Cyclivex is aciclovir, in 200 mg and 400 mg tablets. It treats infections caused by the herpes family of viruses — cold sores, genital herpes, shingles and chickenpox. It shortens and suppresses outbreaks; it does not clear the virus from the body, and it works best started early.
What is Cyclivex?
The South African Medicine Price Registry lists Cyclivex as Schedule 4 tablets containing aciclovir 200 mg and aciclovir 400 mg. (You will see it spelled both aciclovir and acyclovir — the same medicine.)
Aciclovir is an antiviral, not an antibiotic. It has no effect on bacterial infections.
Its mechanism is unusually elegant, and explains its safety record. Aciclovir arrives inactive. It is switched on by an enzyme, thymidine kinase, that herpes viruses make and human cells do not. Once activated, it slots into the viral DNA chain being built and stops it dead. The result is that aciclovir concentrates its action almost entirely inside infected cells, largely leaving healthy ones alone — which is why a medicine that disrupts DNA replication is nonetheless well tolerated.
Two consequences follow, and both are practical:
It only works against actively replicating virus. Herpes viruses hide dormant in nerve cells between outbreaks, making no thymidine kinase and copying no DNA. Aciclovir cannot reach them there. This is why it does not cure herpes — it suppresses and shortens outbreaks, and can prevent them while taken, but the virus stays.
Timing changes the outcome more than the dose. Started within the first day or two of symptoms — ideally at the first tingle or the first sign of a rash — it can substantially shorten an episode. Started on day four, when the virus has largely finished replicating, it does much less. If you get recurrent outbreaks, ask about keeping a supply so you can start at the first symptom rather than after a doctor’s appointment.
Why is it filed under HIV and antivirals? Because it is an antiviral medicine. Aciclovir does not treat HIV. It is, however, used frequently in people living with HIV, where herpes and shingles are more common and more severe.
What is Cyclivex commonly used for?
- Cold sores (herpes labialis) on and around the lips.
- Genital herpes, both first episodes and recurrences.
- Suppressive therapy — taken continuously to reduce the frequency of recurrent genital herpes and lower transmission risk to a partner.
- Shingles (herpes zoster), where prompt treatment reduces pain and may reduce the risk of lingering nerve pain afterwards.
- Chickenpox, in adults, adolescents and others at higher risk of complications.
- Preventing herpes outbreaks in people with weakened immunity — during chemotherapy, after transplant, or with advanced HIV.
- Herpes eye infections and severe herpes infections, usually alongside specialist care.
Things worth knowing:
Higher, more frequent dosing is normal for shingles and chickenpox than for cold sores. Aciclovir is absorbed inefficiently and clears quickly, which is why it is often taken five times a day. Missing doses matters more than with most medicines.
Genital herpes is common and manageable. It carries a stigma out of all proportion to its medical significance. Suppressive treatment reduces outbreaks substantially and lowers the chance of passing it on — worth discussing frankly with a doctor rather than managing alone.
How Cyclivex fits into this medicine category
| Group | Examples | Used for |
|---|---|---|
| Herpes antivirals | Aciclovir (Cyclivex), valaciclovir, famciclovir | Cold sores, genital herpes, shingles, chickenpox |
| Antiretrovirals | Acriptega, Hetemcit | HIV — different viruses, different medicines |
| Hepatitis antivirals | Tenofovir, entecavir, sofosbuvir | Hepatitis B and C |
| Influenza antivirals | Oseltamivir | Influenza |
| Topical antivirals | Aciclovir cream | Mild cold sores |
Valaciclovir is aciclovir with better absorption — the body converts it to aciclovir, allowing fewer daily doses. If swallowing tablets five times a day is impractical, it is worth asking about.
See the HIV and antiviral medicines hub.
What to check before using Cyclivex
Kidney function is the main consideration. Aciclovir is cleared by the kidneys and can, uncommonly, crystallise in them if someone is dehydrated or the dose is too high for their kidney function. Tell your doctor if you have kidney disease or reduced kidney function — the dose is reduced accordingly.
Also mention if you:
- Are elderly. Kidney function declines with age, and confusion and drowsiness are more likely.
- Take other medicines that affect the kidneys — anti-inflammatories, some antibiotics, ciclosporin, tacrolimus.
- Take probenecid, which raises aciclovir levels.
- Have a weakened immune system — from HIV, chemotherapy, transplant medicines or long-term steroids. Infections are more severe and treatment often differs.
- Are pregnant or breastfeeding. Aciclovir has been used extensively in pregnancy and is generally considered acceptable where needed, but confirm.
Practical points:
- Drink plenty of water throughout the course. This is the simplest and most effective way to protect the kidneys.
- Start as early as possible — at the first tingle, or within 24 to 72 hours of a shingles rash appearing.
- Take doses evenly spaced and complete the course, even once the rash starts healing.
- It can be taken with or without food.
- Do not share it, and do not use a leftover course for a different problem without advice.
- Avoid touching the sores and then your eyes. Herpes infection of the eye is serious. Wash your hands.
- Herpes is transmissible when sores are present, and sometimes without them. Treatment reduces but does not eliminate that.
Possible cautions and when to ask a pharmacist or doctor
Aciclovir is generally well tolerated. The commonest effects are nausea, vomiting, diarrhoea, abdominal pain, headache, dizziness and tiredness, usually mild.
Seek medical advice promptly for:
- Confusion, hallucinations, unusual drowsiness, agitation, tremor or unsteadiness. These are uncommon, occur mainly with reduced kidney function or in older people, and usually resolve when the dose is corrected — but they need assessment quickly.
- A marked reduction in urine output, or pain passing urine.
- A rash, hives or itching.
- Unusual bruising, bleeding, or a rash of small purple spots, particularly with a weakened immune system.
- Yellowing of the skin or eyes.
Get emergency help for swelling of the face, lips or tongue with difficulty breathing, a widespread blistering or peeling rash, or a seizure.
See a doctor promptly, not later, if:
- Shingles affects your face, particularly near an eye, or the tip of your nose. This risks the eye and needs urgent assessment.
- Shingles pain is severe, or persists after the rash heals.
- The rash is spreading widely or you feel systemically unwell.
- You have a weakened immune system and develop shingles or chickenpox.
- A first episode of genital herpes is severe, or you cannot pass urine.
- Outbreaks are frequent — suppressive treatment may be a better approach than treating each one.
- The infection is not improving after a few days on treatment.
Related medicine guides
Frequently asked questions
What is Cyclivex used for? Infections caused by herpes viruses — cold sores, genital herpes, shingles and chickenpox. It contains aciclovir.
What is Cyclivex 200 mg used for? Typically cold sores and genital herpes, including suppressive treatment. The exact schedule depends on the condition.
What is Cyclivex 400 mg used for? Commonly suppressive treatment for recurrent genital herpes, and higher-dose regimens. Shingles and chickenpox usually need higher doses again.
Does it cure herpes? No. It suppresses and shortens outbreaks and can prevent them while taken, but the virus stays dormant in nerve cells where aciclovir cannot reach it.
Is it an antibiotic? No. It is an antiviral and has no effect on bacterial infections.
Does it treat HIV? No. HIV requires antiretroviral medicines. Aciclovir is often used by people living with HIV because herpes and shingles are more common in that setting.
When should I start it? As early as possible — at the first tingle of a cold sore, or within 24 to 72 hours of a shingles rash appearing. Started late it does much less.
Why so many doses a day? Aciclovir is absorbed inefficiently and clears quickly. Valaciclovir is an alternative requiring fewer daily doses.
Do I need to drink extra water? Yes. Staying well hydrated protects the kidneys, which clear the medicine.