Mechanism of Action

Adapalene acts on retinoid receptors. Biochemical and pharmacological profile studies have demonstrated that adapalene is a modulator of cellular differentiation, keratinization, and inflammatory processes all of which represent important features in the pathology of acne vulgaris.

Mechanistically, adapalene binds to specific retinoic acid nuclear receptors but does not bind to the cytosolic receptor protein. Although the exact mode of action of adapalene is unknown, it is suggested that topical adapalene normalizes the differentiation of follicular epithelial cells resulting in decreased microcomedone formation.

Pharmacokinetics

Absorption of adapalene from DIFFERIN Gel, 0.3% through human skin is low. In a pharmacokinetics study, 16 acne patients were treated once daily for 10 days with 2 grams of DIFFERIN Gel, 0.3% applied to the face, chest and back, corresponding to approximately 2 mg/cm². Fifteen patients had quantifiable (LOQ = 0.1 ng/mL) adapalene levels resulting in a mean Cmax of 0.553 ± 0.466 ng/mL on Day 10 of treatment. The mean AUC_0-24hr was 8.37 ± 8.46 ng.h/mL as determined in 15 of the 16 patients on Day 10. The terminal apparent half-life, determined in 15 of 16 patients, ranged from 7 to 51 hours, with a mean of 17.2 ± 10.2 hours. Adapalene was rapidly cleared from plasma and was not detected 72 hours after the last application for all but one subject. Exposure of potential circulating metabolites of adapalene was not measured. Excretion of adapalene appears to be primarily by the biliary route.

In a clinical study in patients with moderate to moderately severe acne, DIFFERIN (adapalene) Gel, 0.3% or Adapalene Gel, 0.1% was applied to the face and optionally to the trunk, once daily for 12 weeks. Seventy-eight (78) patients had plasma adapalene levels evaluated at Weeks 2, 8, and 12. Of the 209 plasma samples analyzed, adapalene concentrations were below the limit of detection (LOD = 0.15 ng/mL) of the method in all samples but three. For the three samples, traces of adapalene below the limit of quantification (LOQ = 0.25 ng/mL) of the method were found. One of these samples was taken at Week 12 from a male patient treated with DIFFERIN Gel, 0.3% who treated the face and the trunk for eight weeks (thereafter, only the face was treated). The second and third samples were from the Week 2 and 12 visits of a female patient treated with Adapalene Gel, 0.1% who treated only the face for 12 weeks. In this study, the average daily usage of product was 1 g/day.

CLINICAL STUDIES:

The safety and efficacy of once daily use of DIFFERIN Gel, 0.3% for treatment of acne vulgaris were assessed in one 12 week, multi-center, controlled, clinical study, conducted in a total of 653 patients 12 to 52 years of age with acne vulgaris of mild to moderate severity. All female patients of child-bearing potential enrolled in the study were required to have a negative urine pregnancy test at the beginning of the study and were required to practice a highly effective method of contraception during the study. Female patients who were pregnant, nursing or planning to become pregnant were excluded from the study.

Patients enrolled in the study were Caucasian (72%), Hispanic (12%), African-American (10%), Asian (3%), and other (2%). An equal number of males (49.5%) and females (50.5%) enrolled. Success was defined as "Clear" or "Almost Clear" in the Investigator's Global Assessment (IGA). The success rate, mean reduction, and percent reduction in acne lesion counts from Baseline after 12 weeks of treatment are presented in the following table:

Table 1: Clinical study primary efficacy results

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