title: Model-based analysis of the pharmacokinetic interactions between ritonavir, nelfinavir, and saquinavir after simultaneous and staggered oral administration.
abstract: Eighteen healthy human immunodeficiency virus-negative subjects participated in an open-label, six-period, incomplete Latin-square crossover pharmacokinetic study. Each subject received two of the three possible pair-wise combinations of single-dose oral ritonavir (R) (400 mg), nelfinavir (N) (750 mg), and saquinavir (S) (800 mg), each pair on three occasions (simultaneous or staggered administration), each occasion at least 2 days after the last. A model-based analysis reveals the following major drug interactions under the conditions of this study: 1). R given simultaneously with S decreases S hepatic intrinsic clearance almost 50-fold relative to that predicted for S given alone and increases its gut bioavailability 90% (but decreases its rate of absorption 40%) relative to when N is given simultaneously; 2). N given simultaneously with S decreases S hepatic intrinsic clearance 10-fold relative to that predicted for S given alone; and 3) R inhibits S hepatic intrinsic clearance even after R plasma levels have become undetectable (>48 h after dosing), implying that R, when used as a pharmacokinetic enhancer, can be dosed less frequently than might be predicted from the duration of detectable systemic concentrations.
authors.affiliation: Department of Biopharmaceutical Sciences, University of California San Francisco, San Francisco, California 94143-0626, USA.
authors.forename: Jian-Feng
authors.initials: JF
authors.lastname: Lu
authors.forename: Terrence F
authors.initials: TF
authors.lastname: Blaschke
authors.forename: Charles
authors.initials: C
authors.lastname: Flexner
authors.forename: Susan L
authors.initials: SL
authors.lastname: Rosenkranz
authors.forename: Lewis B
authors.initials: LB
authors.lastname: Sheiner
mesh_terms: D000284:Administration, Oral; D018592:Cross-Over Studies; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D006801:Humans; D008954:Models, Biological; D008956:Models, Chemical; D019888:Nelfinavir / Q000008:administration & dosage / Q000493:pharmacokinetics*; D019438:Ritonavir / Q000008:administration & dosage / Q000493:pharmacokinetics*; D019258:Saquinavir / Q000008:administration & dosage / Q000493:pharmacokinetics*
chemical_list: D003577:Cytochrome P-450 Enzyme System; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; D019888:Nelfinavir; D019258:Saquinavir; D019438:Ritonavir