The safety and efficacy of clindamycin phosphate foam 1% versus clindamycin phosphate topical gel 1% for the treatment of acne vulgaris

Journal of Drugs in Dermatology, Jan-Feb, 2005 by Alan R. Shalita, Judith A. Myers, Lincoln Krochmal, Alex Yaroshinsky

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Efficacy Analyses of Clindamycin Foam and Vehicle Foam

Additional analyses were performed to demonstrate the superiority of clindamycin foam versus vehicle foam. The proportion of patients with an ISGA score of 0 or 1 at Week 12 (end of treatment) was compared in these 2 groups using the Cochran-Mantel-Haenszel (CMH) test stratified by site. Consistency of the results across investigative sites was verified by the Breslow-Day test.

The mean percent reduction from baseline to Week 12 in each of 3 lesion counts for patients in the clindamycin foam and vehicle foam groups was analyzed using the ANOVA model with terms for treatment, site, and treatment-by-site interaction. If the treatment-by-site interaction was not statistically significant at the 0.1 significance level, the ANOVA model without interaction was used to assess treatment differences. In order to establish superiority of clindamycin foam to vehicle foam, statistical significance had to be achieved for 2 of 3 lesion counts (total, inflammatory, and noninflammatory).

Safety Analyses

A safety analysis was performed on all patients who were randomized and dispensed study medication. All adverse experiences were compared based on a chi-square test (a = .10) when the incidence was at least 5% in any treatment group. Vehicle gel was excluded from statistical comparisons.

Results

Patient Characteristics

Between September 2002 and August 2003, a total of 1026 patients were randomly assigned to 4 treatments: 386 in the clindamycin foam group, 385 in the clindamycin gel group, 127 in the vehicle foam group, and 128 in the vehicle gel group. There were no statistically significant differences among the treatment groups in demographic characteristics (Table 2). At baseline, patients in the 4 treatment groups also had comparable mean total, inflammatory, and noninflammatory lesion counts, as well as similar distributions of ISGA scores (predominantly a score of 3 in all groups) at baseline (Table 2).

The disposition of the patients throughout the study is illustrated in Figure 1. The proportion of patients who did not complete treatment was similar in active and vehicle groups: 11% of patients in the clindamycin foam group versus 10% of patients in the clindamycin gel group, and 12% in each of the vehicle groups. Of the 111 patients who discontinued the study early, the most common reasons were: lost to follow-up (n = 51), patient decision (n = 42), patient noncompliance (n = 8), adverse experiences (n = 3), and disease progression (n = 1) (see Figure 1).

Efficacy Analyses Comparing Clindamycin Foam with Clindamycin Gel

ISGA Score

At the end of the 12-week treatment course, 120/386 patients (31%) in the clindamycin foam group, 105/385 patients (27%) in the clindamycin gel group, 23/127 patients (18%) in the vehicle foam group, and 26/128 patients (20%) in the vehicle gel group achieved treatment success (ie, had an ISGA score of 0 or 1) (Figure 2). The difference between clindamycin foam and clindamycin gel groups in the proportion of patients who achieved treatment success favored clindamycin foam by an estimated 4% (95% confidence interval, -2.60% to 10.23%). The lower limit of the confidence interval of -2.60% was greater than the set lower noninferiority limit of -11%, indicating that the efficacy of clindamycin foam was not inferior to that of clindamycin gel based on this primary endpoint.