Rheological characterization of Poloxamer 407 lidocaine hydrochloride gels

Thermal gelation of Poloxamer 407 lidocaine hydrochloride gels was characterized by rheological studies. Lidocaine, a local anesthetic used for treatment of acute and chronic pain, presents short duration action thus a long-action single-dose injection would be of clinical importance. Poloxamer 407 gel can extend the release and the action of lidocaine. In the present work aqueous gels with lidocaine containing different concentrations of Poloxamer 407 and additives like inorganic salts (NaCl, NaH2PO4, Na2CO3) and PEG 400 were obtained. Viscosity measurements and the optimal sol-gel transition temperature were obtained by these rheological studies. Poloxamer 407 gels are viscoelastic materials because they have elastic modulus (G'), characteristic of solid materials, and viscous modulus (G), characteristic of liquid materials. Poloxamer 407 gels are pseudoplastic: therefore when shear deformed their viscosity decreases. Increase of the polymer concentration increases the viscosity of the gels, which can change the releasing process of lidocaine front the gel. The sol-gel transition temperature was decreased by increasing the polymer concentration and by the presence of additives. The rheological behaviour of Poloxamer gels characterized in this work can be useful for understanding further studies of drug release. (C) 2002 Elsevier Science B.V. All rights reserved.