Chapter 2: Drugs And The Body

Chapter 2: Drugs and the Body Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Pharmacodynamics  Pharmacodynamics is the science of dealing with interactions between living organisms and foreign chemicals.  Each living system has chemical reactions occurring continuo...

Chapter 2: Drugs and the Body Copyright © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins Pharmacodynamics  Pharmacodynamics is the science of dealing with interactions between living organisms and foreign chemicals.  Each living system has chemical reactions occurring continuously in the body.  When other chemicals (drugs) are added to the body other effects occur. Copyright © 2017 Wolters Kluwer All Rights Reserved Drug Action  Replace or act as a substitute for missing chemicals  To increase or stimulate certain cellular activities  To depress or slow cellular activities  To interfere with the functioning of foreign cells Copyright © 2017 Wolters Kluwer All Rights Reserved Receptor Sites  Receptor sites react to certain chemicals to cause an effect within the cell.  Agonists  Noncompetitive antagonists-  Competitive antagonists  Drug- enzyme interactions  Selective toxicity Copyright © 2017 Wolters Kluwer All Rights Reserved Lock and Key Copyright © 2017 Wolters Kluwer All Rights Reserved Pharmacokinetics #1  The study of absorption, distribution, metabolism (biotransformation), and excretion of drugs Copyright © 2017 Wolters Kluwer All Rights Reserved Pharmacokinetics #2  Onset of drug action  Drug half-life  Timing of the peak effect  Duration of drug effects  Metabolism or biotransformation of the drug  Site of excretion Copyright © 2017 Wolters Kluwer All Rights Reserved Pharmacokinetics #3 Copyright © 2017 Wolters Kluwer All Rights Reserved Pharmacokinetics #4  Critical Concentration o The amount of a drug that is needed to cause a therapeutic effect  Loading Dose o A higher dose than that usually used for treatment  Dynamic Equilibrium o The actual concentration that a drug reaches in the body Copyright © 2017 Wolters Kluwer All Rights Reserved Dynamic Equilibrium  The actual amount of drug that reaches the body results for a dynamic equilibrium.  Dynamic equilibrium is affected by: o Absorption o Distribution o Biotransformation o Excretion Copyright © 2017 Wolters Kluwer All Rights Reserved Question #1 What is an action of a drug? A. To increase enzymatic reactions in the body B. To alter a missing chemical C. To depress or slow cellular activities D. To increase the effect of foreign substances Copyright © 2017 Wolters Kluwer All Rights Reserved Answer to Question #1 C. To depress or slow cellular activities Rationale: An action of a drug is not to increase enzymatic reactions in the body; alter a missing chemical; nor to increase the effect of foreign substances. Copyright © 2017 Wolters Kluwer All Rights Reserved Absorption #1  What happens to a drug from the time it is introduced to the body until it reaches the circulating fluids and tis- sues Copyright © 2017 Wolters Kluwer All Rights Reserved Absorption #2  Administration o Affected by route of administration o Oral medications affected by presence of food in the stomach  Passive diffusion  Active transport Copyright © 2017 Wolters Kluwer All Rights Reserved Factors Affecting Absorption Copyright © 2017 Wolters Kluwer All Rights Reserved Distribution The movement of a drug to the body’s tissues  Drug’s lipid solubility and ionization- blood brain barrier  Perfusion of the reactive tissue  Placenta/Breast Milk Copyright © 2017 Wolters Kluwer All Rights Reserved Biotransformation  The liver is the single most important site for biotransformation (metabolism).  Breaks down medications  Helps to prevents medications from causing adverse effects on the body  First pass effect Copyright © 2017 Wolters Kluwer All Rights Reserved Excretion  Removal of drugs from the body  Kidneys play the most important role in excretion of medication Copyright © 2017 Wolters Kluwer All Rights Reserved Half-Life #1  Half-life is the time it takes for the amount of drug in the body to decrease to one-half the peak level.  Half-life is affected by absorption, distribution, metabolism, and excretion. Copyright © 2017 Wolters Kluwer All Rights Reserved Half-Life #2 Copyright © 2017 Wolters Kluwer All Rights Reserved Calculating Half-life Copyright © 2017 Wolters Kluwer All Rights Reserved Factors Influencing Drugs Effect  Weight  Genetic Factors  Age  Immunological Factors  Gender  Psychological Factors  Physiological Factors  Environmental Factors  Pathological Factors  Drug Tolerance  Cumulative Effect Copyright © 2017 Wolters Kluwer All Rights Reserved Drug-to-Drug Interactions  Can occur any time two or more drugs are taken together.  Can occur at: o Site of absorption o During distribution o During biotransformation o During excretion o At the site of action Copyright © 2017 Wolters Kluwer All Rights Reserved Drug-Food Interactions  Certain foods interact with drugs  In most cases, drugs are best taken on an empty stomach Copyright © 2017 Wolters Kluwer All Rights Reserved Drug–Laboratory Test Interactions  Drugs may alter the results of lab testing.  Laboratory test may be used to monitor the effects of other medications. Copyright © 2017 Wolters Kluwer All Rights Reserved Question #2 Two patients are receiving injections of penicillin G. One patient is a male, 35 years old, weighing 165 pounds. The other patient is female, 18 years old, weighing 125 pounds. You know that you will see the effects of the drug first in the male patient. What is the rationale for this? A. Women have less fat cells than men B. Men have more vascular muscles than women C. Women have a smaller circulatory system than men D. Drugs are generally tested on healthy males Copyright © 2017 Wolters Kluwer All Rights Reserved Answer to Question #2 B. Men have more vascular muscles than women Rationale: When giving IM injections it is important to remember that men have more vascular muscles, so the effects of the drug will be seen sooner in men than in women. Copyright © 2017 Wolters Kluwer All Rights Reserved