NURS 8024 (Medicine) Advanced
Pharmacology Definitions and Concepts
Week 1 Summary A+ GRADED.
Competition for Plasma Protein Binding: Class II (minority of drugs)
✔✔-High dose/capacity ratio
-Amount of drug > albumin binding capacity
-High proportion of drug in "free" state = not protein bound
Clinical Implications of Plasma Protein Binding
✔✔Drug displacement from albumin substantial
source of drug interactions.....
• Class I drug - warfarin
• Highly protein bound - small fraction of free drug in plasma
↓
• Class II drug given - sulfa
• Displaces warfarin from albumin
• Rapid rise in free drug concentration
• Increased therapeutic effect- toxic effect
Drug Displacement and Vd
✔✔--Dependent on Vd and therapeutic index of drug
--Large Vd verses small Vd (drug is less around)
,What is the therapeutic index (TI)?
✔✔Ratio of a drug's toxic level to the level that provides therapeutic
benefits--Measure of drug safety--Safer Drug has a higher TI
--If the Therapeutic Index is narrow--small increase in drug
concentration can have a substantial clinical impact Ex: Digoxin (the
closer the ratio is to 1 the less safe the drug)
What are the components of calculation of TI? Toxic dose for 50 % of
people divided by the effective does for 50% of people). Therapeutic Dose
Divided by the Lethal Dose : TI = TD50 Divided by ED50
Drug Metabolism-First Order Kinetics (most drugs)
✔✔--Metabolic transformation of drugs by enzymes
--Rate of drug metabolism is directly proportional to the concentration of
free drug--so CONSTANT FRACTION of drug per unit of time is
eliminated
--Linear elimination pattern: reflected by 1/2 life of the drug
--Each half life cuts the drug concentration by 50%
At 2 Half lives= drug has been 75% removed
At 5 Half lives= drug is essentially removed from the body
--has a CURVED ELIMINATION LINE ON GRAPH
Drug Metabolism -- Zero Order Kinetics (minority of drugs)
✔✔ASA, Ethanol, Phenytoin
Rate of metabolism is constant OVER TIME---therefore a CONSTANT
AMOUNT of drug is metabolized per unit of TIME
--HAS A STRAIGHT ELIMINATION LINE ON GRAPH
, Process of Drug Metabolism
✔✔Phase 1 and Phase 2
Phase 1: increase polarity and water solubility of the drug (oxidation and
hydrolysis)
Phase 2: Involves conjugation: Increase solubility and facilitates secretion
of the metabolite from the body
--Some drugs undergo phase 1 and 2 metabolism
--Some drugs only undergo one of the phases--dependent on the
chemical nature of the drug
Kidneys filter more water soluble drugs; Liver filters more lipid soluble
drugs
Phase 1 drug metabolism
✔✔Oxidation, reduction, hydrolysis
https://www.nottingham.ac.uk/nmp/sonet/rlos/bioproc/liverdrug/pag
e_two.html
Phase 2 drug metabolism
✔✔Involves Conjugation (the attachment of an ionized group to the
drug)
--increases solubility, facilitates excretion from the body
https://www.nottingham.ac.uk/nmp/sonet/rlos/bioproc/liverdrug/pag
e_two.html
Lipid Soluble drug and phase 2 metabolism
✔✔Phase 2 happens first then phase 1 for a lipid soluble drug--it will be
eliminated after phase 1
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