Zovirax

Action

Inhibits viral DNA polymerase, thereby inhibiting replication of viral DNA. Specific for herpes simplex types 1 (HSV-1) and 2 (HSV-2), varicellazoster virus, Epstein-Barr virus, and cytomegalovirus (CMV).

Availability

Capsules: 200 mg

Cream: 5% in 2-g tube

Injection: 50 mg/ml

Ointment: 5% in 15-g tube

Powder for injection: 500 mg/vial, 1,000 mg/vial

Suspension: 200 mg/5 ml

Tablets: 400 mg, 800 mg

Indications and dosages

➣ Acute treatment of herpes zoster (shingles)

Adults: 800 mg P.O. q 4 hours while awake (five times/day) for 7 to 10 days

➣ Initial episode of genital herpes

Adults: 200 mg P.O. q 4 hours while awake (1,000 mg/day) for 10 days

➣ Chronic suppressive therapy for recurrent genital herpes episodes

Adults: 400 mg P.O. b.i.d., or 200 mg P.O. three to five times daily for up to 12 months

➣ Intermittent therapy for recurrent genital herpes episodes

Adults: 200 mg P.O. q 4 hours while awake (five times/day) for 5 days, initiated at first sign or symptom of recurrence

➣ Management of initial episodes of genital herpes and limited, non-life-threatening mucocutaneous herpes simplex virus infections in immunocompromised patients

Adults: Apply approximately ½″ ribbon of ointment per 4 square inches of surface area to sufficiently cover all lesions q 3 hours, six times daily for 7 days.

➣ Treatment of recurrent herpes labialis (cold sores)

Adults and adolescents ages 12 and older: Apply cream to infected area five times daily for 4 days.

➣ Varicella (chickenpox)

Adults and children weighing more than 40 kg (88 lb): 800 mg P.O. q.i.d. for 5 days

Children older than age 2: 20 mg/kg P.O. q.i.d. for 5 days

➣ Mucosal and cutaneous HSV-1 and HSV-2 in immunocompromised patients

Adults and children older than age 12: 5 mg/kg I.V. infusion over 1 hour given q 8 hours for 7 days

Children younger than age 12: 10 mg/kg I.V. infusion over 1 hour given q 8 hours for 7 days

➣ Herpes simplex encephalitis

Adults and children older than age 12: 10 mg/kg I.V. over 1 hour given q 8 hours for 10 days

Children ages 3 months to 12 years: 20 mg/kg I.V. over 1 hour given q 8 hours for 10 days

Children from birth to 3 months: 10 mg/kg I.V. over 1 hour given q 8 hours for 10 days

➣ Varicella zoster infections in immunocompromised patients

Adults and adolescents older than age 12: 10 mg/kg I.V. over 1 hour given q 8 hours for 7 days

Children younger than age 12: 20 mg/kg I.V. over 1 hour given q 8 hours for 7 days

Dosage adjustment

• Renal impairment

• Obesity (adult dosage based on ideal weight)

• Elderly patients

Off-label uses

• Herpes zoster encephalitis

• CMV and HSV infection after bone marrow or kidney transplantation

• Infectious mononucleosis

• Varicella pneumonia

Contraindications

• Hypersensitivity to drug or valacyclovir

Precautions

Use cautiously in:

• preexisting serious neurologic, hepatic, pulmonary, or fluid or electrolyte abnormalities

• renal impairment

• obesity

• pregnant or breastfeeding patients.

Administration

• Make sure patient is adequately hydrated before starting therapy.

• Give single I.V. dose by infusion over at least 1 hour to minimize renal damage.

• Don't give by I.V. bolus or by I.M. or subcutaneous route.

• Be aware that absorption of topical acyclovir is minimal.

Adverse reactions

CNS: aggressive behavior, dizziness, malaise, weakness, paresthesia, headache; with I.V. use-encephalopathic changes (lethargy, tremors, obtundation, confusion, hallucinations, agitation, seizures, coma)

CV: peripheral edema

EENT: vision abnormalities

GI: nausea, vomiting, diarrhea

GU: proteinuria, hematuria, crystalluria, vaginitis, candidiasis, changes in menses, vulvitis, oliguria, renal pain, renal failure, glomerulonephritis Hematologic: anemia, lymphadenopathy, thrombocytopenia, thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (in immunocompromised patients), disseminated intravascular coagulation, hemolysis, leukopenia, leukoclastic vasculitis

Hepatic: jaundice, hepatitis

Musculoskeletal: myalgia

Skin: photosensitivity rash, pruritus, angioedema, alopecia, urticaria, severe local inflammatory reactions (with I.V. extravasation), toxic epidermal necrolysis, erythema multiforme

Other: gingival hyperplasia, fever, excessive thirst, pain at injection site, anaphylaxis, Stevens-Johnson syndrome

Interactions

Drug-drug. Interferon: additive effect

Nephrotoxic drugs: increased risk of nephrotoxicity

Probenecid: increased acyclovir blood level

Zidovudine: increased CNS effects, especially drowsiness

Drug-diagnostic tests. Alanine aminotransferase, aspartate aminotransferase, bilirubin, blood urea nitrogen: increased levels

Patient monitoring

• Monitor fluid intake and output.

• Assess for signs and symptoms of encephalopathy.

• Evaluate patient frequently for adverse reactions, especially bleeding tendency.

• Monitor CBC with white cell differential and kidney function test results.

Patient teaching

• Instruct patient to keep taking drug exactly as prescribed, even after symptoms improve.

• Advise patient to drink enough fluids to ensure adequate urinary output.

• Tell patient to monitor urine output and report significant changes.

☞ Instruct patient to immediately report unusual bleeding or bruising.

• Caution patient to avoid driving and other hazardous activities until he knows how drug affects concentration and alertness.

• Advise patient to minimize GI upset by eating small, frequent servings of food and drinking plenty of fluids.

• Tell patient to use soft toothbrush and electric razor to avoid injury to gums and skin.

• Advise patient to avoid sexual intercourse when visible herpes lesions are present.

• Inform patient that he may need to undergo regular blood testing during therapy.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs and tests mentioned above.