Pharmacodynamics - Pharmacokinectics
MEDICAL ANIMATION TRANSCRIPT: Many factors influence the therapeutic efficacy of a drug, including pharmacokinetics, a quantifiable measure of how the body affects the drug. And pharmacodynamics, how the drug affects the body. Pharmacokinetics is a multi-step process that includes absorption or the movement of the drug into the bloodstream. Distribution, or the movement of the drug through the blood and various tissues of the body such as brain tissue, fat, and muscle. Metabolism, or the chemical alteration of the drug by the body. And excretion, or the elimination of the drug by the body. This four-step process is referred to by the acronym ADME. During distribution of certain drugs, proteins present in the bloodstream such as serum albumin bind the drug and render it inaccessible to its target. Effective dose concentration is a measure of unbound drug present in the bloodstream. Thus, pharmacokinetics determines factors within the body that dictate when and how much unbound drug reaches its target site after administration. Pharmacodynamics determines how unbound drug affects the biochemical and molecular interactions of its target macromolecules. This includes activation or inactivation of its target macromolecule, and the specific physiological effects this produces within the body. The first step leading to this response is the interaction of the drug with its target. The target is either specific such as particular receptors or enzymes, or non specific such as neutralizing stomach acids with antiacids. Increasing the dosage of most drugs intensifies the response. Maximal efficacy is the largest possible effect a drug produces. The interaction between pharmacokinetics and pharmacodynamics governs the relationship between the dose of the medication and the desired response. Therefore, pharmacokinetics and pharmacodynamics are pivotal in establishing the therapeutic efficacy of a drug regimen, and producing the desired effect of a drug. Both pharmacokinetics and pharmacodynamics are affected by characteristics unique to each patient, such as genetics and physiological variables such as age.