title: Pharmacokinetics of flunitrazepam in rats studied by a radioreceptor assay.
abstract: In rat the kinetics of flunitrazepam (FNZ) was evaluated by a radioreceptor assay (RRA) after i.v. administration of 1 mg/kg and after oral administration of 1 and 3 mg/kg. The i.v. kinetics is biexponential and the g.i. absorption is very rapid (with a plasma peak at 0.25 hour) with a good bioavailability (69%); the apparent distribution volume is high, 4.8 L/kg; the half-life is equal to 3.5 hours; the elimination constant is equal to 0.8 h-1; the urinary excretion of FNZ-equivalent is negligible; the plasma total clearance is equal to 3.9 (L/kg)h-1. The concentrations of FNZ-equivalents after oral administration of 1 mg/kg show a peak at the 2-nd hour with a very high concentration in the following organs (in decreasing order): brain, kidneys, heart, liver; after 8 hours no FNZ-equivalents are present in these organs except in the brain, which shows detectable concentrations at the 32-nd hour. The peak concentrations of FNZ-equivalent in brain, kidneys and heart are higher than the corresponding peak concentration in plasma.
mesh_terms: D000818:Animals; D005445:Flunitrazepam / Q000378:metabolism*; D066298:In Vitro Techniques; D007408:Intestinal Absorption; D007700:Kinetics; D008297:Male; D011869:Radioligand Assay; D051381:Rats; D011919:Rats, Inbred Strains; D014018:Tissue Distribution
chemical_list: D005445:Flunitrazepam