Topicort (Desoximetasone Topical) - Description and Clinical Pharmacology

DESCRIPTION

Topicort^® (desoximetasone) Topical Spray, 0.25% contains desoximetasone as the active ingredient.

Desoximetasone is a corticosteroid with the chemical name of pregna-1, 4-diene-3, 20-dione, 9-fluoro-11, 21-dihydroxy-16-methyl-, (11β,16α)-.

Desoximetasone has the molecular formula of C₂₂H₂₉FO₄ and a molecular weight of 376.47. The CAS Registry Number is 382-67-2.

The structural formula is:

Each gram of Topicort^® Topical Spray contains 2.5 mg of desoximetasone in a clear, colorless liquid with the following inactive ingredients: glyceryl oleate, isopropyl alcohol (23.4%), isopropyl myristate, L-menthol, and mineral oil. Topicort^® Topical Spray is co-packaged with a manual spray pump for installation by the pharmacist prior to dispensing to patients.

CLINICAL PHARMACOLOGY

Mechanism of Action

Corticosteroids play a role in cellular signaling, immune function, inflammation and protein regulation; however, the precise mechanism of action in psoriasis is unknown.

Pharmacodynamics

Vasoconstrictor studies performed with Topicort^® Topical Spray in healthy subjects indicate that it is in the high to super-high range of potency as compared with other topical corticosteroids.

The potential for hypothalamic-pituitary-adrenal (HPA) axis suppression was evaluated in a study of 24 adult subjects with moderate to severe plaque psoriasis. Topicort^® Topical Spray was applied twice a day for 28 days. Twenty-one subjects had evaluable serum cortisol levels. The proportion of subjects demonstrating HPA axis suppression was 8.3% (1 out of 12) in subjects having psoriasis involvement of 10-15% of body surface area (BSA), and 22.2% (2 out of 9) in subjects having psoriasis involvement of > 15% of their BSA. In this study HPA axis suppression was defined as serum cortisol level ≤18 mcg/dL 30-min post cosyntropin stimulation. In the 2 subjects with available follow-up values, suppression reversed 28 days after the end of treatment.

Pharmacokinetics

The extent of percutaneous absorption of topical corticosteroids is determined by many factors including the vehicle, the integrity of the epidermal barrier, and the use of occlusive dressings.

Topical corticosteroids can be absorbed from normal intact skin. Inflammation and/or other disease processes in the skin increase percutaneous absorption. Occlusive dressings substantially increase the percutaneous absorption of topical corticosteroids. Once absorbed through the skin, topical corticosteroids are handled through pharmacokinetic pathways similar to systemically administered corticosteroids. Corticosteroids are bound to plasma proteins in varying degrees. Corticosteroids are metabolized primarily in the liver and are then excreted by the kidneys. Some of the topical corticosteroids and their metabolites are also excreted into the bile.

Plasma concentrations of desoximetasone were measured at two single random time points in the HPA axis suppression trial in 24 subjects with psoriasis [see Clinical Pharmacology ]. The mean (% Coefficient of Variation) concentration of desoximetasone was 449 pg/mL (86%) at Day 14 and 678 pg/mL (135%) at Day 28. The concentration time profile following application of Topicort^® Topical Spray is not known.

NONCLINICAL TOXICOLOGY

Carcinogenesis, Mutagenesis, Impairment of Fertility

Long-term animal studies have not been performed to evaluate the carcinogenic potential of Topicort^® Topical Spray or desoximetasone.

Desoximetasone revealed no evidence of mutagenic or clastogenic potential based on the results of two in vitro genotoxicity tests (Ames assay and Chinese hamster ovary cell chromosome aberration assay) and one in vivo genotoxicity test (mouse bone marrow micronucleus assay).

No evidence of impairment of male or female fertility was observed at subcutaneous desoximetasone doses up to 0.1 mg/kg/day (0.6 mg/m²/day) in Sprague-Dawley rats.

CLINICAL STUDIES

Two multi-center, randomized, double-blind, vehicle- controlled clinical trials were conducted in 239 subjects aged 18 years and older with moderate to severe plaque psoriasis of the body. In both trials, randomized subjects applied Topicort ^® Topical Spray or vehicle spray to the affected areas twice daily for 4 weeks. Enrolled subjects had a minimum body surface area of involvement of 10%, and a Physician's Global Assessment score (PGA) of 3 (moderate) or 4 (severe).

Efficacy was assessed at Week 4 as the proportion of subjects who were considered a Clinical Success ("clear" (0) or "almost clear" (1) according to the PGA scale). Table 2 presents the efficacy results.

Table 2. Number of Subjects (%) with Clinical Success (scored as clear or almost clear) at Week 4.

Parameter	Trial 1		Trial 2
	Topicort® N=59	Vehicle N=60	Topicort® N=60	Vehicle N=60
Clinical Success	18 (30.5%)	3 (5.0%)	32 (53.3%)	11 (18.3%)