Ch. 4 Pharmacokinetics Notes PDF

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Ch. 4 Pharmacokinetics 4.1 Pharmacokinetics: How the Body Handles Medications  The study of drug movement throughout the body  There are four categories o Absorptions o Distribution o Metabolism o Excretion 4.2 The Passage of Drugs Through Plasma Membranes  Drugs must penetrate plasma membranes to produce their effects  Two process to cross body membranes o Active transport  against the concentration gradient requiring energy o Diffusion or passive transport  higher to lower concentration without the use of energy 4.3 Absorption of Medications  Absorption  the movement of a substance from the site of administration, across body membranes, to circulating fluids o Primary pharmacokinetic factor determining the length of time it takes a drug to produce its effects o Factors affecting drug absorption  Drug formulation and dose  Dose  Route of administration  Size of drug molecule  Surface area of absorptive site  Digestive motility  Blood flow  Lipid solubility of drug  Dissolution  determines how quickly the drug disintegrates and disperses into simpler forms 4.4 Distribution of Medications  Distribution  involves the transport of drugs throughout the body after they have been o Simplest factor determining distribution is the amount of blood flow to body tissues o The more blood flow to the area (heart, liver, kidney, brain), the higher the concentration of the drug. o Lowest blood flow areas are skin, bone, adipose tissue o Blood-brain barrier  anatomic barrier that prevent many chemicals and medications from entering  Cancer drugs do not easily cross this barrier o Fetal-placental barrier  prevents harmful substances from passing from the mother to the fetus  Many substances such as alcohol, cocaine, caffeine and certain meds do cross easily

o Several types of drug-drug interactions  Addition  the action of drugs taken together as a total  Synergism  the actions of drugs resulting in a potentiated effect  Antagonism  drugs taken together with blocked or opposite side effects  Displacement  when drugs are taken together, one drug may shift another drug at a nonspecific protein-binding site, altering the desired effect 4.5 Metabolism of Medications  Metabolism (biotransformation)  The chemical process of changing a drug to a form the body can easily remove from the body.  First-Pass Effect: o Drug is absorbed, enters the liver, enzymes change drugs to inactive forms, & leaves the liver to be distributed to the circulation. o Many drugs are rendered inactive by first-pass effect  Metabolic activity may be decreased in some situations: o Infants and elderly o Severe liver disease o Certain genetic disorders 4.6 Excretion of Medications  Excretion  the process by which drugs are removed from the body.  Primary site of excretion is the kidney. o Can also be excreted into bile  Called biliary excretion  Drugs secreted into the bile will enter the duodenum and then soon leave the body in the feces o Can be excreted by the lungs  The lungs excrete most drugs in their original nonmetabolized form o Can be excreted by glandular secretions  Water-soluble drugs may be secreted into the saliva, sweat, or breast milk o Also excreted by the respiratory system  Kidney dysfunction or disease can lead to toxic levels of a drug.  Factors affecting excretion o For drugs excreted in bile…. o Bile recirculates to liver Percentage of drug may be recirculated numerous times (called enterohepatic recirculation) o Prolongs activity of drug  Activity of drug may last after discontinuation

4.7 Drug Plasma Concentration & the Therapeutic Effect  Therapeutic response of most drugs is often related to their level in the plasma  Concentration of medication at target tissue is often impossible to measure, so it must be measured in plasma  Minimum effective concentration  amount of drug required to produce a therapeutic effect  Toxic concentration  level of drug that will result in serious adverse effects  Therapeutic range  plasma drug concentration between the minimum effective concentration and the toxic concentration 4.8 Onset, Peak Levels & Duration of Drug Action  Half-life  Length of time needed to decrease drug plasma concentration by one half o The greater the half-life, the longer it takes to excrete o This determines frequency and dosage 4.9 Loading Doses & Maintenance Doses  Dosing o Repeated dosing results in an accumulation of the drug.  Loading dose o Giving an initial higher dose of the med will help reach the plateau quicker.  Maintenance dose o Given at intervals to keep the drug concentration in the therapeutic range.  Therapeutic response o of drugs is dependent on the concentration of the drug in the blood.  Therapeutic range o is the concentration between the minimum effective level and the toxic level....