Antiviral Drugs For Shingles

This article aims to provide more insight into the most common antiviral options used to treat shingles - a viral infection which predominantly affects those over the age of 50 and can have debilitating life implications if not managed appropriately.

Introduction to shingles

Varicella-zoster virus (VZV) is a virus responsible for two infectious diseases: chickenpox and shingles (also known as herpes zoster).¹ Someone’s first infection with VZV leads to the development of chickenpox. After this initial infection, the virus inactivates and rests within the nervous system. Some will be fortunate enough for the virus to remain dormant. For others, the virus may reactivate later in life, causing the infection known as shingles.² 

Shingles is a viral infection of the nerve and the skin that the nerve connects to .² Specific groups of nerves supply very specific areas of skin called dermatomes. Therefore, if the disease affects a particular nerve group, the resultant symptoms will only be evident on the patch of skin supplied by that group. In the case of shingles, this will result in a painful red, blistered rash which looks very similar to chickenpox.²

Transmission and symptoms

When it comes to the question, ‘Is shingles contagious?’, there is an important distinction to make. Shingles itself, defined by pain and its characteristic blistered rash, is not contagious. However, the virus which causes it, VZV, can be spread if someone comes into contact with the fluid in these blisters. Therefore, it is a general rule that everyone with shingles is contagious “until the last blister has dried and scabbed”.³ Contact with this fluid can cause chickenpox in those who have never had chickenpox before and/or have not been vaccinated against it.⁴

Shingles is an infection which typically affects people over the age of 50, however, it can affect anyone at any age who has already had chickenpox.⁵ You may suspect someone has shingles if they begin to experience the following symptoms:

• Pain, tingling or an itching sensation over a specific area of skin. This sensation may be constant, or happen in sudden attacks. It can also be worsened by touching the skin
• Fatigue
• Flu-like symptoms (e.g. fever, chills, headache, feeling unwell)⁶
• A red, blistered rash over the same clearly defined area of skin. This rash usually occurs a few days after the above symptoms, and usually only affects one side of the body; usually the chest or waist, but can occur anywhere.^4,5,7

If you or anyone around you begins to experience these symptoms, please seek medical attention as soon as possible to ensure the best management.

Shingles can clear up after around two to four weeks, with the painful rash fading and potentially only leaving some scarring. However, there is also a significant likelihood that people infected with shingles will develop long-term complications. The most common of these is long-lasting pain known as post-herpetic neuralgia (PHN).⁷ PHN is defined as pain associated with shingles that continues for three months after initial infection.⁷

This complication most commonly affects those aged over 60 and can have a very debilitating effect on a sufferer’s physical and mental well-being.⁷ Further complications include muscle weakness, visual changes, and a combination of one-sided facial weakness and hearing problems known as Ramsay Hunt syndrome.⁴ 

Avoiding these debilitating complications is why it is important to seek medical attention as soon as you suspect you have shingles. However, it is important to note that, even if an individual does develop post-herpetic neuralgia, treatments are available. Painkillers and antivirals have very important roles to play in controlling symptoms and reducing the severity of the infection.⁷

Of course, prevention is indeed the best cure, therefore in the UK, a shingles vaccination programme has been established. This programme administers shingles vaccinations to those at high risk of developing shingles, i.e. those aged over 50 orwith weakened immune systems.⁸ This article, however, will focus primarily on the role of antivirals suitable for those who have already acquired the infection and are experiencing symptoms. 

Importance of antiviral drugs for shingles

The main goals of using antiviral drugs to manage shingles include:

• Reducing the extent of the viral infection (by stopping the virus from replicating inside the nervous system)
• Controlling symptoms e.g., reducing pain severity, stopping new blisters from forming
• Preventing complications⁹

Due to the benefits of using antivirals, even though shingles does typically go away on its own, these drugs are considered for use in all patients, especially those at high risk of complications. This includes patients who:

• Have severe shingles
• Are aged over 50
• Have weakened immune systems (e.g. those living with HIV)⁹

The earlier this treatment is started, the better, with treatment being most effective if started within 72 hours of the onset of symptoms.¹⁰ The emphasis on treatment being started within 72 hours of symptoms onset lies in aiming to prevent the development of severe complications, such as PHN.⁷

Types of antiviral drugs for shingles

The three most common antivirals used for shingles are:

• Aciclovir
• Valacyclovir 
• Famciclovir

These are all gold-standard drugs used to stop the replication of VZV in the body, and therefore reduce pain and the formation of new blisters.¹⁰ However, each of them varies slightly in how they work in the body, and thereforetheir efficacy.

Aciclovir can be considered as the parent of valacyclovir and famciclovir. When taken, the body converts aciclovir into its active form, which interferes with VZV’s ability to replicate.¹¹ Valaciclovir however, is a modified version of aciclovir which is converted into aciclovir in the body.¹² Similarly, famciclovir is converted into an active form called penciclovir when ingested.¹³

The extra step of conversion into an active form for both valaciclovir and famciclovir allows for better absorption of the antiviral into the blood, enabling lower doses of these antivirals to produce the same effect as larger doses of aciclovir.¹⁴ 

The difference in the effectiveness of these antivirals is evident in the way they are prescribed. Under the British Medical Journal’s (BMJ) guidelines, both famciclovir and valaciclovir are suggested to be taken as oral tablets every 8 hours for 7 days. Meanwhile, in order to achieve the same therapeutic effect, aciclovir has a more intense regimen of five daily oral tablets for a period of 7-10 days.¹⁵ 

Generally, the side effects of antivirals are not severe, unless an individual experiences a serious allergic reaction (anaphylaxis). The most common side effects include headaches, diarrhoea, nausea and vomiting, dizziness, and drowsiness.¹⁶ If you do experience dizziness or drowsiness, it is advised to avoid driving, operating machinery or any other activities that could put you at risk, and to seek medical advice promptly.¹⁶

Limitations to antiviral treatments and research

Although the antiviral drugs currently in use for shingles are highly effective in reducing symptoms and reducing pain, there are still limitations. The most notable limitations of current antivirals are their time-sensitive efficacy in preventing PHN and the intensive treatment regimen.17 Furthermore, there is emerging research suggesting the existence of VZV that is resistant to treatment with aciclovir18. These limitations suggest the need for new advancements in the development of antivirals for shingles. More specifically, they suggest the need for medication which fits with patient behaviours and preferences; an intensive treatment regimen may not be suitable for patients with busy lifestyles, or those who struggle with adhering to a strict, time-sensitive treatment plan.

Summary

Varicella-zoster virus (VZV) is a virus that causes both chickenpox and shingles, the latter resulting from the reactivation of a VZV infection resting in the body’s nervous system. Shingles presents as a painful, blistering rash localised to specific nerve areas known as dermatomes. Those most at risk of developing shingles include individuals over 50 who have had chickenpox in the past and those with weakened immune systems. Although shingles itself isn't directly contagious, the virus can spread through contact with blisters, potentially causing chickenpox in vulnerable individuals.

Shingles symptoms include pain or tingling sensations, fatigue, flu-like symptoms, and a red, blistering rash. These symptoms may typically resolve in a few weeks but may lead to long-term complications like post-herpetic neuralgia (PHN); persistent pain after a shingles infection.

Antiviral drugs play a crucial role in managing shingles by limiting viral replication within the body, reducing pain, and preventing severe complications. In order to achieve the best result, it is advised that antiviral drugs such as aciclovir, valaciclovir and famciclovir should be started within 72 hours of symptom onset. Side effects of these antivirals are generally mild, including headaches, nausea, and dizziness. However, drug resistance and the time-sensitive nature of treatment are notable limitations.

In order to address these shortcomings, emerging therapies should focus on tackling VZV-resistant strains and improving the effectiveness of these drugs.