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Zovirax Injection

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Zovirax Injection

ZOVIRAX®
(acyclovir sodium) for Injection
FOR INTRAVENOUS INFUSION ONLY

DRUG DESCRIPTION

ZOVIRAX is the brand name for acyclovir, a synthetic nucleoside analog active against herpesviruses. Acyclovir sodium for injection is a sterile lyophilized powder for intravenous administration only. Each 500-mg vial contains 500 mg of acyclovir and 49 mg of sodium, and each 1,000-mg vial contains 1,000 mg acyclovir and 98 mg of sodium. Reconstitution of the 500-mg or 1,000-mg vials with 10 mL or 20 mL, respectively, of Sterile Water for Injection, USP results in a solution containing 50 mg/mL of acyclovir. The pH of the reconstituted solution is approximately 11. Further dilution in any appropriate intravenous solution must be performed before infusion (see DOSAGE AND ADMINISTRATION: Method of Preparation and Administration).

Acyclovir sodium is a white, crystalline powder with the molecular formula C8H10N5NaO3 and a molecular weight of 247.19. The maximum solubility in water at 25°C exceeds 100 mg/mL. At physiologic pH, acyclovir sodium exists as the un-ionized form with a molecular weight of 225 and a maximum solubility in water at 37°C of 2.5 mg/mL. The pka's of acyclovir are 2.27 and 9.25.

The chemical name of acyclovir sodium is 2-amino-1,9-dihydro-9-[(2-hydroxyethoxy)methyl]-6H-purin-6-one monosodium salt; it has the following structural formula:

ZOVIRAX®  (acyclovir sodium) Structural Formula Illustration

VIROLOGY

Mechanism of Antiviral Action: Acyclovir is a synthetic purine nucleoside analogue with in vitro and in vivo inhibitory activity against herpes simplex virus types 1 (HSV-1), 2 (HSV-2), and varicella-zoster virus (VZV).

The inhibitory activity of acyclovir is highly selective due to its affinity for the enzyme thymidine kinase (TK) encoded by HSV and VZV. This viral enzyme converts acyclovir into acyclovir monophosphate, a nucleotide analogue. The monophosphate is further converted into diphosphate by cellular guanylate kinase and into triphosphate by a number of cellular enzymes. In vitro, acyclovir triphosphate stops replication of herpes viral DNA. This is accomplished in 3 ways: 1) competitive inhibition of viral DNA polymerase, 2) incorporation into and termination of the growing viral DNA chain, and 3) inactivation of the viral DNA polymerase. The greater antiviral activity of acyclovir against HSV compared to VZV is due to its more efficient phosphorylation by the viral TK.

Antiviral Activities: The quantitative relationship between the in vitro susceptibility of herpes viruses to antivirals and the clinical response to therapy has not been established in humans, and virus sensitivity testing has not been standardized. Sensitivity testing results, expressed as the concentration of drug required to inhibit by 50% the growth of virus in cell culture (IC50), vary greatly depending upon a number of factors. Using plaque-reduction assays, the IC50 against herpes simplex virus isolates ranges from 0.02 to 13.5 mcg/mL for HSV-1 and from 0.01 to 9.9 mcg/mL for HSV-2. The IC50 for acyclovir against most laboratory strains and clinical isolates of VZV ranges from 0.12 to 10.8 mcg/mL. Acyclovir also demonstrates activity against the Oka vaccine strain of VZV with a mean IC50 of 1.35 mcg/mL.

Drug Resistance: Resistance of HSV and VZV to acyclovir can result from qualitative and quantitative changes in the viral TK and/or DNA polymerase. Clinical isolates of HSV and VZV with reduced susceptibility to acyclovir have been recovered from immunocompromised patients, especially with advanced HIV infection. While most of the acyclovir-resistant mutants isolated thus far from such patients have been found to be TK-deficient mutants, other mutants involving the viral TK gene (TK partial and TK altered) and DNA polymerase have been isolated. TK-negative mutants may cause severe disease in infants and immunocompromised adults. The possibility of viral resistance to acyclovir should be considered in patients who show poor clinical response during therapy.

What are the possible side effects of acyclovir injection (Zovirax)?

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Stop using acyclovir and call your doctor at once if you have a serious side effect such as:

  • urinating less than usual or not at all;
  • fever, chills, body aches, flu symptoms;
  • a red, blistering, peeling skin rash;
  • jaundice (yellowing of the skin or eyes);
  • swelling, pain, tenderness, or skin changes where the injection was given;
  • pale skin, easy bruising or...

Read All Potential Side Effects and See Pictures of Zovirax Injection »

What are the precautions when taking acyclovir for injection (Zovirax Injection)?

Before using acyclovir, tell your doctor or pharmacist if you are allergic to it; or to valacyclovir; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

Before using this medication, tell your doctor or pharmacist your medical history, especially of: kidney disease, liver disease, immune system problems.

This medication contains sodium. Consult your doctor or pharmacist if you are on a salt-restricted diet or if you have a condition that could be worsened by an increase in salt intake (e.g., congestive heart failure).

Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs,...

Read All Potential Precautions of Zovirax Injection »

Last reviewed on RxList: 9/7/2007
This monograph has been modified to include the generic and brand name in many instances.

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Zovirax Injection - User Reviews

Zovirax Injection User Reviews

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Report Problems to the Food and Drug Administration

 

You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.


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