ZOVIRAX
General description

Zovirax is the brand name used by Glaxo Wellcome Inc. for the drug acyclovir (Roxane, Mylan, and Novopharm also put out their own forms of acyclovir). Acyclovir is one of the most widely used antiviral drugs for herpesvirus infections. Glaxo distributes the drug in three forms: oral (capsule, tablet, and suspension), ointment, and as a sterile powder for intravenous adminstration.

Mechanism

Acyclovir is a synthetic purine necleoside analogue It is most effective against herpes simplex virus 1 (HSV-1), followed by herpes simplex 2 (HSV-2), and then varicella-zoster virus (VZV). Acyclovir selects specifically for enzyme thymidine kinase (TK) encoded by HSV and VZV. A series of enzymes phosphorylate the drug which allows it entry into the infected cell where it halts herpes viral DNA replication by competitively inhibiting viral DNA polymerases, incorporating itself into and terminating the viral DNA chain, nad inactivating viral DN polymerases.

Indications

Zovirax is indicated for acute treatment of herpes zoster, initial and recurrent episodes of genital herpes, and for serious cases of chickenpox. Ointment is specifically used for limited nonlife-threatening mucocutaneous HSV infections in immunocompromised patients. The ointment can be used to reduce pain and in some cases lessen viral shedding. Zovirax is indicated for intravenous use in cases of HSZ and varicella-zoster infections in immunocompromised patients and in cases of severe herpes genitalis or herpes simplex encephalitis.

Usage/Dosage

Normal dosage as a function of creatine clearance for the oral forms are given in the following table:



Normal dosage regimen	Creatine Clearance (mL/min/1.73 sq. meters)
200 mg every 4 hours	>10 0-10
400 mg every 12 hours	>10 0-10
800 mg every 4 hours	>25 10-25 0-10


Ointment should be used as follows: an amount adequte to cover all lesions should be applied every 3 hours, 6 times daily for 7 days. A rubber glove or finger cot should be used in application to prevent autoinnoculation. For intravenous use, the powder should be prepared with sterile water in a ratio of 50 mg acyclovir per mL of water. For HSV infections in immunocompromised patients, 5 mg/kg should be infused at a constant rate over 1 hour evry 8 hours for 7 days for adults. For children under 12 years of age, this rate should be reduced to 250 mg/sq. meter at a constant rate over 1 hour every 8 hours for 7 days. For severe cases of herpes genitalis, the same dosages can apply over 5 days instead. In cases of herpes encephalitis, 10 mg/kg infused at a constant rate over at leaast 1 hour every 8 hours for 10 days is appropriate for adults, and 500 mg/sq. meter at a constant rate over at least 1 hour every 8 hours for 10 days. For immunocompromised varicella zoster patients, adult patients should receive 10 mg/kg at a constant rate over 1 hour every 8 hours for 7 days while pediatric patients should receive 500 mg/sq. meter for at least one hour every 8 hours for 7 days. Administration to patients with renal dysfunction should be adjusted as follows:



Creatine Clearance (mL/min/1.73 sq. meters)	Percentage of Recommended Dose	Dosing interval (hrs)
>50	100%	8
25-50	100%	12
0-25	100%	24
0-10	50%	24

Precautions

Caution should be taken to prevent aggravated renal function. Acyclovir has not been shown to be a carcinogen, teratogen, or an fertility impairment

Contraindications

Patients who develop hypersensitivity or intolerance to any of the components of acyclovir should not take the drug.

Potential Adverse Effects

Not many drug interactions have been reported with acyclovir. The most frequent side effects of the drug are nausea, fever, headache, pain, edema, confusion and hallunations (particularly in older adults), and diarrhea.