Studies on the safety of glucose and paraben-containing neostigmine for intrathecal administration

Initial toxicity testing of neostigmine for intrathecal (IT) injection was performed with preservative-free isobaric solution, yet currently available formulations contain the preservatives methyl- and propylparaben and are usually mixed with glucose to yield hyperbaric solutions. Since it has been proposed that preservatives and hyperbaricity increase the risk of neurotoxicity after IT injection, we examined the safety of chronically administered IT neostigmine containing these additives in sheep and rats. Rats receiving daily IT injections of glucose alone or of glucose with preservative-containing neostigmine, 5 and 10 mu g, exhibited dose-related antinociception, tremor, and rigidity. In comparison to our previously published study of neostigmine injection in solution without glucose, rats receiving IT neostigmine with glucose displayed less rigidity, tremor, and salivation. Sheep receiving daily injection of glucose alone or with preservative-containing neostigmine, 1 mg,for 14 days exhibited no histologic evidence of neurotoxidty, nor did they exhibit abnormalities in cerebrospinal fluid chemistry aside from those caused by inflammation. Spinal cord histologic examination in both species revealed fibrosis and inflammation secondary to the catheter without evidence of neuronal damage. These studies support the safety of paraben- and glucose-containing IT neostigmine.