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Lecture 6+7 - Pharmacology Basics

Rate of elimina3on is independent of drug

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Unformatted text preview: alcohol breath •  Breast milk acidic  ­ ­ ­> ion traps alkaloids alcohol: same concentra3on as blood an3bio3cs •  Also bile, skin, saliva ~~ Metabolism and Elimina&on (cont.) •  Half ­lives and Kine3cs –  Half ­life: •  Plasma half ­life: Time it takes for plasma concentra3on of a drug to drop to 50% of ini3al level. •  Whole body half ­life: Time it takes to eliminate half of the body content of a drug. –  Factors affec3ng half ­life •  age •  renal excre3on •  liver metabolism •  protein binding First order kine&cs A constant frac&on of drug is eliminated per unit of 3me. When drug concentra3on is high, rate of disappearance is high. Zero order kine&cs Rate of elimina3on is constant. Rate of elimina3on is independent of drug concentra3on. Constant amount eliminated per unit of 3me. Example: Alcohol Comparison •  First Order Elimina3on –  [drug] decreases exponen3ally w/ 3me –  Rate of elimina3on is propor3onal to [drug] –  Plot of log [drug] or ln [drug] vs. 3me are linear –  t 1/2 is constant regardless of [drug] •  Zero Order Elimina3on –  [drug] decreases linearly with 3me –  Rate of elimina3on is constant –  Rate of elimina3on is independent of [drug] –  No true t 1/2 Drug Effec&veness •  Dose-response (DR) curve –  Depicts the relation between drug dose and magnitude of drug effect •  Drugs can have more than one effect •  Drugs vary in effectiveness –  Different sites of action –  Different affinities for receptors •  The effectiveness of a drug is considered relative to its safety (therapeutic index) ED50 = effec3ve dose in 50% of popula3on 100 % sub...
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