Introduction

Antiviral medication is used to treat viral infections. This type of medication works by inhibiting the growth of viruses in the body, which leads to easing of symptoms and reducing the risk of spreading viral infections. Antiviral drugs are used to treat a range of viral infections, however, they are more effective in treating chronic viral infections such as HIV and herpes. They can be given alone or in combination with other antiviral medications to treat a viral infection.¹   

What are viruses? 

Viruses are a type of infectious pathogen that is formed of genetic material (either RNA or DNA depending on the type of virus) and protein. Unlike bacteria, which are a type of microorganism that can cause infectious diseases, viruses cannot make new virus particles on their own and require the cells of another organism, known as a host cell. 

They do this by entering the host cell and hijacking its cell machinery to replicate. Viruses don’t only infect humans and animals – they can infect plants, fungi, and even bacteria. Viruses can be spread in a variety of different ways, which include: 

• Respiratory droplets
• Oral-faecal route 
• Insect bites 
• Contaminated surfaces 
• Sexual contact²

How do antiviral medications work? 

There are many ways antiviral drugs can prevent the production and spread of viruses in the body. 

Depending on the drug type, antiviral drugs can: 

• Lower the viral load to reduce the risk of transmission 
• Inhibit viruses from entering the cell and replicating 
• Stimulate the immune system to fight off the virus

Types of antiviral medication 

Common antiviral medications include: 

• Nucleoside reverse transcriptase inhibitors (NRTIs) – used to treat HIV
• Aciclovir – used to treat herpes virus¹ 
• Direct-acting antivirals (DAA) – used to treat hepatitis C³

Aciclovir 

Aciclovir (or acyclovir) is a common antiviral drug that is used to effectively treat a range of herpes viruses, which include herpes simplex virus (HSV), varicella-zoster virus (VZV), and Epstein-Barr virus (EB), with little damage to healthy cells. The drug works by inhibiting the synthesis of viral DNA in infected cells.⁴ Notably, the World Health Organisation (WHO) has included aciclovir in the WHO Model List of Essential Medicines.  

Oseltamivir (Tamiflu)

Oseltamivir, also referred to by the brand name Tamiflu, is another antiviral drug that is used to treat influenza. The drug works by preventing the release of virus particles from the infected host cell and thus preventing the spread of the virus in the body. This results in a reduction in the severity of flu symptoms and how long the individual experiences the symptoms. 

Lamivudine 

Lamivudine is an antiretroviral drug that is used in combination with other drugs to treat HIV-1. The drug is also used to treat hepatitis B. It works by inhibiting the production of viral DNA, therefore preventing new virus particles from being synthesised. 

General side effects 

Antiviral medication can be toxic to uninfected, healthy cells and they can cause side effects in some people. Common side effects shared by many antiviral drugs include:  

Headaches 

It is currently unknown why some antiviral medications can cause headaches. Make sure you drink plenty of water as headaches may be caused by dehydration. Paracetamol can be taken with many antivirals to elevate some of the pain, however, please speak to your doctor if your medication has any drug interactions. 

Dizziness 

Dizziness can be improved by sitting or lying down. Please speak to your doctor if this is occurring regularly as they may advise you to not drive or use machinery until the dizziness is treated. 

Diarrhoea  

Diarrhoea commonly leads to dehydration, therefore drink lots of water with electrolytes to prevent this. If the diarrhoea lasts more than two days, please speak to a doctor as they can prescribe you medication to alleviate the symptom. 

Nausea and vomiting 

Avoid foods that exacerbate your nausea and try to eat bland foods. Make sure to drink plenty of water to prevent dehydration. 

These side effects are usually short-term and will only last a few days or weeks. However, some long-term antiviral medications such as the ones used to treat HIV may have additional side effects like high cholesterol, which may put you at risk of heart disease. Please speak to your doctor if you experience any of the symptoms listed above as they can guide you on ways to manage them.

Should I continue to take antiviral medication if I experience side effects?

Doctors prescribe antiviral medication despite the risk of adverse effects. Do not stop taking any antiviral medication unless your doctor tells you, particularly if you have a chronic disease such as hepatitis or HIV. Ceasing HIV medication causes your viral load to increase to detectable levels, your CD4 count will begin to drop and make you more susceptible to other infections. In some cases, ceasing HIV medication can lead to the development of drug-resistant strains, which will limit your treatment options. 

Rare side effects

Aciclovir 

Like all drugs, aciclovir can lead to a range of side effects, some more severe and rare than others. Toxicology studies have reported side effects involving the urinary system such as oliguria (low urine output) and low back pain in patients taking the drug. Although rare, aciclovir has been linked to acute renal impairment with renal function recovering completely after the withdrawal of acyclovir and additional treatments. There also have been cases of itchy skin and anaphylactic shock in those allergic to acyclovir.⁴ If you experience any allergic reactions that may be caused by aciclovir, please inform your doctor. 

Oseltamivir (Tamiflu) 

There have been severe side effects in individuals taking oseltamivir which include abnormal behaviour, delirium, and impaired perception.⁵ Please inform your doctor if you experience mood changes and abnormal behaviour that may be linked to oseltamivir. Individuals may also have an allergic reaction to oseltamivir, with symptoms such as a skin rash, difficulty breathing, and swelling of the throat or tongue. Call 999 if you experience any of these allergic symptoms as you may be going into anaphylaxis. 

Lamivudine  

Along with the common side effects of antiviral medication, there have also been cases of more severe adverse effects experienced by individuals taking Lamivudine. Pancreatitis, particularly in children, has been reported as an adverse effect. Other severe side effects include muscle pain and aplastic anaemia. 

Summary 

Antiviral medications are used to treat a range of viral infections and diseases. They can be used as a sole treatment or in combination with other antiviral drugs to treat. Like all medications, antiviral drugs come with some side effects that usually stop after the antiviral treatment is completed. However, those on long-term antivirals to treat chronic viral diseases such as HIV and hepatitis B may experience side effects for longer.⁶ Severe adverse effects from antiviral medication have been reported, however these are rare. It is important to speak to your doctor if you are experiencing any side effects. They can help you manage them or prescribe you a different type of antiviral drug. 

FAQs

Are side effects the same for all antiviral medications? 

Antiviral medications may have similar side effects, however, more severe and rare side effects are different depending on the type of antiviral drug. 

How long do antiviral side effects typically last? 

The duration of side effects can vary. Please speak to your doctor if your symptoms are impacting your day-to-day life. 

When should I report my side effects to my doctor? 

More common side effects like headaches and dizziness can be reported to your doctor so they can help you manage them with other medication. Your doctor may decide to prescribe a different type of antiviral drug that has fewer side effects. If the symptoms are life-threatening such as allergic reactions, you should call 999 so you can receive emergency care. 

Can you experience drug resistance to antiviral medication? 

Yes, there is a risk of the virus becoming resistant to the antiviral drug, particularly when treating a chronic disease. Please make sure you take the drugs as prescribed and you do not miss any doses.