• Serotonin syndrome is characterized by confusion, agitation, tachycardia, fever, hyperreflexia, and myoclonus. Normeperidine is an active metabolite of meperidine metabolism and has a half-life of 15 to 30 hours in an adult. Normeperidine’s elimination is dependent upon renal function and can accumulate with high repeated dosages or in the presence of renal impairment. Serotonin antagonists, SSRI and tricyclic antidepressants all may enhance the adverse/toxic effects of meperidine that results in serotonin syndrome.