Ondansetron, a 5HT3-antagonist, does not alter dynamic mechanical allodynia or spontaneous ongoing pain in peripheral...

The aim of this study was to examine whether the intensity of dynamic mechanical allodynia and spontaneous ongoing pain in patients with neuropathic pain associated with peripheral neuropathy was influenced by an intravenous infusion of the 5HT3-antagonist, ondansetron.

A randomized, double-blind, and placebo-controlled single intravenous infusion of 8 mg ondansetron or saline was administered to 15 patients during 10 minutes on 2 different occasions with an interval of at least 3 days. To monitor the brush-evoked allodynic percept over time, a computerized visual analog scale (VAS) was used allowing the patient to continuously rate the intensity and duration of pain. The area under the VAS curve was used to calculate the total brush-evoked pain intensity. Ongoing pain was rated using a VAS before each assessment of dynamic mechanical allodynia, that is, before and immediately after the infusion and at every 15 minutes over a period of 3 hours.

There was no influence of the factors with or without pain medication and treatment sequence (ie, ondansetron/saline or saline/ondansetron) on brush-evoked or ongoing pain intensity. No significant change over time was found after the infusion of either ondansetron or saline in the total brush-evoked pain intensity, in duration and frequency of aftersensation or in ongoing pain intensity.

No influence from 8 mg of ondansetron could be shown on the intensity of brush-evoked or spontaneous ongoing pain in patients with peripheral neuropathy, indicating the lack of involvement of 5HT3-receptors in an earlier proposed spinobulbospinal loop with descending facilitation acting on spinal mechanisms related to dynamic mechanical allodynia.