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In this work, we show that alteration of P407 gel content can affect drug release rates. The inorganic salts and PEG 400 commonly included in the formulation of P407 gels can also change the rate at which a drug is released. Lidocaine was selected as a model drug because, although widely used in the treatment of pain, its use is limited by short duration of its effects. The use of P407 gels prolongs the residence time of the lidocaine at the injection site, sustains drug release and increases therapeutic efficacy. Release studies were performed in a diffusion system. During release, data followed the Higuchi square root law time kinetic (r > 0.98). Increased polymer concentration in the gel increases viscosity and reduces lidocaine release rates and diffusion coefficients via extended gel dissolution time and prolonged drug diffusion through the gel matrix. Lidocaine release rates and diffusion coefficients increased in gels composed of NaCl or PEG 400 aqueous solution. Because these additives are hydrophilic, they reduce gel dissolution time, thereby accelerating drug diffusion. Poloxamer is biocompatible and the results support the possibility of using Poloxamer gel as a sustained release injectable formulation.