University:
York University
Course:
CHEM 2550 | Pharmacology for Health Sciences
Academic year:

2022
Views:

442

Pages:

2
Author:

Niklas

Chp 3 Pharmacokinetics Phases: DRUG → Absorption → Distribution → Metabolism → Excretes Pharmacokinetics: What body does to the drug. Kinetics: Movement. Study of drugs + movement through the body. Bioavailability: Amount of drug that reaches bloodstream Factors affecting Absorption Circulation: Blood to GI tract. Pain, stress, exercise: Shunts blood away from gut → affected muscles. Food: ↑ Time for drug to reach intestines (rate of absorption) pH: Needs pH to breakdown drugs into absorbable form, ↑ pH inhibits absorption of drugs In order for body to use (absorb) oral drugs they must be broken down into smaller particles (disintegration) + dissolved (dissolution) First Pass Effect: Affects absorption/bioavailability of ORAL meds. The amount of drug inactivated BEFORE it reaches systemic circulation. DRUG (PO) → Small Intestine → Portal Vein → Liver → Body (*First pass) Following oral admin, drug is absorbed thru intestinal wall, enters hepatic portal system, carried to liver via portal vein where some of drug is inactivated before reaches circulation. Ex: IV vs. PO 100% Available, 20% Inactivated GI Motility: Delays absorption Factors affecting Distribution Drug interaction: plasma proteins - "protein binding" if drug is tightly bound to plasma proteins, it won't be alone to reach target cells *Tight binding prevents drug delivery Unbound portion is the "free drug" that reaches tissues. Conversely low plasma protein = ↑ free drug = ↑ risk for toxicity. Anatomical barrier: a. Blood-brain barrier b. Placental barrier Factors affecting Metabolism Half life: Amount of time taken for amount of drug in body to be reduced by half. Steady state: Achieved when plasma concentration of drug builds up to a level that is therapeutically effective. Time it takes is about 5 half lives. How can we get drugs to a steady state sooner? LOADING DOSE Loading Dose: large initial dose, followed by maintenance doses. Factors affecting excretion (elimination) Kidney/liver function - If inadequate, drug sticks around in body longer. • Kidney function is measured by CrCl 10-28 ~10/06-12) - Liver function measured by LFTs (ALT/AST)