Zonalon

Zonalon ® Cream is indicated for the short-term (up to 8 days) management of moderate pruritus in adult patients with atopic dermatitis or lichen simplex chronicus. (See DOSAGE AND ADMINISTRATION .)

Because doxepin HCl has an anticholinergic effect and because significant plasma levels of doxepin are detectable after topical Zonalon ® Cream application, the use of Zonalon ® Cream is contraindicated in patients with untreated narrow angle glaucoma or a tendency to urinary retention. Zonalon ® Cream is contraindicated in individuals who have shown previous sensitivity to any of its components.

Drowsiness occurs in over 20% of patients treated with Zonalon ® Cream, especially in patients receiving treatment to greater than 10% of their body surface area. Patients should be warned about the possibility of sedation and cautioned against driving a motor vehicle or operating hazardous machinery while being treated with Zonalon ® Cream. The sedating effects of alcoholic beverages, antihistamines, and other CNS depressants may be potentiated when Zonalon ® Cream is used.

If excessive drowsiness occurs it may be necessary to reduce the frequency of applications, the amount of cream applied, and/or the percentage of body surface area treated, or discontinue the drug. However, the efficacy with reduced frequency of applications has not been established. Keep this product away from the eyes.

Drug Interactions Studies have not been performed examining drug interactions with Zonalon ® Cream. However, since plasma levels of doxepin following topical application of Zonalon ® Cream can reach levels obtained with oral doxepin HCl therapy, the following drug interactions are possible following topical Zonalon ® Cream application: Drugs Metabolized by P450 2D6 The biochemical activity of the drug metabolizing isozyme cytochrome P450 2D6 (debrisoquin hydroxylase) is reduced in a subset of the Caucasian population (about 7-10% of Caucasians are so-called "poor metabolizers"); reliable estimates of the prevalence of reduced P450 2D6 isozyme activity among Asian, African and other populations are not yet available.

Poor metabolizers have higher than expected plasma concentrations of tricyclic antidepressants (TCAs) when given usual doses. Depending on the fraction of drug metabolized by P450 2D6, the increase in plasma concentration may be small, or quite large (8-fold increase in plasma AUC of the TCA). In addition, certain drugs inhibit the activity of this isozyme and make normal metabolizers resemble poor metabolizers. An individual who is stable on a given dosage regimen of a TCA may become abruptly toxic when given one of these inhibiting drugs as concomitant therapy.