title: Significance of ratios of different volumes of distribution in pharmacokinetics.
abstract: Multicompartmental pharmacokinetics involves the four volumes: Vc = volume of the central compartment; Vss = volume of distribution steady-state; V beta = volume of distribution beta; and Vext = the extrapolated volume of distribution. The ratio Vc/Vext is indicative of the degree of multicompartmental character of a set of data. The quantity (Vext/V beta)--1 is the fractional error in the total clearance when one assumes a monoexponential rather than a polyexponential equation for disposition of a drug. The ratio Vss/V beta indicates how well the one-compartment body model predicts average amounts of drug in the body when a multicompartmental model is actually operative. The quantity (Vss/Vc)--1 is equal to either k12/k21 or k12/k21 + k13/k31 of the two- and three-compartmental mammillary models. Examples from the literature are reported and discussed.
mesh_terms: D000284:Administration, Oral; D001682:Biological Availability; D002440:Cefoxitin / Q000378:metabolism; D004077:Digoxin / Q000378:metabolism; D006801:Humans; D007275:Injections, Intravenous; D007700:Kinetics; D008433:Mathematics; D008954:Models, Biological; D010424:Pentobarbital / Q000378:metabolism; D004364:Pharmaceutical Preparations / Q000378:metabolism*
chemical_list: D004364:Pharmaceutical Preparations; D002440:Cefoxitin; D004077:Digoxin; D010424:Pentobarbital