CONTROLLED-RELEASE OF LIDOCAINE FROM INJECTABLE GELS AND EFFICACY IN RAT SCIATIC-NERVE BLOCK

Purpose. Methods of delaying the action of local anesthetics are impor tant, since short duration of action limits their use in the treat men t of postoperative acid chronic pain. The present study evaluated the use of low-viscosity gels in prolonging the release of Lidocaine. Meth ods. Release of lidocaine from 2% lidocaine . HCl containing methylcel lulose (MC), hydroxypropylmethylcellulose (HPMC), sodiumcarboxymethyl cellulose (CMC), and poloxamer 407 (PO) gels was studied in phosphate buffer, pH 7.4, at 37 degrees C. Commercial metylcellulose gel (MC(com )) served as control. The in vivo efficacy of the respective gel formu lations were evaluated in rats. The gel was injected into the vicinity of the sciatic nerve and nociception and motor function were tested. Results. The cumulative amount of lidocaine released during 8 hr was s lowest from the PO gel, followed by the CMC, HPMC and MC gels. The ant inociceptive effect was not prevented by the motor block and lasted lo ngest with the PO gel. Good linear and rank order correlation was obta ined between in vitro and in vivo results. The microscopic examination of the tissue samples revealed only mild or no irritation of the skel etal muscle tissue by the PO, HPMC, and CMC gels. Conclusions. Based o n these results poloxamer gel proved to be the most promising carrier for lidocaine.