Basic Principles of Drug Action and Drug Interactions PDF

Chapter 2 Basic Principles of Drug Action and Drug Interactions Clayton’s Basic Pharmacology for Nurses, 19th edition Michelle Willihnganz, MS, RN, CNE 1  Lesson 2.1 Basic Principles o...

Chapter 2 Basic Principles of Drug Action and Drug Interactions Clayton’s Basic Pharmacology for Nurses, 19th edition Michelle Willihnganz, MS, RN, CNE 1  Lesson 2.1 Basic Principles of Drug Action and Drug Interactions (1 of 3) 1. Identify common drug administration routes. 2. Identify the meaning and significance of the term half-life when used in relation to drug therapy. 3. Describe the process of how a drug is metabolized in the body. 2  Lesson 2.1 Basic Principles of Drug Action and Drug Interactions (2 of 3) 4. Compare and contrast the following terms that are used in relationship to medications: desired action, common adverse effects, serious adverse effects, allergic reactions, and idiosyncratic reactions. 5. Identify what is meant by a drug interaction. 3  Lesson 2.1 Basic Principles of Drug Action and Drug Interactions (3 of 3) 6. Differentiate among the terms additive effect, synergistic effect, antagonistic effect, displacement, interference, and incompatibility. 7. Identify one way in which alternatives in metabolism create drug interactions. 4  Drug Responses in the Body  Drug receptors: Specific sites where drugs form chemical bonds  Pharmacodynamics: Study of interactions between drugs and their receptors and the series of events that result in a pharmacologic response  Agonists: Drugs that interact with a receptor to stimulate a response  Antagonist: Drugs that attach to a receptor but do not stimulate a response 5  Routes of Drug Administration  Enteral: Via the gastrointestinal tract by the oral, rectal, or nasogastric routes  Parenteral: Bypasses the GI tract by using subcutaneous, intramuscular, and intravenous injection  Percutaneous: Absorbed through the skin and mucous membranes  Inhalation, sublingual, or topical 6  Drug Stages After Administration  LADME  Liberation: Drug released from dosage form  Absorption: Depends on route of administration  Distribution: Depends on circulation to be transported throughout body  Metabolism: Depends on enzyme systems  Excretion: Depends on GI tract and kidneys 7  Liberation  Drug released from dosage form and is dissolved in body fluid  Process of converting oral drug can be influenced by food and water in the stomach 8  Audience Response Question 1  All drugs are processed in the body through pharmacokinetics. What is the correct order that drugs pass through the body? a) Liberation, absorption, distribution, metabolism, excretion b) Distribution, metabolism, liberation, absorption, excretion c) Biotransformation, liberation, distribution, absorption, excretion d) Excretion, distribution, liberation, absorption, metabolism 9  Absorption  Drug is transferred from entry site into the body’s circulating fluids  Absorption rate depends on route, blood flow, and solubility of the drug  Subcutaneous and intramuscular injection absorption is affected by circulation  Intravenous medications are absorbed fastest  Topical medications applied to the skin can be influenced by skin thickness and hydration 10  Audience Response Question 2  Which route of administration has the fastest rate of distribution? a) Subcutaneous b) Intramuscular c) Transcutaneous d) Intravenous 11  Distribution  Drugs are transported throughout the body by body fluids to the sites of action  Protein binding and fat solubility affect distribution  Organs with largest blood supply receive the distributed drug most rapidly  Some drugs cannot pass through the blood- brain barrier or the placental barrier 12  Metabolism  The process whereby the body inactivates drugs  Primary organ of metabolism is the liver; other sites are GI tract and lungs 13  Excretion  Elimination of drug metabolites and some of the active drug from the body  Kidneys are the major organ of excretion; some excreted in feces 14  Half-Life of Drugs  Factors modifying the quantity of drug reaching a site of action after a single oral dose 15  Audience Response Question 3  When the nurse administers a 50-mg dose of a drug with a half-life of 6 hours, how many milligrams will remain in the body at 24 hours? a) 25 mg b) 12.5 mg c) 6.25 mg d) 3.13 mg e) 1.56 mg 16  Drug Actions  Onset of action: When the concentration of a drug at the site of action is sufficient to start a physiologic response  Peak action: Time at which the drug reaches the highest concentrations on the target receptor sites  Duration of action: How long the drug has a pharmacologic effect 17  Drug Blood Level  When a drug is circulating in the blood, a blood sample may be drawn and assayed to determine amount of drug present  Important for certain drugs, like anticonvulsants  If drug blood level is low, dosage may be increased; if it is high, dosage must be reduced 18  Adverse Effects of Drugs  Desired action  Side effects  Adverse effects (common and serious)  Idiosyncratic reactions: Occur when something unusual/abnormal happens when drug is first administered  Allergic reactions: Occur among patients who have previously been exposed to a drug and whose immune systems have developed antibodies to the drug 19  Audience Response Question 4  A patient is being started on a new drug that has been used safely by many people for years. The patient has no known allergies, and the nurse administers the drug correctly. Suddenly the patient experiences cardiac arrest. What is this type of reaction called? a) Allergic b) Mutagenic c) Idiosyncratic d) Therapeutic 20  Drug Interactions  Said to occur when the action of one drug is altered or changed by the action of another drug  Elicited in the following two ways:  By agents that, when combined, increase the action of one or both drugs  By agents that, when combined, decrease the effectiveness of one or both drugs 21  Changes in Absorption  Most drug interactions that alter absorption take place in the GI tract  Antacids increase the gastric pH and can inhibit the dissolution of ketoconazole tablets  Many alterations in absorption can be managed by separating the times of administration 22  Changes in Distribution  Many interactions that cause a change in distribution usually affect the binding of a drug to an inactive site  Unbound drugs: Pharmacologically active portion  Drugs are “bound” to proteins in the blood during transportation  The more a drug is bound to a protein, the less available it is to the circulation  Some medications can cause binding or unbinding of another medication, increasing or decreasing its effect 23  Changes in Metabolism  Drug interactions usually result from a change in metabolism that involves inhibiting or inducing the enzymes that metabolize a drug  Serum drug levels usually increase a result of inhibited metabolism when drugs are given concurrently 24  Changes in Excretion  Drug interactions that cause a change in excretion usually act in the kidney tubules by changing the pH to enhance or inhibit excretion 25  Drug Interaction  Additive effect  Synergistic effect  Antagonistic effect  Displacement  Interference  Incompatibility 26  Audience Response Question 5  A patient reports postoperative pain, and the nurse administers morphine (a narcotic analgesic) intravenously to ease the pain. Fifteen minutes later, the nurse notes that the patient is very drowsy, respirations are slow and shallow, and oxygen saturation is low. The nurse administers another drug that decreases the action of the morphine. What is this effect called? a) Displacement b) Antagonistic c) Interference d) Synergistic 27 Questions? 28