The investigators hypothesize that co-administration of a 5-HT3 receptor antagonist ondansetron (single 16mg dose) with p-glycoprotein inhibitor tariquidar (single 4mg/kg dose) vs placebo in a cross-over prospective randomized study, will:~Be tolerable in patients with neuropathic pain.~Increase the cerebrospinal fluid (CSF) to plasma ratio of ondansetron after intravenous administration, compare to ondansetron alone~Result in a greater reduction in pain intensity than with ondansetron alone.
Prospective, randomized, double-blind, placebo controlled, cross-over proof of concept study.~To determine the pharmacokinetics and tolerability of co-administration of 5-HT3R antagonist ondansetron with a P-glycoprotein inhibitor tariquidar, in patients with neuropathic pain.