Know Your Acyclovir.

How Does Acyclovir Work?

Acyclovir is an antiviral medication that targets viruses in the herpes family. It has activity against herpes simplex virus type 1 (HSV-1), herpes simplex virus type 2 (HSV-2), varicella zoster virus (chicken pox), Epstein-Barr virus (EBV), and cytomegalovirus (CMV). Because it has activity against varicella zoster virus, acyclovir is also used to treat shingles, which is a painful condition that arises in people who have previously had chicken pox (usually middle age and older). Patients with AIDS (acquired immune deficiency syndrome) as a result of HIV (human immunodeficiency virus) are particularly subject to outbreaks of various strains of herpes virus. They are often treated with acyclovir for herpetic sores in the nose, mouth, and eyes.


Acyclovir reduces pain and speeds up healing of blisters and sores associated with the viruses against which it is active. It is most commonly used to treat genital herpes and cold sores. It can also prevent outbreaks of herpes virus in patients who have had it before. While it can prevent outbreaks and slow or halt the spread of the virus within one individual, acyclcovir does not prevent the spreading of herpes virus from one person to another (see Precautions below).


In cases where a mother has an active herpes outbreak at the time of child delivery, intravenous acyclovir may be given to the neonatal patient to help prevent an outbreak in the child. Acyclovir is also given to pregnant women to prevent outbreaks at the time of delivery. These outbreaks have historically led to an unnecessarily high rate of caesarean section deliveries in an attempt to reduce transmission to infants.

What Are Common Dosages for Acyclovir?

Common dosages for acyclovir vary by route of administration and formulation. Topical ointments are typically at 5% strength. Injectable acyclovir for intravenous administration comes in three strengths: eq 50 mg base/ml; eq 500 mg base/vial; and eq 1 gram base/vial. Oral tablet and capsule formulations come in 200 mg, 400 mg, and 800 mg strengths. Liquid suspension for oral delivery is prepared as 200 mg/5ml. The buccal tablet formulation of acyclovir is available only as a 50 mg preparation.

What Are the Symptoms of Acyclovir Overdose?

Symptoms of acyclovir overdose are extreme agitation, seizures, and loss of consciousness.


What Precautions Should Be Taken with Acyclovir?

Buyers and users of acyclovir should be reminded that while it may relieve their herpes symptoms and slow or prevent outbreaks, it does not prevent transmission to another individual. Patients taking acyclovir should follow their physicians’ directions regarding prevention of the transmission of herpes to other people, especially through sexual contact.


The following medications have major reactions with acyclovir and should not be taken concomitantly (they are other antiviral medications or immunosuppressant drugs often prescribed post-transplant): Astagraf XL (tacrolimus), cidofovir, Hecoria (tacrolimus), Prograf (tacrolimus), Rapamune (sirolimus), sirolimus,  tacrolimus, tizanidine, Vistide (cidofovir), and  Zanaflex (tizanidine).


Acyclovir is eliminated primarily through the kidneys. Therefore, patients with kidney disease resulting in renal impairment should be prescribed acyclovir with caution. If acyclovir therapy must be undertaken, regular kidney panels should be obtained to monitor kidney function. Dosing may have to be adjusted to take renal impairment into consideration.


Also, because acyclovir is mostly removed through the kidneys, it is also removed during hemodialysis. Acyclovir should therefore be administered after hemodialysis or an additional dose given following a hemodialysis session.

What Are the Side Effects of Acyclovir?

While acyclovir has been deemed both safe and effective by the FDA (US Food and Drug Administration), there are some noted side effects, most of which are actually quite rare but have to be reported:


  • injection site reactions for intravenous acyclovir, such as pain, swelling, or redness

  • peeling skin or chapped lips with topical applications

  • increased thirst

  • decreased urination

  • stomach pain

  • nausea and vomiting

  • diarrhea

  • headache

  • decreased appetite

  • fatigue and abnormal weakness

  • confusion

  • convulsions or seizures

  • blood in urine or stools

  • black, tarry stools

  • chills and fever

  • sore throat

  • hallucinations

  • trembling

  • bruising easily

  • loosening of skin or blistering

  • blurred vision

  • bluish tint to skin, especially in the extremities

  • blood or oozing from mucous membranes (bowel, mouth, or nose)

  • vision changes

  • clumsiness

  • decreased consciousness

  • rapid heartbeat (tachycardia)

  • irritability

  • dizziness

  • mood changes

  • swollen lymph nodes

  • sores or ulcers on the lips or mouth

  • muscle cramps or difficulty walking

  • dry, red, or irritated eyes

  • agitation or uneasiness

  • swelling

  • jaundice (yellow skin or eyes)


Users who have an allergic reaction to acyclovir may experience hives, itching, redness, swelling, tongue swelling, difficulty breathing, or difficulty swallowing. They should consult a physician immediately if this occurs.


What Is the History of Acyclovir?

Acyclovir was isolated from nucleosides in a Caribbean sponge called Cryptotethya crypta. The nucleosides from the sponge were then synthesized in the laboratory to produce the first version of acyclovir. The original nucleosides were discovered by Howard Schaffer in conjunction with his work with researchers S. Gurwara, S. Bittner, and Robert Vince, who were studying antivirals.


When Schaffer joined Burroughs Wellcome, he teamed up with pharmacologist Gertrude B. Elion to produce the drug now known as acyclovir. Schaffer received the patent on acyclovir in 1979. Antiviral medications were coming to the forefront of research at this time, and soon after, the AIDS epidemic swept the world. Gertrude Elion won the Nobel Prize for Medicine in 1988, due in part to her work on developing acyclovir. Acyclovir was first used successfully in humans by Richard Whitley, a researcher in antiviral medicine at the University of Alabama at Birmingham.



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