title: Intravenous fentanyl kinetics.
abstract: Fentanyl is considered to be a short-acting narcotic analgesic but prolonged and recurrent ventilatory depression has been reported. We examined fentanyl kinetics and excretion in 7 healthy male subjects who were given a 3.2- or 6.4-micrograms/kg dose of 3H-fentanyl intravenously. Arterial blood and urine samples were analyzed for unchanged fentanyl and total radioactivity. Fentanyl concentrations fell rapidly and 98.6% of the dose was eliminated from plasma in 60 min but the terminal elimination phase of fentanyl from the body was slow (t1/2 beta = 219 min) due to the slow return of the unchanged drug from a peripheral compartment to the central compartment where elimination occurred primarily by biotransformation. Eighty-five percent of the dose was recovered in urine and feces in 72 hr; less than 8% was recovered as unchanged fentanyl. There were fluctuations in plasma fentanyl levels during the elimination phase in all cases. The long t1/2 beta and fluctuations in plasma levels may contribute to prolonged and recurrent ventilatory effects of fentanyl.
mesh_terms: D000328:Adult; D001711:Biotransformation; D001798:Blood Proteins / Q000378:metabolism; D002854:Chromatography, Paper; D005243:Feces / Q000032:analysis; D005283:Fentanyl / Q000009:adverse effects / Q000097:blood / Q000378:metabolism* / Q000652:urine; D006801:Humans; D007275:Injections, Intravenous; D007700:Kinetics; D008297:Male; D008657:Metabolic Clearance Rate; D011485:Protein Binding; D012131:Respiratory Insufficiency / Q000139:chemically induced; D013997:Time Factors
chemical_list: D001798:Blood Proteins; D005283:Fentanyl