The pharmacokinetic phase

Dmg transport during the pharmacokinetic phase represents a compromise between the increased solubility of the ionized form of a drug and the increased ability of the non-ionized form to penetrate the lipid bilayer of cell membranes. A drug must cross many lipid barriers as it travels to the receptor that is its site of action. Yet cell membranes... 

The pharmacokinetics of a drug can also change with aging and disease (8, 20, 26, 29, 32, 64, 65, 66, 67, 68, 69 and 70). Several factors can alter the pharmacokinetic phases in the elderly, making them more prone to psychotropics effects, including the following ... 

The pharmacokinetic phase of drug action includes the Absorption, Distribution, Metabolism and Elimination (ADME) of the drug. Many of the factors that influence drug action apply to all aspects of the pharmacokinetic phase. Solubility (see Section 3.3), for example, is an important factor in the absorption, distribution and elimination of a drug. Furthermore, the rate of drug dissolution, that is, the rate at which a solid drug dissolves in the aqueous medium, controls its activity when a solid drug is administered by enteral routes (see Section 2.6) as a solid or suspension. 

For definitions see Section 2.7. The factors affecting the pharmacokinetic phase are ADME. The factor affecting the pharmacodynamic phase is the stereoelectronic structure of the drug molecule. 

In both pharmacokinetic and pharmacodynamic considerations, an important emphasis concerns the rate at which events occur and the rate at which circumstances change. The pharmacokinetic phase covers the relationship between drug input and the concentration achieved over time. The pharmacodynamic phase covers the relationship between concentration and the therapeutic effect over time (toxicodynamics is concerned with the relationship between concentration and adverse effects over time). 

With regard to the pharmacokinetic phase of action, a distinction can be made between distribution over the various compartments or tissues, and the time-concentration relationship in particular compartments. Modulation of the pharmacokinetics by suitable molecular manipulation is important at an early stage in the design procedure. Here a distinction can be made between the modulation of the rate and possibly the site of bioinactivation or bioactivation, and modulation of the distribution, including the rate of absorption and rate of elimination. 

The pharmacokinetic phase controls the different parameters that govern the random walk of the drug between its application point and its final site of action and which ensure the destruction and/or the elimination once the effect is produced. The site of action is often separated in space and... 

Dmg activity is divided into the pharmaceutic phase, pharmacokinetic phase and the pharmacodynamic phase. The pharmaceutic phase is the disintegration and dissolution of a dmg taken orally. The pharmacokinetic phase is the mechanism used to absorb, distribute, and eliminate a dmg. The pharmacodynamics is a dmg s effect on the physiology of the ceU and the mechanism that causes the pharmaceutical response. 

Human and veterinary pharmaceuticals are often highly metabohzed before they are excreted into wastewater or the environment. Thus, we have to consider both the metabohsm during the pharmacokinetic phase in the target organism and the environmental transformation processes. For simphcity, we focus in the following on the metabohtes formed in organisms, but environmental transformation products could be treated in an analogous way as the pesticides discussed above. Also veterinary and human pharmaceuticals can be approached in a similar fashion but the examples below refer to human pharmaceuticals. 

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