Why are different strengths critical? The appropriate strength depends on many factors. For example, babies absorb topical steroids faster than adults, so they may require a low-potency steroid. Areas of the body where skin touches skin (think: armpits, rectal area, etc), as well as sensitive areas (like the skin on the eyelids), tend to absorb topical steroids more rapidly, so those regions of the body also usually require a low-potency steroid. However, thick, rough skin on the palms of the hands and the soles of the feet usually absorb topical steroids more slowly than other parts of the body, so those areas typically require a more potent steroid. Keep in mind: The greater the potency of the steroid (in other words, the lower its class number), the more likely it is to cause side effects .
The most common side effect of topical corticosteroid use is skin atrophy. All topical steroids can induce atrophy, but higher potency steroids, occlusion, thinner skin, and older patient age increase the risk. The face, the backs of the hands, and intertriginous areas are particularly susceptible. Resolution often occurs after discontinuing use of these agents, but it may take months. Concurrent use of topical tretinoin (Retin-A) % may reduce the incidence of atrophy from chronic steroid applications. 30 Other side effects from topical steroids include permanent dermal atrophy, telangiectasia, and striae.
No metabolites of fluticasone propionate were detected in an in vitro study of radiolabeled fluticasone propionate incubated in a human skin homogenate. The total blood clearance of systemically absorbed fluticasone propionate averages 1,093 mL/min (range, 618 to 1,702 mL/min) after a 1-mg intravenous dose, with renal clearance accounting for less than % of the total. Fluticasone propionate is metabolized in the liver by cytochrome P450 3A4-mediated hydrolysis of the 5- fluoromethyl carbothioate grouping. This transformation occurs in 1 metabolic step to produce the inactive17-ÃŸ-carboxylic acid metabolite, the only known metabolite detected in man. This metabolite has approximately 2,000 times less affinity than the parent drug for the glucocorticoid receptor of human lung cytosol in vitro and negligible pharmacological activity in animal studies. Other metabolites detected in vitro using cultured human hepatoma cells have not been detected in man.