Continuous sampling as a pharmacokinetic tool.

Continuous sampling (CS) of blood through a nonthrombogenic catheter is presented as a tool for determining various pharmacokinetic parameters after a single injection of a drug. In addition to defining many of the usual parameters used in pharmacokinetic analyses, CS provides an accurate and direct determination of the total area under the plasma concentration curve. The theoretic background underlying the CS method is derived, and a practical formulation for its use in a clinical setting is described. The aminoglycoside antibiotic, amikacin, was chosen to exemplify the use of this technique. The drug was administered to 6 children, and CS was used to define plasma and single organ (kidney) clearance, volume of distribution, half-life during the final elimination phase, the shape of the plasma concentration curve, and the exponential factorization of this curve for multicompartmental analysis. The CS method has several theoretical and practical advantages over the usual technique of intermittent blood sampling; such as accuracy in the determination of the plasma concentration-time curve integral, relative model independence, requirement for few samples, and ease in obtaining samples.