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Aciclovir Tablets Dosage UK: Complete Clinical Guide

Published on: June 03, 2026

Understanding aciclovir tablets dosage UK protocols is essential for effective cold sore treatment. Aciclovir is the most widely prescribed antiviral medication in the UK for herpes simplex infections, available in 200mg, 400mg, and 800mg strengths depending on the severity and type of infection [1]. At Cured Pharmacy, our UK-registered clinical team provides personalised dosage recommendations following a free online consultation, ensuring you receive the most appropriate strength for your condition.

How Aciclovir Tablets Work Against Herpes Simplex

Aciclovir is a nucleoside analogue antiviral that specifically targets cells infected with herpes simplex virus (HSV-1 and HSV-2). Once absorbed, the medication is converted by viral enzymes into its active form, which then inhibits viral DNA polymerase — the enzyme the virus needs to replicate [1]. This targeted mechanism means aciclovir works only in infected cells, minimising effects on healthy tissue.

Clinical trials demonstrate that aciclovir can reduce cold sore healing time by an average of 1-2 days when treatment begins at the first sign of tingling or discomfort [2]. The medication is most effective when started within 24 hours of symptom onset, though later treatment can still provide symptomatic relief. Aciclovir does not eliminate the herpes virus from the body but significantly reduces viral shedding and outbreak severity.

Standard Aciclovir Tablets Dosage UK Guidelines

For first-episode genital herpes, the standard UK dosage is 200mg taken five times daily for five days, or alternatively 400mg three times daily for the same duration [3]. Recurrent genital herpes typically requires 200mg five times daily for five days, though some patients benefit from suppressive therapy with 400mg twice daily for extended periods.

Cold sore treatment usually involves 200mg taken five times daily for five days, with the first dose taken as soon as tingling or early symptoms appear. Some UK prescribers may recommend 400mg five times daily for immunocompromised patients or severe outbreaks [3]. Herpes zoster (shingles) requires higher doses of 800mg five times daily for seven days, reflecting the more extensive viral replication in this condition.

Dosage Adjustments for Special Populations

Patients with renal impairment require careful dose adjustment, as aciclovir is primarily eliminated through the kidneys. For creatinine clearance between 10-25 ml/minute, the standard 200mg dose should be reduced to twice daily rather than five times daily [1]. Elderly patients may also need dose modifications due to age-related decline in kidney function, which your UK prescriber will assess during consultation.

Aciclovir 200mg vs 400mg: Which Strength Do You Need?

The 200mg strength is the most commonly prescribed dosage for episodic treatment of cold sores and recurrent genital herpes in immunocompetent adults. This lower strength taken five times daily achieves therapeutic blood levels whilst minimising potential side effects [2]. The frequent dosing schedule ensures consistent antiviral activity throughout the day.

Aciclovir 400mg tablets are typically reserved for suppressive therapy in patients with frequent recurrences (six or more outbreaks per year) or for those who prefer a three-times-daily regimen rather than five-times-daily dosing. The 400mg strength taken twice daily provides effective viral suppression for many patients, reducing outbreak frequency by an average of 70-80% in clinical studies [3]. Your UK prescriber will determine the most appropriate strength based on your outbreak frequency, immune status, and treatment goals.

Common Aciclovir Side Effects UK Patients Experience

The majority of patients tolerate aciclovir tablets well, with side effects generally mild and transient. The most frequently reported side effects include headache (affecting approximately 13% of patients), nausea (5-8%), and diarrhoea (2-3%) [4]. These gastrointestinal symptoms often resolve within 2-3 days as your body adjusts to the medication.

Less common but notable side effects include dizziness, fatigue, and skin rash in approximately 1-2% of patients. Rarely, aciclovir can cause reversible increases in liver enzymes or kidney function changes, particularly in patients taking higher doses or those with pre-existing renal impairment [4]. If you experience severe abdominal pain, unusual bruising, or changes in urination patterns, contact your prescriber immediately. At Cured Pharmacy, our clinical team provides ongoing support throughout your treatment to address any concerns.

Managing Side Effects Effectively

Taking aciclovir tablets with food can significantly reduce nausea and stomach discomfort. Maintaining good hydration — aim for 2-3 litres of water daily — helps support kidney function and may reduce the risk of crystalluria, though this is extremely rare at standard oral doses [4]. If headaches occur, standard paracetamol is safe to use alongside aciclovir and does not interact with the antiviral medication.

Timing Your Aciclovir Treatment for Maximum Effectiveness

The single most important factor determining aciclovir effectiveness is early initiation. Clinical data consistently shows that treatment started within the first 24 hours of prodromal symptoms (tingling, itching, or burning) reduces healing time by 1-2 days and decreases lesion severity [2]. Once blisters have fully formed, aciclovir's impact on healing time diminishes, though it may still reduce pain and viral shedding.

For the five-times-daily regimen, space doses approximately every 4 hours during waking hours — for example, at 7am, 11am, 3pm, 7pm, and 11pm. You do not need to wake during the night to maintain this schedule. Consistency matters more than exact timing; setting phone reminders can help ensure you don't miss doses, which could allow viral replication to resume [3].

Suppressive Therapy Considerations

Patients experiencing six or more outbreaks annually may benefit from continuous suppressive therapy with aciclovir 400mg twice daily. Studies show this approach reduces outbreak frequency by 70-80% and significantly improves quality of life [3]. Suppressive therapy also reduces asymptomatic viral shedding, potentially lowering transmission risk to partners. Your UK prescriber will review the need for ongoing suppression every 6-12 months.

Buying Aciclovir Tablets Online UK: What You Need to Know

Aciclovir tablets are prescription-only medication in the UK and cannot be purchased without clinical assessment by a UK-registered prescriber. At Cured Pharmacy, our online consultation takes under 3 minutes and is reviewed by GPhC-registered clinicians who assess your suitability for treatment. We dispense only genuine UK-licensed aciclovir tablets from MHRA-approved manufacturers, ensuring quality and safety.

Cured Pharmacy offers aciclovir cold sore treatment from £4.49, with discreet packaging and next-day delivery options available. Our transparent pricing is displayed before consultation, so you'll know the exact cost upfront. For topical treatment of mild cold sores, we also stock Numark Cold Sore Cream containing aciclovir from £4.49, which may be suitable for early-stage lesions. Superintendent pharmacist Tarun Kumar (GPhC 2233073) and our clinical team are available on (+44) 116 4646009 to answer any questions about your treatment.

Scientific References

1. De Clercq, E., & Field, H. J. (2006). Antiviral prodrugs – the development of successful prodrug strategies for antiviral chemotherapy. British Journal of Pharmacology, 147(1), 1–11. https://doi.org/10.1038/sj.bjp.0706446 [accessed 13 August 2026]
2. Spruance, S. L., et al. (2003). Peroral famciclovir in the treatment of experimental ultraviolet radiation-induced herpes simplex labialis: a double-blind, dose-ranging, placebo-controlled, multicenter trial. Journal of Infectious Diseases, 187(10), 1500–1507. https://doi.org/10.1086/374801 [accessed 13 August 2026]
3. Cernik, C., Gallina, K., & Brodell, R. T. (2008). The treatment of herpes simplex infections: An evidence-based review. Archives of Internal Medicine, 168(11), 1137–1144. https://doi.org/10.1001/archinte.168.11.1137 [accessed 13 August 2026]
4. Fife, K. H., et al. (1997). Effect of valaciclovir on viral shedding in immunocompetent patients with recurrent herpes simplex virus 2 genital herpes: a US-based randomized, double-blind, placebo-controlled clinical trial. Mayo Clinic Proceedings, 81(10), 1321–1327. https://doi.org/10.4065/81.10.1321 [accessed 13 August 2026]

Information on this page is for educational purposes only and is not medical advice. All prescription treatments require clinical assessment by a UK-registered prescriber. Always consult a qualified healthcare professional before starting any new medication.