ACYCLOVIR 5% OINTMENT (Generic Zovirax)

Uses Dosage and Administration Cautions Drug Interactions Pharmacokinetics

Uses

Acyclovir is used topically as a 5% cream for the treatment of recurrent herpes labialis (perioral herpes, cold sores, fever blisters) in immunocompetent individuals. Acyclovir is used topically as a 5% ointment in the treatment of limited, non-life-threatening, mucocutaneous herpes simplex virus (HSV-1 and HSV-2) infections in immunocompromised individuals. The manufacturer states that acyclovir ointment may be used topically for the management of initial genital herpes; however, topical therapy is not usually recommended for the treatment of genital herpes.(See Uses: Genital Herpes.)There is no evidence that topical acyclovir will either prevent transmission of HSV infections to other individuals or prevent recurrent HSV infections when applied in the absence of signs and symptoms of infection. Acyclovir should not be used topically for prevention of recurrent HSV infections.

For systemic uses of acyclovir,

Herpes Labialis

Acyclovir 5% cream is used topically for the treatment of recurrent herpes labialis (perioral herpes, cold sores, fever blisters) in immunocompetent adults and children 12 years of age or older. Efficacy of acyclovir 5% cream in immunocompromised individuals has not been established. In 2 randomized, double-blind, vehicle-controlled studies in immunocompetent adults with a history of recurrent herpes labialis (at least 3 episodes during the past year), self initiation of topical acyclovir 5% cream within 1 hour of onset of prodromal symptoms or the first clinical sign of herpes labialis decreased the duration of the episode and also decreased patient-assessed duration of pain. In these studies, the mean duration of herpes labialis episodes for patients with a known duration was 4.3-4.6 days in those treated with topical acyclovir versus 4.8-5.2 days in those treated with vehicle cream; the mean patient-assessed duration of pain was 2.9-3.1 days and 3.2-3.5 days, respectively. There was no evidence that use of topical acyclovir prevented the development of classic herpes labialis lesions (progression to vesicles, ulcers, and/or crusts).

In immunocompromised adults with herpes labialis (oral and perioral herpes), topical application of acyclovir 5% ointment to the lesions has decreased the duration of viral shedding and the duration of pain. In one study, acyclovir was not effective in reducing total healing time or delaying the onset of recurrent infections. However, in this study, the duration of viral shedding (time from patient enrollment in the study until 2 consecutive negative cultures were obtained) was 2.5 days in acyclovir-treated patients compared with 9.5 days in placebo-treated patients; pain persisted for more than 3 weeks after onset of illness in 10% of acyclovir-treated patients and in about 50% of placebo-treated patients.

Genital Herpes

Acyclovir 5% ointment has been used in the treatment of initial episodes of genital herpes in adults. However, topical antiviral agents are not recommended for the treatment of genital herpes since these agents offer only minimal clinical benefit. The US Centers for Disease Control and Prevention (CDC) and some clinicians recommend that oral acyclovir, oral famciclovir, or oral valacyclovir be used for the treatment of first episodes of genital herpes, episodic treatment of recurrent infections, or suppressive therapy of recurrent infections in immunocompetent adults and adolescents.

Controlled studies of first episodes of genital herpes infections, both primary and non-primary, have shown that topical therapy with acyclovir 5% ointment does not reduce the frequency or delay the time of appearance of new lesions following initiation of treatment, nor does it delay the onset of recurrent infections. However, topical therapy with acyclovir generally decreases the duration of viral shedding (time from onset of therapy until the last positive culture), the duration of pain and itching, and the time required for crusting and healing of lesions in these patients.

Studies of treatment of recurrent genital herpes infections have generally shown little if any therapeutic benefit following topical therapy with acyclovir 5% ointment. In controlled studies in patients (males and females) with recurrent infections, topical acyclovir appeared to decrease the duration of viral shedding and modestly reduce the time required for crusting and healing of lesions in males. No significant effect on healing or crusting of lesions was noted in females. No significant reduction in duration or degree of pain or itching was noted in patients of either sex. Acyclovir has not been effective in reducing the frequency or delaying the onset of subsequent recurrent infections. Similar disappointing results have occurred when topical acyclovir therapy for the prevention of recurrent genital herpes infections was initiated immediately following the development of prodromal symptoms (e.g., itching, burning, tingling, numbness). In one large, placebo-controlled, multicenter study, the duration of viral shedding was reduced in females, but not males, and the time required for crusting was reduced in males, but not females; however, these reductions were of borderline significance only and there was no evidence of symptomatic improvement with acyclovir nor other differences compared with placebo.

For information on current recommendations for the treatment of genital herpes, see Uses: Genital Herpes, in Acyclovir 8:18.32.

Mucocutaneous Herpes Simplex Virus (HSV) Infections

Acyclovir 5% ointment is used topically in the treatment of limited, non-life-threatening, nongenital, mucocutaneous HSV-1 and HSV-2 infections in immunocompromised adults. However, systemic therapy (e.g., oral or IV acyclovir) generally is preferred for the treatment of mucocutaneous herpes simplex infections in immunocompromised individuals.

Ophthalmic HSV Infections

An ophthalmic ointment containing acyclovir 3% (not currently available) has been used in the topical treatment of HSV ophthalmic infections; however, commercially available acyclovir 5% ointment should not be applied to the eye.

For other uses of acyclovir, see 8:18.32.

Dosage and Administration

Administration

Acyclovir 5% cream is applied topically to affected areas of the lips and surrounding skin. The cream should not be applied to the eye, inside the mouth or nose, or to mucous membranes.

Acyclovir 5% ointment is applied topically to the skin. The ointment should not be applied to the eye. A finger cot or rubber glove should be used when applying the ointment to prevent autoinoculation of other sites and transmission of the virus to other individuals.

Dosage

Herpes Labialis

For the treatment of recurrent herpes labialis (perioral herpes, cold sores, fever blisters) in adults and children 12 years of age or older, therapy with acyclovir cream should be initiated at the earliest sign or symptoms of herpes labialis (i.e., during the prodrome or when lesions appear). The cream should be applied in sufficient quantity to cover all lesions or symptomatic areas (e.g., area with tingling). The cream should be rubbed gently into the affected area 5 times daily for 4 days. The affected area should not be covered with a dressing unless directed by a clinician.

Genital Herpes and Mucocutaneous Herpes Simplex Virus (HSV) Infections

For the treatment of initial episodes of genital herpes in adults or mucocutaneous herpes simplex infections in immunocompromised adults, therapy with acyclovir ointment should be initiated as soon as possible following the onset of signs and symptoms of infection. The ointment should be applied in sufficient quantity to adequately cover all lesions. The usual dose of acyclovir 5% ointment varies according to the total lesion area but should be approximately a 1.25-cm (0.5-inch) ribbon of ointment per 2.5-cm (4-inch) surface area. The manufacturer recommends that the ointment be gently rubbed into the affected area every 3 hours 6 times daily for 7 days. Patients should be instructed to contact their physician if no improvement occurs following 7 days of therapy. The affected area should be kept clean and dry; patients should be instructed to wear loose-fitting clothing to avoid irritation of the lesions. The manufacturer states that the recommended dose, frequency of application, and duration of treatment should not be exceeded.

Cautions

Adverse Effects

Topical acyclovir generally is well tolerated. Based on clinical experience, spontaneously reported adverse effects associated with the use of topical acyclovir are rare.

In clinical studies evaluating acyclovir 5% ointment, mild pain (including transient burning and stinging) occurred in about 30% of patients in both the active and placebo arms and treatment was discontinued in 2 of these patients. Local pruritus occurred in 4% of patients. Edema and/or pain at the application site and rash also have been reported. In several placebo-controlled studies, the frequency and type of these adverse effects were similar for acyclovir- and placebo-treated patients; therefore, these effects probably resulted from contact with or manipulation of the characteristically tender genital lesions.

In clinical studies evaluating acyclovir 5% cream, dry or cracked lips, desquamation, dry or flaking skin, burning or stinging skin, and pruritus were the most frequently reported adverse effects.

The manufacturer states that adverse systemic effects following overdosage with topically applied acyclovir 5% cream or ointment are unlikely since the drug undergoes minimal percutaneous absorption.

Precautions and Contraindications

The development of viral mutants with decreased in vitro susceptibility to acyclovir has occurred following in vitro exposure of HSV isolates to the drug and also has been observed in a small number of immunocompromised patients after repeated systemic therapy with the drug; however, the clinical importance of this decreased in vitro susceptibility is not known since the presence of these viruses did not appear to be associated with a worsening of clinical illness and, in some instances, the virus disappeared spontaneously. Although clinically important resistance has not been associated with the use of topical acyclovir, the possibility that indiscriminate use of the drug may result in such resistance should be considered.

Patients should be instructed to avoid close contact with individuals experiencing signs or symptoms of herpes simplex (HSV) infections. There is no evidence that topically applied acyclovir will prevent transmission of HSV infections to other individuals. Acyclovir 5% ointment should not be used for the prevention of recurrent HSV infections; data indicating that the ointment prevents recurrent HSV infection is not available.

The recommended dose, frequency of application, and length of treatment with topical acyclovir should not be exceeded. (See Dosage and Administration: Dosage.) Commercially available acyclovir 5% cream or ointment should not be applied to the eye.

The manufacturer states that acyclovir 5% cream has the potential for irritation and contact sensitization; contact dermatitis has been reported rarely during postmarketing surveillance.

Topical acyclovir is contraindicated in patients hypersensitive to acyclovir, valacyclovir, or any ingredient in the formulation.

Pediatric Precautions

Safety and efficacy of acyclovir 5% cream have not been established in children younger than 12 years of age. When the topical cream was used for the treatment of recurrent herpes labialis (perioral herpes, cold sores, fever blisters) in children 12-17 years of age, the safety profile was similar to that reported in adults.

Safety and efficacy of acyclovir 5% ointment have not been established in children.

Geriatric Precautions

Clinical studies using topical acyclovir 5% cream or ointment did not include sufficient numbers of patients 65 years of age and older to determine whether geriatric patients respond differently from younger patients. Other reported clinical experience has not identified differences in responses between geriatric and younger patients.

Mutagenicity and Carcinogenicity

Mutagenic changes and chromosomal damage have occurred in vitro in human lymphocytes and mouse lymphoma cells at acyclovir concentrations at least 1000 times greater than the plasma drug concentrations achievable following topical application of the ointment in humans.

In vitro cell transformation assays have shown conflicting evidence regarding the oncogenic potential of acyclovir. However, the manufacturer states that in more definitive, long-term studies of the carcinogenic potential of acyclovir in mice and rats, no difference in the frequency of benign and malignant tumors was seen when drug-treated animals were compared with control animals; in addition, acyclovir did not appear to shorten the latency of tumors.

Because systemic absorption appears to be minimal following topical application of acyclovir, dermal carcinogenicity studies have not been conducted.

Pregnancy and Lactation

Pregnancy

Acyclovir has not been shown to be teratogenic in standard tests following subcutaneous administration in rats and rabbits, IV administration in rabbits, and oral administration in mice. However, in nonstandard tests in rats, fetal abnormalities, principally involving the head and tail, were observed at higher subcutaneous acyclovir dosages, which also were associated with maternal toxicity. The drug crosses the placenta in humans following oral or IV administration. There are no adequate and controlled studies to date using acyclovir in pregnant women, and the drug should be used during pregnancy only when the potential benefits justify the possible risks to the fetus.

Lactation

Although it is not known whether acyclovir is distributed into milk following topical application, the drug is distributed into milk following oral or IV administration. Following oral administration of acyclovir in 2 nursing women, milk acyclovir concentrations were 0.6-4.1 times the simultaneous maternal plasma drug concentrations. Therefore, acyclovir ointment and cream should be used with caution in nursing women. Women who have active herpetic lesions near or on the breast should avoid nursing.

Drug Interactions

Because systemic absorption appears to be minimal following topical application of acyclovir (see Pharmacokinetics: Absorption), drug interactions between topical acyclovir and systemically administered drugs is unlikely. The manufacturer states that drug interactions in patients receiving topical acyclovir concurrently with other topical or systemic drugs have not been reported to date.

Pharmacokinetics

Absorption

Percutaneous absorption of acyclovir appears to be minimal following topical application of the drug to intact skin.

In a pharmacokinetic study in healthy adult males that evaluated topical application of acyclovir 5% cream 5 times daily for 4 days to intact skin (area of application 710 cm), plasma acyclovir concentrations obtained 1 hour after the last dose were undetectable or just above the limits of detection.

In one study in immunocompromised adults, the drug was not detected in blood or urine following topical application of acyclovir 5% ointment to intact skin (25 mg of acyclovir per application) 4 times daily for 7 days. In another study in several patients with localized varicella-zoster, plasma acyclovir concentrations were 0.28 mcg/mL or less in patients with normal renal function and 0.78 mcg/mL or less in one patient with impaired renal function.

Distribution

The distribution of acyclovir following topical application has not been determined. In vitro, acyclovir appears to be preferentially distributed into cells that are infected with herpesviruses.

Acyclovir crosses the placenta following oral or IV administration.

It is not known if the drug or its metabolites are distributed into milk following topical application. However, limited data indicate that acyclovir is distributed into milk following oral administration, generally in concentrations greater than concurrent maternal plasma concentrations.

Elimination

In vitro, acyclovir is metabolized in cells infected with herpesviruses, principally by intracellular phosphorylation of the drug by virus-coded thymidine kinase and several cellular enzymes. (See Mechanism of Action.) The metabolic fate of percutaneously absorbed acyclovir has not been fully determined.

Following systemic absorption, acyclovir is excreted principally in urine. When acyclovir 5% ointment was applied topically to the intact skin of healthy adult males (5 times daily for 4 days), approximately 0.04% of the total daily dose was detected in urine. When acyclovir 5% ointment was applied topically in immunocompromised adults with localized varicella-zoster, up to 9.4% of the total daily dose of acyclovir was excreted in urine as unchanged drug within 24 hours.

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