Side effects of ketamine in the long-term treatment of neuropathic pain.

OBJECTIVES: Ketamine, noncompetitive antagonist of N-methyl-D-aspartate (NMDA) receptors, has been used in the treatment of chronic neuropathic pain for almost 15 years. The aim of the study was to describe and evaluate side effects of this drug in the group of 32 patients with diabetic polyneuropathy and with postherpetic neuralgia.

DESIGN AND PATIENTS: In total, 32 patients with postherpetic neuralgia and diabetic polyneuropathy were enrolled into our prospective study. The side effects were divided in two groups. First, the side effects observed within 30 minutes lasting intravenuous infusion of 10 mg of ketamine in 100 mL of normal saline. Second after 3 months of peroral treatment of 30 mg of ketamine five times daily.

RESULTS: Sedation was observed in 15.6% of patients after the initial infusion and in 19% of patients in the course of the subsequent oral therapy. In total, 44% (infusion) and 22% (oral administration) of patients reported dizziness. A total of 25% of patients complained about drowsiness and 19% of patients reported dry mouth during oral therapy. In the observed 3-month treatment period, five patients (15.6%) withdrew from the treatment due to a failure of therapy and four patients (12.5%) due to untolerated side effects (dizziness, sedation, loss of appetite, nausea, and vomiting).

CONCLUSIONS: Ketamine is evaluated as a nonoptimal, however, available NMDA blocker suitable for clinical use. Studying its effects in clinics can be expected to increase our knowledge necessary for the development of new, effective, and safe "antineuralgic drug."