Clinical Significance of Plasma Drug Levels

Chapter 4 Pharmacokinetics Learning Objectives: 1. List the four main processes that make up pharmacokinetics. ● The four main processes that make up pharmacokinetics are absorption, distribution, metabolism, and excretion. Chapter 4 reading: Pharmacokinetics is the study of how drugs move throughout the body, including processes like absorption, distribution, metabolism, and excretion. Understanding pharmacokinetics is crucial in maximizing the benefits of drug therapy and minimizing harm. By applying this knowledge, healthcare professionals can make informed decisions regarding dosage, route of administration, and dosing schedule. Bullet points Clinical Significance of Plasma Drug Levels: ● ● ● ● ● ● Plasma drug levels can be monitored to regulate drug responses Plasma drug levels can be adjusted by changing dose size, dose timing, or both Regulating plasma drug levels is based on the assumption that drug concentrations in the blood reflect concentrations at sites of action Age and renal function can affect drug excretion Infants have limited capacity to excrete drugs until their kidneys are fully developed In old age, renal function often declines, resulting in decreased renal excretion of drugs Nonrenal Routes of Drug Excretion: ● ● ● ● ● In most cases, nonrenal excretion of drugs has minimal clinical significance Nonetheless, nonrenal excretion can have important therapeutic and toxic consequences in certain situations Breast milk can expose nursing infants to drugs taken by breastfeeding women The passage of drugs into breast milk depends on factors such as lipid solubility, ionization, protein binding, and membrane permeability Drugs that are lipid-soluble have ready access to breast milk, while polar, ionized, or protein-bound drugs cannot enter in significant amounts Dosing Objective ● Consult with prescriber to ensure medication won't harm baby Important Plasma Drug Levels ● ● Minimum effective concentration (MEC) Toxic concentration Other Nonrenal Routes of Excretion ● ● ● ● Bile is an important route for excretion of certain drugs Bile can undergo reabsorption, known as enterohepatic recirculation Lungs excrete volatile anesthetics Small amounts of drugs can appear in sweat and saliva, but have little significance Therapeutic Range ● ● ● Range of plasma drug levels between MEC and toxic concentration Enough drug present for therapeutic effect, but not enough for toxicity Objective is maintaining drug levels within therapeutic range Time Course of Drug Responses ● Four pharmacokinetic processes determine time course: absorption, distribution, metabolism, and excretion Drug Half-Life ● ● Half-life is the time required for amount of drug in the body to decrease by 50% Some drugs have extremely short half-lives, while others exceed 1 week Note: ● Additional text was cut off. Please provide complete text for a more comprehensive summary. Understanding half-life and therapeutic range ● ● ● Drugs with a wide therapeutic range can be administered safely with relative ease The half-life of a drug determines how much of the drug is lost from the body over time Drugs with a narrow therapeutic range are more dangerous and require precise dosing to avoid toxicity Importance of therapeutic range in patient care ● ● Drugs with a narrow therapeutic range may require intervention for drug-related complications Nurses need to monitor patients taking drugs with a narrow therapeutic range for signs and symptoms of toxicity Drug accumulation with repeated doses ● ● ● ● When a patient takes repeated doses of a drug, the drug builds up in the body until a plateau (steady level) is reached The rate of accumulation depends on factors like absorption, metabolism, and excretion Plateau drug levels are necessary to maintain therapeutic responses Once drug levels fall below the minimum effective concentration (MEC), benefits of the drug cease