Drug Movement and Processes

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 Drug Movement and Processes ● ● ● ● Absorption: The drug's movement from its site of administration into the blood Distribution: The drug's movement from the blood to the interstitial space of tissues and from there into cells Metabolism: The enzymatically mediated alteration of drug structure Excretion: The movement of drugs and their metabolites out of the body Factors Affecting Drug Absorption ● ● ● Three ways to cross a cell membrane: passive diffusion, facilitated diffusion, active transport Characteristics of commonly used routes of administration: oral, intravenous, subcutaneous, etc. Factors affecting drug absorption Application of Pharmacokinetics in Therapeutics ● ● ● Maximizing beneficial effects and minimizing harm in drug therapy Importance of drug concentration at the site of action for desired responses Selection of the most appropriate route, dosage, and dosing schedule Role of Nurses in Applying Pharmacokinetics ● ● ● Using knowledge of pharmacokinetics in clinical practice to avoid medication errors Questioning or challenging prescribers regarding dosage, route, or schedule of administration Understanding pharmacokinetics to support logical rationale in altering a prescriber's decision Importance and Benefits of Knowledge of Pharmacokinetics ● ● ● Decreasing stress and increasing intellectual and professional satisfaction in nursing practice Demystifying drug therapy and increasing understanding of drug movement throughout the body Four basic pharmacokinetic processes: absorption, distribution, metabolism, and excretion Methods of drug passage through cell membranes ● ● ● Passage through channels or pores Passage with the aid of a transport system Direct penetration of the membrane itself Channels and Pores ● ● ● Very few drugs cross membranes via channels or pores Channels in membranes are extremely small and specific for certain molecules Only the smallest compounds can pass through these channels Membrane Structure ● Biologic membranes are composed of layers of individual cells Transport Systems ● ● ● Transport systems are carriers that move drugs from one side of the membrane to the other Some transport systems require energy, others do not Transport systems are selective and will not carry any drug Drug penetration through membranes ● ● ● ● ● Some molecules are not lipid soluble and cannot penetrate membranes This group includes polar molecules and ions Transport systems are necessary for the transit of certain drugs Polar molecules have an uneven distribution of electrical charge Polar molecules are soluble in polar solvents like water P-Glycoprotein (PGP) ● ● ● ● ● ● ● PGP is a transporter protein that pumps drugs out of cells It is present in various cells, including liver, kidney, placenta, intestine, and brain capillaries In the liver, PGP transports drugs into bile for elimination In the kidney, it pumps drugs into urine for excretion In the placenta, it transports drugs back into maternal blood to reduce fetal exposure In intestine, it transports drugs into the intestinal lumen to reduce absorption into the blood In brain capillaries, it pumps drugs into the blood to limit drug access to the brain