Pharmacokinetics
Note that you will not be tested on this section in the end-of-course quiz.
AMU and the design of effective dosage regimens are based on the relationship between the administered dose of a drug, the resulting drug concentrations in various body fluids and tissues, and the intensity of pharmacologic effects caused by these concentrations. The journey of the antimicrobial through the body occurs in steps: absorption, distribution, metabolism and elimination (ADME). This is shown in Figure 5 and described in more detail below.
Absorption
Most antimicrobials are administered orally; various factors affect their ability to achieve the expected activity. Absorption is complex and involves several possible mechanisms. Passive diffusion has been identified as the predominant mechanism of gastrointestinal absorption for most drugs. Physiological characteristics such as gastric emptying time and pH conditions throughout the gastrointestinal tract also affect oral absorption. The presence of food, other drugs and certain digestive disorders may further change the rate and extent of absorption.
Distribution
Once a drug has entered the vascular system, it becomes distributed throughout the various tissues and body fluids. However, most drugs do not distribute uniformly throughout the body: their distribution is based on tissue-specific differences in rate and extent of drug uptake, including blood flow and the delivery of drug to the tissues.
Metabolism
Elimination of drugs occurs by metabolism and excretion. Metabolism of antimicrobials converts them to more water-soluble metabolites that are readily excreted into the urine or bile. Drug metabolism usually involves multiple pathways and a particular drug may simultaneously undergo metabolism by several competing pathways: formation of specific metabolites is determined by the relative rates and affinities of each of the parallel pathways. Metabolic conversion usually decreases or diminishes the pharmacologic activity of a drug, but depending on the structure/activity relationship for the drug target, metabolites may have similar or even higher activity than their parent compound.
Excretion
Excretion of antimicrobials or their metabolites can take place through numerous pathways (kidney, liver, lung, skin, etc.), but the most significant organ for excretion is the kidney.
Dosing and dose adjustment
