A mixture of both first-order and zero-order kinetics is observed in such cases and therefore the process is said to follow mixed-order kinetics. Since deviations from an originally linear pharmacokinetic profile are observed, the rate process of such a drug is called as nonlinear kinetics.
Mixed-Order Kinetics (Nonlinear Kinetics)
In some instances, the kinetics of a
pharmacokinetic process changes from predominantly first-order to predominantly
zero-order with increasing dose or chronic medication. A mixture of both first-order and zero-order kinetics is observed in
such cases and therefore the process
is said to follow mixed-order kinetics.
Since deviations from an originally linear pharmacokinetic profile are
observed, the rate process of such a drug is called as nonlinear kinetics. Mixed order kinetics is also termed as dose-dependent kinetics as it is
observed at increased or multiple doses of some drugs. Nonlinearities in
pharmacokinetics have been observed in –
·
Drug absorption (e.g. vitamin C)
·
Drug distribution (e.g.
naproxen), and
·
Drug elimination (e.g.
riboflavin).
The phenomena is seen when a particular
pharmacokinetic process involves presence of carriers or enzymes which are
substrate specific and have definite capacities and can get saturated at high
drug concentrations (i.e. capacity-limited). The kinetics of such
capacity-limited processes can be described by the Michaelis-Menten kinetics.
Related Topics
TH 2019 - 2023 pharmacy180.com; Developed by Therithal info.