Clindamycin and Tretinoin Gel

Clindamycin phosphate and tretinoin gel 1.2% / 0.025% is indicated for the topical treatment of acne vulgaris in patients 12 years or older.

5.1 Colitis

Systemic absorption of clindamycin has been demonstrated following topical use of this product. Diarrhea, bloody diarrhea, and colitis (including pseudomembranous colitis) have been reported with the use of topical clindamycin. When significant diarrhea occurs, clindamycin phosphate and tretinoin gel should be discontinued.

Severe colitis has occurred following oral or parenteral administration of clindamycin with an onset of up to several weeks following cessation of therapy. Antiperistaltic agents such as opiates and diphenoxylate with atropine may prolong and/or worsen severe colitis. Severe colitis may result in death.

Studies indicate a toxin(s) produced by clostridia is one primary cause of antibiotic-associated colitis. The colitis is usually characterized by severe persistent diarrhea and severe abdominal cramps and may be associated with the passage of blood and mucus. Stool cultures for Clostridium difficile and stool assay for C. difficile toxin may be helpful diagnostically.

5.2 Ultraviolet Light and Environmental Exposure

Exposure to sunlight, including sunlamps, should be avoided during the use of clindamycin phosphate and tretinoin gel, and patients with sunburn should be advised not to use the product until fully recovered because of heightened susceptibility to sunlight as a result of the use of tretinoin. Patients who may be required to have considerable sun exposure due to occupation and those with inherent sensitivity to the sun should exercise particular caution. Daily use of sunscreen products and protective apparel (e.g., a hat) are recommended. Weather extremes, such as wind or cold, also may be irritating to patients under treatment with clindamycin phosphate and tretinoin gel.

Clindamycin phosphate and tretinoin gel 1.2% / 0.025%, is an antibiotic and retinoid combination gel product with two active ingredients. Clindamycin phosphate, USP is a water-soluble ester of the semi-synthetic antibiotic produced by a 7(S)-chloro-substitution of the 7(R)-hydroxyl group of the parent antibiotic lincomycin.

The chemical name for clindamycin phosphate, USP is Methyl 7-chloro-6,7,8-trideoxy-6-(1-methyl-trans-4- propyl-L-2-pyrrolidinecarboxamido)-1-thio-L-threo-α-D-galacto-octopyranoside 2-(dihydrogen phosphate). The structural formula for clindamycin phosphate, USP is represented below:

Clindamycin phosphate, USP:

Molecular Formula: C18H34ClN2O8PS        Molecular Weight: 504.97

The chemical name for tretinoin, USP is 3,7-Dimethyl-9-(2,6,6-trimethyl-1-cyclohexen-1-yl)-2,4,6,8- nonatetraenoic acid (all-trans form). The structural formula for tretinoin, USP is represented below:

Tretinoin, USP:

Molecular Formula: C20H28O2       Molecular Weight: 300.44

Clindamycin phosphate and tretinoin gel 1.2% / 0.025% contains the following inactive ingredients: anhydrous citric acid, butylated hydroxytoluene, edetate disodium, hydroxyethyl cellulose, glycerin, methylparaben, polysorbate 80, propylparaben, purified water, tromethamine and xanthan gum.

12.1  MECHANISMS OF ACTION

Clindamycin

[see Microbiology (12.4)].

Tretinoin

Although the exact mode of action of tretinoin is unknown, current evidence suggests that topical tretinoin decreases cohesiveness of follicular epithelial cells with decreased microcomedo formation. Additionally, tretinoin stimulates mitotic activity and increased turnover of follicular epithelial cells causing extrusion of the comedones.

12.3  PHARMACOKINETICS

In an open-label, multiple-dose study treating 12 subjects with moderate to severe acne, the percutaneous absorption of tretinoin following 14 consecutive daily applications of approximately 4 g of clindamycin phosphate and tretinoin gel was minimal. Quantifiable tretinoin plasma concentrations ranged from 1.0 to 1.6 ng/mL, with unquantifiable plasma concentrations in 50% to 92% of subjects at any given timepoint following administration. The plasma concentrations of the key tretinoin metabolites, 13- cis -retinoic acid and 4-oxo-13-cis-retinoic acid, ranged from 1.0 to 1.4 ng/mL and from 1.6 to 6.5 ng/mL, respectively. Plasma concentrations for clindamycin generally did not exceed 3.5 ng/mL, with the exception of one subject whose plasma concentration reached 13.1 ng/mL.

12.4 Microbiology

Clindamycin binds to the 50S ribosomal subunits of susceptible bacteria and prevents elongation of peptide chains by interfering with peptidyl transfer, thereby suppressing bacterial protein synthesis. Clindamycin has been shown to have in vitro activity against Propionibacterium acnes, an organism which has been associated with acne vulgaris; however, the clinical significance of this activity against P. acnes was not examined in clinical trials with clindamycin phosphate and tretinoin gel. P acnes resistance to clindamycin has been documented. Resistance to clindamycin is often associated with resistance to erythromycin.

13.1  CARCINOGENESIS & MUTAGENESIS & IMPAIRMENT OF FERTILITY

Carcinogenicity, mutagenicity and impairment of fertility testing of clindamycin phosphate and tretinoin gel have not been performed in any species.

Clindamycin

The carcinogenicity of a 1% clindamycin phosphate gel similar to clindamycin phosphate and tretinoin gel was evaluated by daily application to mice for two years. The daily doses used in this study were approximately 13 and 72 times higher than the human dose of clindamycin phosphate from clindamycin phosphate and tretinoin gel, assuming complete absorption and based on a body surface area comparison. No significant increase in tumors was noted in the treated animals. For purposes of comparisons of the animal exposure to human exposure, the recommended human topical clinical dose is defined as 1 g of clindamycin phosphate and tretinoin gel applied daily to a 60 kg person.

Fertility (Segment 1) studies in rats treated orally with up to 300 mg/kg/day of clindamycin (approximately 290 times the amount of clindamycin delivered from the recommended clinical dose for clindamycin phosphate and tretinoin gel, based on a body surface area comparison) revealed no effects on fertility or mating ability.

Tretinoin

In two independent studies with long-term topical application of tretinoin in mice, carcinogenicity was not observed. In both studies, tretinoin was administered topically (0.025% or 0.1%) three times per week for up to two years. No carcinogenicity was observed with maximum effects of dermal amyloidosis in the basal layer of the skin.

Tretinoin has been shown to enhance photoco-carcinogenicity in properly performed specific studies, employing concurrent or intercurrent exposure to the drug and UV radiation. The contribution of clindamycin to that effect is unknown. Although the significance of these studies to humans is not clear, patients should minimize exposure to sun.

The genotoxic potential of tretinoin was evaluated in an in vitro Ames Salmonella reversion test and an in vitro chromosomal aberration assay in Chinese hamster ovary cells. Both tests were negative.

In oral Segment 1 studies in rats treated with tretinoin, the no-observed-effect-level was 2 mg/kg/day (~78 times the recommended clinical dose assuming 100% absorption and based on body surface area comparison).