objectives Learn the 4 phases of pharmacokinetics and factors that influence

Objectives learn the 4 phases of pharmacokinetics and

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objectives Learn the 4 phases of pharmacokinetics and factors that influence them Understand the impact that hepatic enzymes play in metabolism of drugs Understand the first-pass effect and the impact it has on drug bioavailability
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Pharmacokinetics “pharmaco”- medicine “kinetics”- movement or motion Drugs work on a cellular level- need to reach their “Target Cells” to be effective Many obstacles are encountered during this trip Plasma membranes of mucosal cells of GI tract Plasma membranes of capillary endothelial cells Interstitial fluid
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Figure 2.1 A drug’s bioavailability will depend on the dosage form and how much will actually reach the target location
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Passage of drugs through Plasma Membranes 2 processes to cross body membranes Active transport movement of a chemical against a concentration or electrochemical gradient Diffusion or passive transport movement from higher concentration to lower concentration
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Four categories of pharmacokinetics 1. Absorption 2. Distribution 3. Metabolism 4. Excretion
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Figure 4.1 The four processes of pharmacokinetics: absorption, distribution, metabolism, and excretion
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Absorption: Refers to drug moving from site of administration, across body membranes to circulating fluids Absorption is the primary factor determining the length of time it takes a drug to produce its effect Absorption is influenced by the drug formulation, drug dose, speed of digestive motility, digestive enzymes and blood flow to the site
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Factors affecting absorption Route of administration Drug formulation Drug dosage Digestive motility Digestive tract enzymes Blood flow at administration site Degree of ionization of drug In acid of stomach, aspirin is nonionized and easily absorbed by bloodstream. In alkaline of small intestine, aspirin is ionized and less likely to be absorbed. pH of surrounding environment Drug-drug/drug-food interactions Dietary supplement/herbal product–drug interactions
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Distribution: Involves the transport of pharmacologic agents throughout the body BLOOD FLOW to the body tissues is a major factor in distribution Lipid soluble agents= better distribution Tissue affinity for drugs Protein binding capability Protein binding competition Blood-brain barrier/fetal-placental barrier
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Drugs Bind with Plasma Proteins Many drug molecules form drug– protein complexes —binding reversibly to plasma proteins—and thus never reach target cells. Cannot cross capillary membranes Drug not distributed to body tissues
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Figure 4.3 Plasma protein binding and drug availability: (a) drug exists in a free state or bound to plasma protein; (b) drug–protein complexes are too large to cross membranes
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Distribution of Medications Drugs and other chemicals compete for plasma protein–binding sites.
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