experience more severe side effects. If you think you’ve taken too much of this drug, call your doctor or local poison control center. If your symptoms are severe, call 911 or go to the nearest emergency room right away.
How to tell if the drug is working: The symptoms of your infection will get better.
Important considerations for taking acyclovir
Keep these considerations in mind if your doctor prescribes acyclovir oral tablet for you.
- Take this drug at the time(s) recommended by your doctor.
- You can take acyclovir with or without food. Taking it with food may help reduce upset stomach.
- Do not cut or crush this medication.
- Not every pharmacy stocks this drug. When filling your prescription, be sure to call ahead to make sure your pharmacy carries it.
- Store this drug at room temperature. Keep it between 59°F and 77°F (15°C and 25°C).
- Keep it away from light.
- Don’t store this medication in moist or damp areas, such as bathrooms.
A prescription for this medication is refillable. You should not need a new prescription for this medication to be refilled. Your doctor will write the number of refills authorized on your prescription.
When traveling with your medication:
- Always carry your medication with you. When flying, never put it into a checked bag. Keep it in your carry-on bag.
- Don’t worry about airport x-ray machines. They can’t hurt your medication.
- You may need to show airport staff the pharmacy label for your medication. Always carry the original prescription-labeled box with you.
- Don’t put this medication in your car’s glove compartment or leave it in the car. Be sure to avoid doing this when the weather is very hot or very cold.
You and your doctor should monitor certain health issues. This can help make sure you stay safe while you take this drug. These issues include:
- Kidney function. Your doctor may do blood tests to check how well your kidneys are working. If your kidneys aren’t working well, your doctor may lower your dose of this drug.
- Mental health and behavioral problems. You and your doctor should watch for any unusual changes in your behavior and mood. This drug can cause new mental health and behavior problems. It can also worsen problems you already have.
You should drink plenty of water to stay hydrated. This drug can harm your kidneys if you don’t stay well hydrated.
Acyclovir can make your skin more sensitive to the sun. This increases your risk of sunburn. Avoid the sun if you can. If you can’t, be sure to wear protective clothing and apply sunscreen.
Many insurance companies require a prior authorization for this drug. This means your doctor will need to get approval from your insurance company before your insurance company will pay for the prescription.
Are there any alternatives?
There are other drugs available to treat your condition. Some may be better suited for you than others. Talk to your doctor about other drug options that may work for you.
Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up-to-date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or other healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.