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Module 9 Notes.docx

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Department
Pharmacology
Course
Pharmacology 2060A/B
Professor
Angela Nissen
Semester
Spring

Description
Module 9 Pharmacodynamics: Therapeutic Index 9.1 Interpatient Variability in Response • Responses to medications vary between patients • Due to this, every patient’s response must be evaluated to ensure an adequate therapeutic response • Influenced by genetics, disease state, and environment • Determining Interpatient Variability • Clinical Trials – important first step  • Phase II clinical trials establish dose response information over range of doses o To determine interpatient variability, first set an endpoint  Ex. If talking about analgesic drug, endpoint would be pain relief o Can evaluate number of patients that experience pain relief from each dose of drug o Data plotted on frequency distribution curve  Average effective dose (ED50) is at peak  The ED50 is the dose required to produce a response in 50% of the population • Often used as the initial dose for therapy • Dosing Complications o If all patients given ED50 as starting dose, some patients will have more drug than they need and  others will not as seen in graph o ED50 is starting point – many patients will need dose adjustments to optimize efficacy and  minimize adverse events o When is it okay to use ED50 as starting dose?  When drug has wide therapeutic range • Decreased risk of adverse events o How do we dose drugs that have narrow therapeutic range?  Should have dose titrated • Start low and increase slowly until desired response is achieved o most importantly, adjust dosing based on patient’s response rather than simply using dosing  reference • Toxic and Lethal Doses o Responses can include toxicity or even death due to drug treatment o These tests carried out in experimental animals o Acute (Short term) and chronic (6 months­2 years) animal tesing is carried out to determine the  doses that produce toxicity or death in multiple animal species o TD50 – average toxic dose, 50% of animals experience drug toxicity o LD50 – average lethal dose, 50% of animals die o Both typically expressed in mg drug/kg body weight 9.2 Therapeutic Index • Indicator of drugs safety • Calculated by determining ration of TD50 or LD50 to ED50 TI=TD50/ED50 or  TI=LD50/ED50 • Drugs with high TI are considered safe • Low TI unsafe • Drugs that are safe have a large space in between the dose that produces a therapeutic response and the  dose that produces toxic/lethal response 9.3 Factors Affecting Interpatient Variation in Response 1. Body weight and composition 2. Genetics 3. Gender 4. Race 5. Kidney disease 6. Liver disease 7. Environment  1. Body Weight and composition • Higher concentration in body gives greater response • Same dose to two guys  ▯h
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