Evaluation of low strengths topical dosage forms of lidocaine with enhanced drug release profiles

This study was undertaken to screen various formulations for the in-vitro release of Lidocaine from various topical bases including a gel, Hydrophilic Ointment base, HPMC gel, Aquaphor and Petrolatum bases. Various ingredients known to enhance the drug release from the topical bases were also evaluated at various concentration levels. These included Ethanol, Propylene Glycol and Diethylene Glycol Monoethyl ether. The formulations containing 2.5% and 1.25% of Lidocaine and penetration enhancing ingredients at various levels were prepared and evaluated for their in-vitro drug release profiles. For comparison purposes, a commercial ointment containing 5% drug was included as a control. One gram sample of each formulation was placed in the donor compartment, and the in-vitro drug was determined by using Franz diffusion cells through the cellulose membrane for up to 2 hour period.;The general rank order for the drug release was observed to be: Hydrophilic Ointment > Aquaphor > Carbopol > HPMC > Petrolatum base.;Among all the formulations evaluated, the lowest strength sample containing 1.25% drug, made with the Hydrophilic ointment and 20% ethanol as the additive gave the optimum release of drug. This formulation with the maximum in-vitro release through the cellulose membrane was further evaluated for the in-vitro release of drug through the cadaver skin. Here again, the optimum formulation exhibited the maximum drug release and the data correlated well with the in-vitro results obtained through cellulose membrane.;The in-vitro release data were treated with various kinetic principles to determine relevant parameters, such as steady-state flux, diffusion, and permeability coefficient values and these correlated well with amount of drug release.;This study supports the fact that with a proper vehicle, it is possible to dermatological formulation of such a clinically important drug with significantly reduced levels of the active ingredient.