Plasma concentrations of meperidine and normeperidine following continuous intrathecal meperidine in patients with neuropathic cancer pain.

Intrathecal administration of meperidine, an opioid with local anesthetic activity, can induce analgesia in patients with intractable cancer pain. However, continuous intrathecal administration may result in the accumulation of normeperidine, responsible for central nervous system toxicity. Ten patients with neuropathic cancer pain, not responding to conventional opioid therapy, were treated with continuous intrathecal administration of meperidine. In all patients, plasma concentrations of meperidine and normeperidine were measured the first days after the start of treatment. Visual analog scale scores were recorded to evaluate pain relief. Quality of life was assessed before and 3 weeks following the start of intrathecal treatment. In three patients the plasma concentrations of meperidine and normeperidine increased rapidly. In one patient the plasma normeperidine concentration was higher than the meperidine concentration. One patient demonstrated transient symptoms suggestive for central nervous system excitation. Three weeks following the start of treatment, seven patients were available for evaluation of their quality of life. Pain relief and overall quality of life improved during the intrathecal treatment. We conclude that continuous intrathecal administration of meperidine alone, or in combination with clonidine, can provide significant pain relief in patients with poor pain control despite pharmacological treatment. However, accumulation of meperidine and normeperidine resulting in central nervous system toxicity may occur during this treatment.