Aciclovir

What it is

Aciclovir is an antiviral drug active against herpes viruses. It is converted to its active form mainly inside infected cells and then blocks the viral DNA polymerase, so the virus cannot copy its genetic material. It is used for viral infections such as cold sores, genital herpes, chickenpox and shingles.

A usual adult range, not a national label — the dose and the timing differ by country and by product.

Used for

• Viral infection

Approved uses differ by country — some of these may be off-label or unapproved where you live.

What to know while taking it

It can be taken with or without food. Drinking enough fluid through the day matters, because aciclovir is cleared by the kidneys and can crystallise in the renal tubules when a person is dehydrated. Existing kidney disease calls for caution and usually for a different dosing plan set by a doctor, and creatinine and eGFR are the values used to follow kidney function during treatment. Treatment works best when started as soon as the first tingling or rash appears.

When to see a doctor

Passing much less urine than usual, swelling of the legs or face, or new flank pain suggest a kidney problem and should be seen by a doctor. Confusion, hallucinations, tremor, or a rash that spreads or blisters also warrant medical assessment.

Worth knowing

• Drink enough water
• Caution with kidney disease

Markers to watch

• Creatinine
• eGFR