[Transdermal delivery of drugs and enhancement of percutaneous absorption]

Transdermal delivery systems in cosmetics

Transdermal delivery systems have been intensively studied over the past 2 decades, with the focus on overcoming the skin barrier for more effective application of pharmaceutical and cosmetic products. Although the cosmeceutical industry has made a substantial progress in the development and incorporation of new and effective actives in their products, the barrier function of the skin remains a limiting factor in the penetration and absorption of these actives. Enhancement via modification of the stratum corneum by hydration, acting of chemical enhancers on the structure of stratum corneum lipids, and partitioning and solubility effects are described. This review summarizes the advances in the development and mechanisms of action of chemical components that act as permeation enhancers, as well as the advances in appropriate vehicles, such as gels, emulsions, and vesicular delivery systems, that can be used for effective transdermal delivery.

Comparison of serum dexamethasone concentrations in cats after oral or transdermal administration using pluronic lecithin organogel (PLO): a pilot study

The objective of this study was to measure and compare the serum concentrations of dexamethasone after oral and transdermal administration using pluronic lecithin organogel in six healthy cats. The study was designed as a crossover, in which the cats were randomly assigned to two groups. The cats received a single dose (0.05 mg kg(-1)) of dexamethasone either orally or transdermally on the inner pinna. Blood samples were taken at 0, 5, 15, 30, 60, 90 and 120 min, and 3, 4, 6, 8, 12 and 24, 48 and 72 h post dexamethasone administration. A mean peak serum concentration of 30.1 ng mL(-1) was detected 15 min after oral administration. Serum concentrations were below detection limits by 24 h. In contrast, there was no significant increase in serum concentrations of dexamethasone after transdermal administration. In cats, transdermal administration of a single dose of dexamethasone did not result in significant serum concentrations compared to oral administration.

Alpha-monoisostearyl glyceryl ether enhances percutaneous penetration of indometacin in-vivo

Molecules that reversibly remove the barrier resistance of skin enhance penetration. alpha-Monoisostearyl glyceryl ether (GE-IS) is a novel compound that can be used as a non-ionic surfactant and increases percutaneous penetration of indometacin in rat abdominal skin in-vitro. The present study investigated GE-IS-induced enhancement of indometacin penetration in-vivo. When 1% GE-IS in propylene glycol was applied to rat abdominal skin, serum and muscle concentrations of indometacin increased markedly. Anti-inflammatory activities of test solutions containing both indometacin and GE-IS were investigated in experimental models of acute and chronic inflammation. Application of indometacin with GE-IS to the skin produced greater inhibitory effects on carrageenan-induced rat paw oedema, UV-induced erythema in guinea-pigs, and adjuvant arthritis in rats, compared with application of indometacin alone. The results suggest that GE-IS enhances penetration in-vivo and improves the anti-inflammatory effects of indometacin in animal models. Thus, GE-IS might contribute to the development of cosmetic or medical formulations to improve transfer of bioactive substances to hypodermal sites.

Bioavailability of transdermal methimazole in a pluronic lecithin organogel (PLO) in healthy cats

The antithyroid drug methimazole is widely used for the medical management of feline hyperthyroidism. Recently, custom veterinary pharmacies have offered methimazole in a transdermal gel containing pluronic and lecithin (PLO), with anecdotal evidence of efficacy. The purpose of this study was to determine the bioavailability, relative to i.v. and oral routes of administration, of transdermal methimazole in a PLO gel in cats. Six healthy adult cats were assigned to receive 5 mg of methimazole by the i.v., oral, or transdermal routes, in a randomized triple crossover protocol with 1 week washout between doses. Blood samples were taken for high performance liquid chromatography (HPLC) determination of serum methimazole, at 0, 5, 15, 30, 60 min, and 2, 4, 6, 12 and 24 h after dosing. Methimazole absorption following transdermal administration was poor and variable, with only two of six cats achieving detectable serum methimazole concentrations at any time point following transdermal administration. Area under the concentration-time curve (AUC), maximum concentration (Cmax), and absolute bioavailability were all significantly lower for the transdermal route (0.39 +/- 0.63 microg h/mL, 0.05 +/- 0.09 microg/mL, and 11.4 +/- 18.7%, respectively) than for either i.v. (7.96 +/- 4.38 microg h/mL, 3.34 +/- 2.00 microg/mL, 100%) or oral routes (2.94 +/- 1.24 microg h/mL, 0.51 +/- 0.15 microg/mL, 40.4 +/- 8.1%). The results of this study indicate generally low to undetectable bioavailability of methimazole in a lecithin/pluronic gel given as a single transdermal dose to healthy cats, although one individual cat did achieve nearly 100% transdermal bioavailability relative to the oral route.