Screening for the influence of host factors on warfarin clearance using a single dose single sample procedure.

A single dose, single sample procedure for estimating warfarin clearance for screening purposes was evaluated. Single sample estimates of warfarin clearance, CL/F, were closest to actual values for warfarin clearance, CL/F, calculated from multiple sample data when the sample was collected 120 h after warfarin ingestion. An apparent volume of distribution, V/F, of 0.17 l/kg was used in calculating CL/F. After a single dose of warfarin single sample values of CL/F averaged 0.243 l/h +/- 0.042 (N = 12) which compared well with a multiple sample-based value of CL/F which was 0.243 l/h +/- 0.046 (N = 12). When an erythromycin pretreatment was started before warfarin ingestion and continued throughout the period of warfarin elimination CL/F decreased to 0.208 l/h +/- 0.047 while CL/F decreased to 0.210 l/h +/- 0.061. Mean prediction error for CL/F relative to CL/F was -0.001 l/h with a 95% confidence interval of -0.010 to 0.009 l/h. Warfarin is a drug with pharmacokinetic characteristics enabling it to be used in a single dose single sample procedure in screening for host factor influences on its clearance.