Research Articles
Precursor-dependent indirect pharmacodynamic response model for tolerance and rebound phenomena

https://doi.org/10.1021/js980171qGet rights and content

Abstract

A precursor-dependent model of indirect pharmacody-namic response which can describe tolerance and rebound was characterized in terms of the effects of changes in the fundamental properties of the drug on its response profiles. The model extends previous models by considering inhibition or stimulation of production of the response variable dependent on the amount of precursor which may accumulate or deplete after administration of some drugs. Standardized pharmacokinetic and pharmacodynamic parameters were used for generating dose, plasma concentration, and response–time profiles using computer simulations. The peak response (Rmax) and the time of its occurrence (TRmax) were dependent on the dose, degree of maximum inhibition (Imax) or stimulation (Smax), and drug concentrations causing 50% inhibition (IC50) or stimulation (SC50). The maximum rebound (RBmax) and the time of its occurrence (TRBmax) after a single bolus dose were also dependent on these factors, but were of lesser magnitude and showed relatively later occurrence. Interestingly, values of area between the baseline and effect curve (ABEC) and area between the baseline and rebound curve (ABRC) were equal for each set of conditions for each model, but the latter is reduced when there is a second pathway for loss of precursor. Tolerance occurs because of diverse mechanisms, and the response patterns demonstrated may be helpful in describing tolerance and rebound phenomena for drugs which affect precursor pools.

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    Citation Excerpt :

    In their most basic form these models are based on the concept of a physiological indirect response or turnover model as originally proposed by Levy to describe the time course of the anticoagulant effect of warfarin (Nagashima et al., 1969). Jusko et al. have subsequently formalized the concept of using various forms of a turnover model to characterize time-dependencies in the pharmacodynamics of a wide range of drugs (Dayneka et al., 1993; Jusko, 1995; Jusko and Ko, 1994; Sharma et al., 1998). Here, the drug effect is being characterized as an enhancing or inhibiting effect on either the zero order rate constant for input in the system or the first order rate constant for elimination from the system (Dayneka et al., 1993).

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Supported in part by Grant No. 24211 from the National Institute of General Medical Science, National Institutes of Health.

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