Enteric-Coated Preparations

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 Tablets ● ● Mixture of drug with binders and fillers compressed together Differences in tablet composition between manufacturers can cause variations in disintegration, dissolution, and bioavailability Enteric-Coated Preparations ● ● ● Drugs covered with material that dissolves in the intestine but not the stomach Used to protect drugs from stomach acid and pepsin, and to protect the stomach from drugs that cause gastric discomfort Absorption can be more variable than with standard tablets, affected by gastric emptying time Disadvantages of oral administration ● ● Inactivation: Oral administration can lead to inactivation of certain drugs by stomach acid, digestive enzymes, or liver metabolism Patient requirements: Requires a conscious, cooperative patient; cannot be administered to comatose individuals ● Local irritation: Some oral preparations can cause discomfort, nausea, and vomiting due to irritation of the gastrointestinal tract Administration methods ● ● Oral administration is generally preferred due to its ease, convenience, and safety Parenteral administration may be superior in certain situations Sustained-release preparations ● ● ● Sustained-release formulations release the drug steadily throughout the day Advantages include a reduction in the number of daily doses and steady drug levels Disadvantages include high cost and potential for variable absorption Distribution of drugs in the body ● ● ● ● Drugs are carried by the blood to tissues and organs The rate of delivery to a specific tissue is determined by blood flow to that tissue Most tissues have sufficient blood flow for drug distribution Low regional blood flow can affect drug distribution in abscesses and tumors Capillary beds and drug movement ● ● In capillary beds, gaps between cells allow drugs to pass freely between the bloodstream and tissues Lipid-soluble compounds can also pass directly through the cells of the capillary wall Additional routes of administration ● Drugs can be administered topically for local therapy ● ● Some drugs are formulated for transdermal absorption into the systemic circulation Inhalation is used for local effects in the lungs Blood-brain barrier ● ● The blood-brain barrier refers to the unique anatomy of capillaries in the central nervous system (CNS) Tight junctions between cells restrict drug movement into the CNS Role of Blood-Brain Barrier (BBB) in Drug Distribution ● ● ● ● ● The BBB prevents most inhalational agents, such as volatile anesthetics and oxygen, from accessing the CNS Rectal and vaginal suppositories may be used for local effects, as they prevent drug passage through the BBB Only lipid soluble drugs or drugs with a transport system can cross the BBB to reach the brain The BBB can be an obstacle to treating CNS disorders as it impedes drug access to the brain Recent evidence suggests that the BBB has a protective component called PGP, which pumps drugs out of cells Drug Distribution ● ● ● Distribution is the movement of a drug from the blood to tissues and cells Factors influencing drug distribution include blood flow to tissues, the ability of a drug to exit the vascular system, and the ability of a drug to enter cells The presence of the BBB can hinder drug distribution to the brain, limiting therapy for CNS disorders Placental Drug Transfer ● ● ● ● ● The placental membranes separate the maternal and fetal circulations These membranes do not constitute an absolute barrier to drug passage Factors determining drug movement across the placenta are similar to those for other membranes Lipid-soluble drugs can readily cross the placental membranes, while ions and polar molecules are prevented from reaching the fetal blood Drug binding to albumin is reversible, and only a percentage of the drug molecules will be bound at any moment