HLTH 471 & 671 (2022) - introduction to pharmacology, part 2

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University of Waterloo *

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471

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Health Science

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Oct 30, 2023

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pptx

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Principles of Pharmacology Winter, 2022 HLTH 471/671

Key Points 1) Psychopharmacology defined. 2) Pharmacokinetics. 3) Pharmacodynamics.

• Distribution - A drug rarely acts at its point of initial contact upon the body. - Movement of drug from point of administration to blood influenced by: 1) route of administration, which affects: - area of absorbing surface - metabolism - binding to food/inert substances 2) depot binding 3) selective barriers 4) transport across membranes - lipid solubility & ionisation Blood Concentration IV IM SC ? Time (h) Pharmacokinetics 6

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↓ [d rug] at site of action ↓ me tabolism by ? unexpected effects Pharmacokinetics 7  depot binding - drug binding can occur at sites wherein no biological effect is initiated - drug depots include plasma proteins (e.g., albumin), muscle, and fat - binding at depots is reversible - depots ↓ intensity, but ↑ du ? ration - major effects of depots (silent receptors):

 selective barriers (e.g., the blood-brain barrier; BBB) • BBB - selectively permeable barrier - limits access of water soluble and molecules - facilitated diffusion exists • tight junctions Specialised regions of brain endothelial cells that resistance to transport. Pharmacokinetics 8

 transport across membranes – lipid solubility Pharmacokinetics • Membrane permeability is often affected by 3 properties of a compound. - drugs with high lipid solubility move through membranes by passive diffusion along a co ? ncentration gradient 9

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e.g., aspirin  transport across membranes - ionisation • The extent to which a molecule dissociates into ions when placed in water. Pharmacokinetics Ionisation is influenced by: molecule pKa & solvent pH pH of aqueous sol’n in which compound is 50% ionised 10 Ionisation affects: ? lipid solubility