Source: FDA, National Drug Code (US) Revision Year: 2022
Mechanism of action of clindamycin in acne vulgaris is unknown [see Microbiology (12.4)].
Pharmacodynamics of clindamycin phosphate foam is unknown.
In an open label, parallel group study in 24 subjects with acne vulgaris, 12 subjects (3 male and 9 female) applied 4 grams of clindamycin phosphate foam once-daily for five days, and 12 subjects (7 male and 5 female) applied 4 grams of a clindamycin gel, 1%, once daily for five days. On Day 5, the mean Cmax and AUC(0-12) were 23% and 9% lower, respectively, for clindamycin phosphate foam than for the clindamycin gel, 1%.
Following multiple applications of clindamycin phosphate foam, less than 0.024% of the total dose was excreted unchanged in the urine over 12 hours on Day 5.
No microbiology studies were conducted in the clinical trials with this product.
Clindamycin binds to the 50S ribosomal subunits of susceptible bacteria and prevents elongation of peptide chains by interfering with peptidyl transfer, thereby suppressing protein synthesis. Clindamycin has been shown to have in vitro activity against Propionibacterium acnes (P. acnes), an organism that has been associated with acne vulgaris; however, the clinical significance of this activity against P. acnes was not examined in clinical studies with clindamycin phosphate foam. P. acnes resistance to clindamycin has been documented.
The treatment of acne with antimicrobials is associated with the development of antimicrobial resistance in P. acnes as well as other bacteria (e.g. Staphylococcus aureus, Streptococcus pyogenes). The use of clindamycin may result in developing inducible resistance in these organisms. This resistance is not detected by routine susceptibility testing.
Resistance to clindamycin is often associated with resistance to erythromycin.
The carcinogenicity of a 1.2% clindamycin phosphate gel similar to clindamycin phosphate foam was evaluated by daily topical administration to mice for two years. The topical doses used in this study were approximately 3 and 15 times higher than the MRHD of clindamycin phosphate from clindamycin phosphate foam, based on BSA comparison and assuming 100% absorption. No significant increase in tumors was noted in the treated animals.
The genotoxic potential of clindamycin was evaluated in an in vitro Ames assay and in an in vivo rat micronucleus test. Both tests were negative.
Reproduction studies in rats using oral doses of clindamycin hydrochloride and clindamycin palmitate hydrochloride have revealed no evidence of impaired fertility.
In one multicenter, randomized, double-blind, vehicle-controlled clinical trial, subjects with mild to moderate acne vulgaris used clindamycin phosphate foam or the vehicle foam once daily for twelve weeks. Treatment response, defined as the proportion of subjects clear or almost clear, based on the Investigator Static Global Assessment (ISGA), and the mean percent reductions in lesion counts at the end of treatment in this study are shown in Table 2.
Table 2. Efficacy Results at Week 12:
| Efficacy Parameters | Clindamycin Phosphate Foam N=386 | Vehicle Foam N=127 |
|---|---|---|
| Treatment response (ISGA) | 31% | 18%* |
| Percent reduction in lesion counts | ||
| Inflammatory Lesions | 49% | 35%* |
| Noninflammatory Lesions | 38% | 27%* |
| Total Lesions | 43% | 31%* |
* P<0.05
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