A retrospective study of the pharmacokinetics of heparin

The published data on pharmacokinetics of intravenously administered heparin were studied by computer analysis. The relative volume(s) of distribution (RVD) and plasma half‐life (t ½ ) were calculated for men, dogs, and rabbits. All 57 log plasma heparin concentration‐time curves fitted equations for first‐order processes, even at the largest doses. In dogs, both the RVD and t ½ varied with the dose and with each other, regardless of dose; in men, only the t ½ varied with dose. The t ½ in men increased to a greater extent per unit increment in dose than in dogs. In both species, the RVD corresponded to the plasma volume, except with very large doses. The data were consistent with the hypothesis that heparin may leave the plasma by uptake into the reticuloendothelial system. They explain some of the difficulties in devising practical and reliable clinical dose schedules for heparin.