What Are the Side Effects of Aciclovir?

Dr Kathryn Basford

Medically reviewed by

Dr Kathryn Basford

Last reviewed: 26 Feb 2019

How to recognise and manage them

Man in a cafe researching the side effects of Aciclovir on his smart phone

Key takeaways

  • Aciclovir can cause a range of common, uncommon, and rare side effects

  • Some people are more likely to experience side effects than others

  • There are a few ways you can check if you're having aciclovir side effects

  • It's important to know whether to stop treatment and what to do in an emergency

  • Aciclovir treatment has a lot of benefits, don't let side effects get in the way of getting treated

What side effects can aciclovir give you?

Aciclovir is a drug you might be prescribed to take for certain types of viruses. It’s used for cold sores around the mouth, shingles, chickenpox and genital herpes.

Common side effects:

  • Nausea (feeling sick)
  • Vomiting
  • Diarrhea
  • Headaches

Uncommon side effects:

  • Tiredness
  • Stomach pain
  • Constipation
  • Mood changes – this might be agitation, hallucinations, confusion
  • Dizziness or drowsiness
  • Sign(s) of kidney problem – this can include changes in the amount of urine and/or abnormal back or side pain
  • Vertigo – in this condition, you feel like you or your surroundings are spinning and whirling, which can make you feel dizzy and affect your balance
  • Painful joints or muscles
  • Oedema – this is when extra water builds up in parts of your body, which could lead to swelling and other issues
  • Itching or rashes – these might be red patches on your skin

Rare side effects:

  • Coma
  • Hepatitis – this is a condition caused when there’s inflammation of the liver
  • Seizures – there are lots of types of seizures, but they might be recognised if you’ve got symptoms like temporary confusion, uncontrollable jerking of arms or legs or loss of consciousness
  • Decreased white cells in your body – this means your immunity is lower and you’re more likely to fall ill with infections
  • Stevens–Johnson syndrome – this is a rare disorder, which affects the skin and mucous membranes. You could recognise it with flu symptoms then a painful red/purple rash, which spreads and blisters. The disorder needs immediate treatment
  • Allergic reaction – this could mean you have trouble breathing, tongue/throat swelling, rash or hives. This needs immediate treatment, since it could be fatal

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Who is most likely to get side effects?

Your doctor will check your risk during an assessment – it’s important to let your doctor know if you’re taking any drugs, and this includes anything over-the-counter, including supplements and herbal remedies. You should do this because different drugs can interact with each other and cause some negative issues.

Some of the drugs can interact with Aciclovir – these include those used for:

  • HIV/AIDS – zidovudine
  • Bacterial or fungal infections – amphotericin B, foscarnet, gentamicin, kanamycin
  • Cancer – talimogene laherparepvec, cisplatin
  • Pain relief – Motrin, ibuprofen

Some people might have a higher risk of side effects – including those who are:

  • People with kidney problems – if you have kidney problems or a history of it, your body might not be able to clear the drug from your system too well. Because of this, the level of the drug increases in your body, potentially causing issues. It’s also possible that aciclovir decreases your kidney function, so you’ll also need to speak to your doctor about whether your dose needs changing
  • Pregnant women – there isn’t evidence to suggest that aciclovir is a risk to a fetus in a pregnant woman, but you should still talk to your doctor if you’re pregnant or are planning to conceive. You’ll need to carefully consider the benefits and potential risks before deciding to take aciclovir
  • Breastfeeding women – Aciclovir may affect a child being breastfed, since it can pass into breast milk. If you’re breastfeeding, you should tell your doctor and get some advice about whether you can take this medication whilst breastfeeding
  • The elderly – in the elderly, the kidneys don’t work as well as they used to, so it takes longer for a drug to be cleared from the body (similar to when you have kidney problems). Since the drug stays in the body for a longer time, this could increase the risk of side effects
  • Children – this drug hasn’t been studied in children younger than 2 years so might not be recommended
  • People with hypersensitivity – Aciclovir should not be used by people who are allergic to the drug itself or any of its ingredients, which means they’re likely to react negatively to it

Controlling your risk of side effects – since side effects could happen in anyone (though they don’t happen in everyone), the best way to lower your risk of side effects is to be completely honest with your doctor and tell them anything you think might be relevant. In general, keeping in good health is important in lowering the risk of many issues.

How can you recognise aciclovir side effects?

First steps – to start with, it’s always a good idea to take a look at the patient information leaflet, which usually comes with your medicine. You can use this to become familiar with the side effects, what they might look like and how common each one might be. Not everyone experiences side effects, but being informed is important.

Making the most of doctor visits – it’s also recommended that you keep a notebook of all your appointments with your doctor and any tests you might end up doing to check your response to aciclovir. In this notebook, you should write down at what times you’re taking aciclovir, what time you experience side effects (if any) and when they get better or worse. Trends like worsening of side effects after you take aciclovir should be discussed and reported.

Ruling out other causes – because a lot of drugs can cause some similar symptoms to aciclovir, like weakness and fatigue, your doctor will always check if you’re taking anything before they prescribe it. You might fall ill while you’re already taking aciclovir though, and illnesses can have an effect too. For example, you might have some stomach problems (food poisoning), headache (dehydration, cold, migraine), rash (infection, allergy) or fatigue (sleep deprivation, vitamin deficiency). In these cases, it’s important to keep your doctor updated at appointments, or sooner if more urgent.

What to do about aciclovir side effects

Check with a doctor before stopping treatment – if you think you’re having side effects because of aciclovir, it’s important that you don’t just stop taking the drug (unless it is a severe reaction). Even if you’re only experiencing mild symptoms, whether it’s recent or otherwise, you should let your doctor know immediately. They’ll let you know whether you should continue until you finish the prescription or if you should stop. Don’t just stop taking the drug yourself, since it might mean that your infection may not be completely treated or may become more difficult to treat.

Look out for signs of an emergency – in an emergency, like if you suffer from an overdose, you (or whoever is with you) should immediately call the emergency services. The symptoms in this case would be agitation, extreme sleepiness, loss of consciousness, seizures, and/or kidney failure.

Is the risk of side effects worth it?

Aciclovir is used to manage outbreaks of viral diseases. Aciclovir is used to treat infections caused by specific viruses, which cause cold sores around the mouth, shingles, genital herpes and chickenpox.

Aciclovir can help improve the symptoms of an outbreak of a viral infection because it helps the sores heal faster, keeps new sores from forming, and decreases pain/itching. Aciclovir can also help reduce how long you feel pain 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.

If you're worried about side effects, it's best to do some research – you should first read the patient information leaflet that comes with your medication. You could also talk to your doctor to see if they have any addition resources you could read to better inform you and put your mind at ease.

A doctor will only give you aciclovir if the benefits outweigh the risks – on the whole, you should remember that your doctor has prescribed this medication because they’ve judged that the benefit to you is greater than the risk of side effects. However, if you’re worried about taking the medication, make sure you discuss your concerns with your doctor.

Medically reviewed by:
Dr Kathryn Basford Accreditations: MB, ChB, MPH

Dr Kathryn Basford is a qualified GP who works as a GP in London, as well as with ZAVA. She graduated from the University of Manchester and completed her GP training through Whipps Cross Hospital in London.

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Last reviewed: 26 Feb 2019

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