Abstract: AIM: Based on probability theory, two concrete methods for absorption kinetics were proposed in one-compartmental model.METHODS: After an extravascular administration of drug, total resident time (T_h) was regarded as sum of the resident time in site of administration (T_f) and the resident time in body (T_g). Not only are T_f and Tg independent each other, T_f, T_g and T_h are nonnegative, continuous random variables also. According to convolution formula and characterization of one-compartmental model (exponential distribution), methods of probability theory for calculating the absorption rate of drug were obtained. These methods were composed of probability method (A approach) and numerical deconvolution method (B approach).RESULTS: The essential conditions of method of probability theory were in accordance with that of Wagner-Nelson (W-N) formula. The accuracy of A approach was identical with that of W-N formula. As long as the accurate value of first-order elimination rate constant (K) can be estimated, the accuracy of B approach was inferior to that of W-N formula. In case K value with relative error (±10%) was calculated, the accuracy of B approach was slightly superior to that of W-N formula.CONCLUSION: Method of probability theory can be suggested to estimate the percentage of drug absorbed and the concerned probability.

Key words: Pharmacokinetics, One-compartmental model, Absorption kinetics, Probability theory, Random vector, Numerical deconvolution, Exponential distribution, Probability density function, Distribution function