Clobetasone Other names: Clobetasone butyrate

Topical corticosteroids act as anti-inflammatory agents via multiple mechanisms to inhibit late phase allergic reactions including decreasing the density of mast cells, decreasing chemotaxis and activation of eosinophils, decreasing cytokine production by lymphocytes, monocytes, mast cells and eosinophils, and inhibiting the metabolism of arachidonic acid.

Pharmacodynamic effects

Topical corticosteroids, have anti-inflammatory, antipruritic and vasoconstrictive properties.

Clobetasone butyrate has little effect on hypothalamo-pituitary-adrenal function. This was so even when clobetasone butyrate was applied to adults in large amounts under whole body occlusion.

Clobetasone butyrate is less potent than other available corticosteroid preparations and has been shown not to suppress the hypothalamo-pituitary-adrenal axis in patients treated for psoriasis or eczema.

Pharmacological studies in man and animals have shown that clobetasone butyrate has a relatively high level of topical activity accompanied by a low level of systemic activity.

Absorption and Distribution

Topical corticosteroids can be systemically absorbed from intact healthy skin. The extent of percutaneous absorption of topical corticosteroids is determined by many factors, including the vehicle and the integrity of the epidermal barrier. Occlusion, inflammation and/or other disease processes in the skin may also increase percutaneous absorption.

A single application of 30g clobetasone butyrate 0.05% ointment to eight patients resulted in a measurable rise in plasma clobetasone butyrate levels during the first three hours but then the levels gradually decreased. The maximum plasma level reached in the first three hours was 0.6ng/ml. This rise in levels was followed by a more gradual decline with plasma levels of clobetasone butyrate falling below 0.1ng/ml (the lower limit of the assay) after 72 hours. The normal diurnal variation in plasma cortisol levels was not affected by the application of clobetasone butyrate ointment.

The use of pharmacodynamic endpoints for assessing the systemic exposure of topical corticosteroids is necessary due to the fact that circulating levels are well below the level of detection.

Metabolism

Once absorbed through the skin, topical corticosteroids are handled through pharmacokinetic pathways similar to systemically administered corticosteroids. They are metabolised, primarily in the liver.

Elimination

Topical corticosteroids are excreted by the kidneys. In addition, some corticosteroids and their metabolites are also excreted in the bile.

Genotoxicity and Carcinogenesis

Conventional in vitro and in vivo genotoxicity studies reveal no hazard for humans.

Long-term animal studies have not been performed to evaluate the carcinogenic potential of topical clobetasone.

Reproductive toxicity

Topical application of clobetasone to rats at doses of 0.5 or 5 mg/kg/day, and subcutaneous administration to mice at doses ≥3 mg/kg/day or rabbits at doses ≥30 µg/kg/day during pregnancy resulted in foetal abnormalities including cleft palate, intrauterine growth retardation and foetal loss.