Tazarotene (Page 3 of 5)

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

Tazarotene is a retinoid prodrug that is converted to its active form, the cognate carboxylic acid of tazarotene, by rapid deesterification in animals and man. Tazarotenic acid binds to all 3 members of the retinoic acid receptor (RAR) family: RARα, RARβ, and RARγ but shows relative selectivity for RARβ and RARγ and may modify gene expression. The clinical significance of these findings is unknown.

The mechanism of tazarotene action in acne vulgaris is not defined. However, the basis of tazarotene’s therapeutic effect in acne may be due to its anti-hyperproliferative, normalizing-of-differentiation and anti-inflammatory effects. Tazarotene inhibited corneocyte accumulation in rhino mouse skin and cross- linked envelope formation in cultured human keratinocytes. The clinical significance of these findings is unknown.

12.2 Pharmacodynamics

The pharmacodynamics of Tazarotene Foam are unknown.

12.3 Pharmacokinetics

Following topical application, tazarotene undergoes esterase hydrolysis to form its active metabolite, tazarotenic acid. Tazarotenic acid was highly bound to plasma proteins (greater than 99%). Tazarotene and tazarotenic acid were metabolized to sulfoxides, sulfones, and other polar metabolites which were eliminated through urinary and fecal pathways.

Systemic exposure following topical application of Tazarotene Foam 0.1% was evaluated in one trial. Patients aged 15 years and older with moderate-to-severe acne applied approximately 3.7 grams of Tazarotene Foam 0.1% (N = 13) to approximately 15% body surface area (face, upper chest, upper back, and shoulders) once daily for 22 days. On Day 22, the mean (±SD) tazarotenic acid Cmax was 0.43 (±0.19) ng/mL, the AUC024h was 6.98 (±3.56) ng∙h/mL, and the half-life was 21.7 (±15.7) hours. The median Tmax was 6 hours (range: 4.4 to 12 hours). The AUC0-24h for tazarotenic acid was approximately 50-fold higher compared with the parent compound tazarotene. The mean (±SD) half-life of tazarotene was 8.1 (±3.7) hours.

Accumulation was observed upon repeated once-daily dosing as the tazarotenic acid predose concentrations were measurable in the majority of subjects. Steady state was attained within 22 days of daily application. Once-daily dosing resulted in little to no accumulation of tazarotene as predose concentrations were mostly below the quantitation limit throughout the study.

13 NONCLINICAL TOXICOLOGY

13.1 Carcinogenesis, Mutagenesis, Impairment of Fertility

Carcinogenesis:

A long-term study of tazarotene following oral administration of 0.025, 0.050, and 0.125 mg/kg/day to rats showed no indications of increased carcinogenic risk. Based on pharmacokinetic data from a shorter-term study in rats, the highest dose of 0.125 mg/kg/day was anticipated to give systemic exposure in rats approximately 2 times the AUC in acne patients treated with 2 mg/cm2 of Tazarotene Foam 0.1% over a 15% body surface area.

A long-term topical application study of up to 0.1% tazarotene in a gel formulation in mice terminated at 88 weeks showed that dose levels of 0.05, 0.125, 0.25, and 1 mg/kg/day (reduced to 0.5 mg/kg/day for males after 41 weeks due to severe dermal irritation) revealed no apparent carcinogenic effects when compared with vehicle control animals. AUC at the highest dose in mice was 49 times the AUC in acne patients treated with 2 mg/cm2 of Tazarotene Foam 0.1% over a 15% body surface area.

In evaluation of photocarcinogenicity, median time to onset of tumors was decreased and the number of tumors increased in hairless mice following chronic topical dosing with exposure to ultraviolet radiation at tazarotene concentrations of 0.001%, 0.005%, and 0.01% in a gel formulation for up to 40 weeks.

Mutagenesis:

Tazarotene was non-mutagenic in the Ames assay and did not produce structural chromosomal aberrations in a human lymphocyte assay. Tazarotene was non-mutagenic in the CHO/HGPRT mammalian cell forward gene mutation assay and was non-clastogenic in the in vivo mouse micronucleus test.

Impairment of Fertility:

No impairment of fertility was observed in rats when male animals were treated for 70 days prior to mating and female animals were treated for 14 days prior to mating and continuing through gestation and lactation with topical doses of tazarotene gel up to 0.125 mg/kg/day. Based on data from another study, the systemic drug exposure at the 0.125 mg/kg/day dose in rats would be equivalent to 7.6 times the AUC in acne patients treated with 2 mg/cm2 of Tazarotene Foam 0.1% over a 15% body surface area.

No impairment of mating performance or fertility was observed in male rats treated for 70 days prior to mating with oral doses of up to 1 mg/kg/day tazarotene. AUC at the highest dose in rats was 23 times the AUC in acne patients treated with 2 mg/cm2 of Tazarotene Foam 0.1% over a 15% body surface area.

No effect on parameters of mating performance or fertility was observed in female rats treated for 15 days prior to mating and continuing through gestation day 7 with oral doses of tazarotene up to 2 mg/kg/day. However, there was a significant decrease in the number of estrous stages and an increase in developmental effects at that dose [see Pregnancy (8.1)]. AUC at the highest dose in rats was 42 times the AUC in acne patients treated with 2 mg/cm2 of Tazarotene Foam 0.1% over a 15% body surface area.

Reproductive capabilities of F1 animals, including F2 survival and development, were not affected by topical administration of tazarotene gel to female F0 parental rats from gestation day 16 through lactation day 20 at the maximum tolerated dose of 0.125 mg/kg/day. Based on data from another study, the AUC in rats would be equivalent to 7.6 times the AUC in acne patients treated with 2 mg/cm2 of Tazarotene Foam 0.1% over a 15% body surface area.

14 CLINICAL STUDIES

In 2 multi-center, randomized, double-blind, vehicle-controlled trials, a total of 1,485 subjects with moderate-to-severe acne vulgaris were randomized 1:1 to Tazarotene Foam or vehicle applied once daily for 12 weeks. Acne severity was evaluated using lesion counts and the 6-point Investigator’s Global Assessment (IGA) scale (see Table 2). At baseline, 80% of subjects were graded as “moderate” or Grade 3 and 20% were graded as “severe” or Grade 4 on the IGA scale. At baseline, subjects had an average of 79.8 total lesions of which the mean number of inflammatory lesions was 31.9 and the mean number of non-inflammatory lesions was 47.8. Subjects ranged in age from 12 to 45 years, with 860 (58%) subjects aged 12 to 17 years; 428 (29%) subjects aged 18 to 25 years; 143 (10%) subjects aged 26 to 35 years and 54 (4%) subjects aged 36 to 45 years. Subjects enrolled in the trials by race were white (77%), black (15%), Asian (4%), and other (4%). Hispanics comprised 18% of the population. An equal number of males (49%) and females (51%) were enrolled. Treatment success was defined as a score of “clear” (Grade 0) or “almost clear” (Grade 1) and at least 2-grade improvement from the baseline score to Week 12.

Table 2. Investigator’s Global Assessment Scale
Grade Description
0 Clear Clear skin with no inflammatory or non-inflammatory lesions.
1 Almost clear Rare non-inflammatory lesions with no more than rare papules.
2 Mild Greater than Grade 1, some non-inflammatory lesions with no more than a few inflammatory lesions (papules/pustules only, no nodular lesions).
3 Moderate Greater than Grade 2, up to many non-inflammatory lesions and may have some inflammatory lesions, but no more than one small nodular lesion.
4 Severe Greater than Grade 3, up to many non-inflammatory and inflammatory lesions, but no more than a few nodular lesions.
5 Very severe Many non-inflammatory and inflammatory lesions and more than a few nodular lesions. May have cystic lesions.

Absolute and percent reductions in lesion counts and the IGA scale after 12 weeks of treatment in these 2 trials are shown in Table 3. Each trial needed to have a statistically significant reduction in 2 out of 3 lesion counts at Week 12.

Table 3. Reductions in Lesion Counts and Improvements in Investigator’s Global Assessment at Week 12
Trial 1 Trial 2
Tazarotene Foam
N = 371
Vehicle Foam
N = 372
Tazarotene Foam
N = 373
Vehicle Foam
N = 369
Inflammatory Lesions
Mean absolute reduction from Baseline 18.0 14.0 18.0 15.0
Mean percent reduction from Baseline 58% 45% 55% 45%
Non-inflammatory Lesions
Mean absolute reduction from Baseline 28.0 17.0 26.0 18.0
Mean percent reduction from Baseline 55% 33% 57% 41%
Total Lesions
Mean absolute reduction from Baseline 46.0 31.0 43.0 33.0
Mean percent reduction from Baseline 56% 39% 56% 43%
Investigator’s Global Assessment (IGA), n (%)
Minimum 2Dgrade improvement and IGA of 0 or 1 107 (29%) 60 (16%) 103 (28%) 49 (13%)

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