Effect of repeated injections of chymopapain in the epidural space

Because arachnoiditis occurred in a previous experimental study, the authors performed additional experimental injections of chymopapain in the epidural space. Four monkeys received epidural injections of 100 units of chymopapain in 1.2 mL of saline on days 1, 8, and 16 of the experiment; four control animals received injections of 1.2 mL of 0.9% saline on the same days. Both groups were killed on the 84th day. The dural sac was removed, fixed, sectioned, stained, and examined microscopically. No significant changes were found in the arachnoid, dura, or epidural space of the treated animals. Chymopapain, even if injected repeatedly into the epidural space, does not cause significant scarring in the meninges.