Acyclovir (Zovirax)

  • Generic Name (USAN): Acyclovir
  • International Nonproprietary Name (INN): Aciclovir
  • Trade Name: Zovirax
  • Pregnancy Category: B (No proven risk in humans)
  • Availability: Prescription only

Acyclovir (Zovirax) is the oldest and still the most widely prescribed antiviral medication in the world. It has been available since 1985 in pill form.

Acyclovir stops the growth of Herpes simplex virus (HSV-1, HSV-2), Varicella zoster virus (the cause of chickenpox and shingles), and Epstein Barr Virus (the cause of glandular fever). It has also moderate antiviral activity against Cytomegalovirus.

Acyclovir Pros

  • Highly effective against both Herpes Simplex Viruses HSV-1 and HSV-2.
  • Save: not need to worry about serious side effects or drug interactions.
  • Widely available and inexpensive.

Acyclovir Cons

  • The main disadvantage is a frequent (4-5 times per day) dosage schedule.
  • Prescription requirement (in most countries) may delay the purchase of acyclovir (Zovirax) and the prompt treatment.
  • Starting acyclovir later than three days after symptoms appear depletes the effectiveness.
  • Acyclovir should be used with caution in people with kidney disease. The dose needs to be reduced to prevent accumulation of acyclovir and to decrease the risk of kidney damage. Drink plenty of fluids to keep your kidneys working properly.

Acyclovir for genital herpes

While genital herpes is not a life-threatening disease, once the virus has infected the body, it establishes a lifelong condition that can recur at various times with or without visible signs of a herpes outbreak.

Acyclovir does not cure herpes, but offers substantial symptoms relief and significantly reduces the duration of herpes episode.

Acyclovir is indicated for the treatment of initial and recurrent episodes of genital herpes. It may be used as chronic suppressive therapy for recurrent outbreaks. Persons who have six or more outbreaks per year or those who feel psychologically distressed by their condition are good candidates for suppressive therapy.

Acyclovir reduces the frequency of recurrences by up to 80%. And about 25-30% of people will have no further outbreaks while taking suppressive acyclovir.

Suppressive therapy does not completely prevent but significantly reduces the risk of transmission of genital herpes. Latex condoms are additional measure to prevent the spreading of HSV during sexual intercourse.

Acyclovir should be started as soon as possible after the first appearance of symptoms, such as burning, itching, and tingling, before the sores or blisters have developed. It works best during the active viral replication - the prodromal phase, which directly precedes appearance of vesicles. The antiviral may have little effect if started after onset of lesions.

Acyclovir for cold sores

Topical acyclovir 5% cream (Zovirax) slightly reduces pain, healing time, and duration of hard crust in acute cold sores (herpes labialis) attack. As a prophylaxis, oral acyclovir is generally used in cases of more than 2 episodes of cold sores in 4 months, and for recurrences that affect job performance or can lead to other health complications.

Zovirax is also FDA approved for the treatment of herpes zoster (shingles) and Varicella-zoster (chickenpox). Unlike chickenpox, herpes zoster is an occasional disease with an incidence of 10-20%.


  • 1. Goldberg LH, Kaufman R, Kurtz TO, Conant MA, Eron LJ, Batenhorst RL, Boone GS. Long-term suppression of recurrent genital herpes with acyclovir. A 5-year benchmark. Arch Dermatol. 1993 May;129(5):582-7

Last Updated: January, 2012