Historically, the clinician was responsible for information about the sources, physical and chemical properties, compounding, and dispensing of drugs. These activities are now delegated to pharmacologists and pharmacists. Today, the practitioner’s responsibility requires a sound understanding of basic pharmacological principles. These principles apply to all drugs and are predicated on pharmacodynamic, pharmacokinetic, and pharmacotherapeutic variables.

Pharmacodynamics relates to the molecular interactions between body constituents and drugs. It is concerned with issues related to biochemical and physiological mechanisms of drug actions and are based on the concept of drug-receptor interactions. Pharmacodynamics describes the effect of drugs quantitatively in order to determine potency, efficacy, and toxicity. A review of pharmacodynamic principles is presented elsewhere.1

Pharmacokinetics relates to the mechanisms of drug absorption, distribution and redistribution, metabolism or biotransformation, and the excretion or clearance of drugs from the body. Pharmacokinetic variable are important determinants of the dosing regimen required for a drug to reach and maintain therapeutic concentrations in the body for optimum efficacy without causing toxicity. A review of pharmacokinetic principles is presented elsewhere.1