Ondansetron Inhibits the Analgesic Effects of Tramadol: A Possible 5-HT3 Spinal Receptor Involvement in Acute Pain in Humans

Abstract

Serotonin is an important neurotransmitter of the descending pathways that down-modulate spinal nociception. In postoperative pain, ondansetron, a selective 5-HT(3) receptor antagonist, increased the analgesic dose of tramadol. We suggest that, when antagonized for antiemetic purpose, 5-HT(3) receptors foster nociception, because of their site-dependent action.