A. Paavola et al., CONTROLLED-RELEASE OF LIDOCAINE FROM INJECTABLE GELS AND EFFICACY IN RAT SCIATIC-NERVE BLOCK, Pharmaceutical research, 12(12), 1995, pp. 1997-2002
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.