title: The pharmacokinetics of alfentanil (R39209): a new opioid analgesic.
abstract: The pharmacokinetics of alfentanil (R39209), a new short-acting opioid analgesic, have been studied in eleven patients. Six patients were given 50 micrograms/kg alfentanil and five patients 125 micrograms/kg as an intravenous bolus injection. Plasma concentrations were measured at intervals up to 6 h (50 micrograms/kg) or 8-10 h (125 micrograms/kg), using a specific radioimmunoassay technique. Plasma concentrations declined triexponentially in both groups. The initial elimination of alfentanil from the plasma was very rapid with 90% of the administered dose leaving the plasma within 30 min. The average half-lives for the three phases were similar for both groups. The combined mean (+/- SEM) half-lives for the 11 patients for the rapid and slow distribution phases were short (t 1/2 pi = 1.2 +/- 0.26 min, t 1/2 alpha = 11.6 +/- 1.63 min). The elimination half-life, t 1/2 beta was 94 +/- 5.87 min which is considerably shorter than that of other opioids. The mean (+/- SEM) total body clearance was 6.4 +/- 1.39 ml . kg-1 . min-1 and the volume of distribution (Vd) was 0.86 +/- 0.194 l/kg. The latter is considerably less than reported values for the chemically related drug, fentanyl, and suggests that alfentanil may have a lower tissue binding affinity than fentanyl. The rapid elimination and short duration of clinical action suggests the feasibility of repeated administration of alfentanil and its use by continuous intravenous infusion.
mesh_terms: D000328:Adult; D015760:Alfentanil; D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000097:blood*; D005260:Female; D005283:Fentanyl / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000097:blood; D006207:Half-Life; D006801:Humans; D007275:Injections, Intravenous; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D011863:Radioimmunoassay
chemical_list: D000701:Analgesics, Opioid; D015760:Alfentanil; D005283:Fentanyl