PERCUTANEOUS ABSORPTION OF ANALGESICS IN THE PRESENCE OF PERMEATION ENHANCERS

Abstract

The transdermal route has been recognized as a highly potential route of systemic drug delivery and provides the advantage of avoidance of the first-pass effect, ease of use and withdrawal (in case of side-effects), and better patient-compliance. However, the major limitation of this route is the difficulty of permeation of drug through the skin which can be improved by the use of penetration enhancers. Studies have been carried out to find safe and suitable permeation enhancers to promote the percutaneous absorption of drugs. The aim of present study was to evaluate the effect of various enhancers on percutaneous absorption of Diclofenac Diethylamine (DDA) across silicone membrane and full thickness rabbit skin. The enhancers used in this study were propylene glycol (PG), polyethylene glycol (PEG 400), Glycerol (Gly), Oleic acid (OA) and Turpentine oil (TO). DDA was chosen as a lipophilic drug having a molecular weight of 316.7 and partition coefficient (Ko/w) of 4.40. Prior to start the diffusional experiments, the solubility studies were conducted for the saturated solutions and their concentrations at 1, 2, 3 & 4% (v/v) each of these enhancers. The enhancing effect of enhancers was found to be significantly greater than that of standard without enhancer (control). Diffusional experiments were conducted using modified Franz-diffusion cell across silicone membrane and full thickness rabbit skin, with constant stirring of receptor phase containing phosphate buffered saline (PBS) as receptor solution (pH 7.4±0.1) at 37°C±2. 1 ml of sample was applied in the donor compartment for diffusional studies across silicone membrane while 20 ml of sample was applied in the donor compartment in case of rabbit skin experiments. ‘Benchmark’ parameters with which to compare the performance of the other vehicles are the flux values and these values from propylene glycol (PG), polyethylene glycol (PEG) and glycerol (Gly) have statistically insignificant difference (P>0.05) in their saturated solutions across silicone membrane whereas all Flux values for saturated enhancer’s solutions are statistically insignificant except values for Glycerol which are significantly high across rabbit skin only. To explain the difference in values of flux between saturated and control may be the differential uptake of enhancer’s by the SC of the skin, while flux values for all concentrations of enhancer’s across rabbit skin were statistically significant (P<0.05) and on the basis of these values it can be recommended that the 4% concentrations of the enhancers used can be best formulated DDA in a topical product. The input-rate of all the enhancers has shown a trend of increase with the increase in the enhancer’s solution concentrations. The DDA binary formulations showed the significantly high permeation rate and the content of enhancers’ concentration in formulations influenced the skin permeation rate substantially for DDA. As the content of enhancers’ concentration was decreased from 4% to 1% of DDA binary formulations, the skin permeation rate of DDA also decreased which may be due to thermodynamic activity of drug in the formulation as DDA is poorly water soluble (~42.28mg/ml at 37°C±2) and yet solublised in the enhancers’ mixture. Data from permeation experiments revealed that the DDA permeated across membrane/or skin at a faster rate in the presence of PG and PEG than the other vehicles studied. This finding was in line with evidence from Franz-type diffusion experiments in which flux was consistently higher from formulations. On the basis of flux values that solutions made by PG and PEG as enhancers may be recommended to formulate topical preparations. The vehicles used were predominantly influencing the partition of the drug into the rabbit skin rather than the diffusion throughout the study. Consequently, changes in diffusion and/or partition may occur as a result of absorption or depletion of permeation enhancers inside the membrane/or skin over time which validates our results.