Transfer functions obtained by the rule of corresponding fractional areas

Summary The transfer of a drug from the compartment in which it is applied to one from which samples can be taken can be determined from time-concentration curves by simple graphical and numerical procedures. The method requires subdivision of the total transferable amount of the drug into four quantities — occupancy, transit, transfer and availment, which can be obtained by an extension of the rule of corresponding areas. Each of these quantities is represented by a fractional area under the experimental time-concentration curve. Subdivision into fractional areas is possible if an additional experiment is performed in which the drug is placed directly in the reference compartment from which the estimations are made. The principle of the method is explained, and its application is demonstrated in examples of the gastrointestinal absorption of iron in children.