Prolongation of epidural bupivacaine analgesia with glycerin.

Glycerin has been used as a drug carrier/depot, but never with local anaesthetics. This study was an attempt to use the slow drug release mechanism to prolong the anaesthetic effects of bupivacaine in epidural block. Twenty-seven adults with cancer pain were prospectively selected according to their primary lesions and problems, but their allocation to study groups was randomized. Group I (n = 13), received 5 ml bupivacaine, 0.125% in normal saline via a previous implanted epidural catheter. When the pain returned to its original intensity, the same amount of the same strength anaesthetic dissolved in 50% glycerin was given via the same catheter. Group II (n = 14) received the same solutions, but in the reverse order. Also five patients in each group received plain 50% glycerin prior to administration of the anaesthetic solutions to serve as controls. The pharmacological effects were assessed by the blinded observers. Analgesia produced with glycerin solution was prolonged compared with the saline solution (12.2 vs 7.2 and 11.6 vs 7.4 hr, P < 0.01). The order of giving the solution did not produce any differences. Plan 50% glycerin did not produce analgesic effects. Neither motor blockade nor other adverse effects or complications were observed in either group. It was concluded that 0.125% bupivacaine in 50% glycerin administered epidurally is not neurotoxic. The prolongation of analgesia observed is attributed to the slow release of bupivacaine from the glycerin base which functions as drug depot. In addition to relief of chronic pain, this novel approach may have other clinical applications such as the relief of labour or postoperative pain.