Kinetic equations steady-state plasma

Since there is a directly proportionate relationship between administered drug dose and steady-state plasma levels Equations 2.2 and 2.3 provide a straightforward guide to dose adjustment for drugs that are eliminated by first-order kinetics. Thus, to double the plasma levels the dose simply should be doubled. Con-versely to halve the plasma level, the dose should be halved. It is for this reason that Equations 2.2 and 2.3 are the most clinically important pharmacokinetic equations. Note that, as is apparent from Eigure 2.6, these equations also stipulate that the steady-state level is determined only by the maintenance dose and elimination clearance. The loading dose does not appear in the equations and does not influence the eventual steady-state level. 

For drugs eliminated by first-order kinetics, the relationship between dosing rate and steady-state plasma concentration is given by rearranging Equation 2.3 as follows ... 

Several drugs, including salicylate (in overdose), alcohol, and possibly some hydrazines and other drugs which are metabolised by acetylation, have saturable elimination kinetics, but the only significant clinical example is phenytoin. With this drug, capacity-limited elimination is complicated further by its low therapeutic index. A 50% increase in the dose of phenytoin can result in a 600% increase in the steady-state blood concentration, and thus expose the patient to potential toxicity. Capacity-limited pathways of elimination lead to plasma concentrations of drugs which can be described by a form of the Michaelis-Menten equation. In such cases, the plasma concentration at steady state is given by... 

Equations (12), simplified by the assumption of isotropic scattering in exciting and dissociating collisions, represent the basic equations for studying many quite different problems in electron kinetics. In particular, the additional simplification to steady-state, purely time-dependent, or purely space-dependent plasma conditions allows a detailed microphysical analysis of various electron kinetic problems related to each of these plasma conditions. 

By the preceding representations, an attempt has been made to give, on the basis of the electron Boltzmann equation, an introduction to the kinetic treatment of the electron component in steady-state, time-dependent, and space-dependent plasmas and to illustrate by selected examples the large variety of electron kinetics in anisothermal weakly ionized plasmas. 

Vibrational distributions in non-equilibrium plasma are mostly controlled by W-exchange and VT-relaxation processes, while excitation by electron impact, chemical reactions, radiation, and so on determine averaged energy balance and temperatures. At steady state, the Fokker-Planck kinetic equation (3-116) gives J(E) = const. At E oo = 0,... 

The balance equations [APP 64] enable us to estabhsh the entropy production rate, from which we deduce the form of the phenomenological relations by way of linearized TIP. Note that with regard to the chemical reactions, there is no need to linearize the stem, because the hterature generally gives us nonlinear chemical kinetic laws with known coefficients (the specific reaction rates). In addition, the balance laws give us the system of equations to be solved in order to determine the fields of variables characterizing the evolution of the plasma in space and time, by means of the knowledge of the physical coefficients. Here, we shall assume steady-state one-dimensional evolution. 

---