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Pharmacology
Enzyme Kinetics and Pharmacokinetics equations
9
Art History
1st Grade
05/07/2012

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Term
Define Km
Definition
Value of [substrate] which equals 1/2 of Vmax

Determines the enzyme affinity toward substrate:
Smaller Km (small substrate) means HIGHER affinity because only a small substrate concentration needed to achieve 1/2Vmax

Larger Km (large substrate) means LOWER affinity because it takes a large amount of substrate to achieve 1/2Vmax
Term
Define Vmax
Definition
The speed of the reaction at which all the enzymes are occupied with substrate (supersaturated).
Term
Volume of Distribution
Definition
Vd (volume drug was dissolved in) = Amount of drug /Plasma concentration of drug

Rearranged from simply:
Plasma concentration of drug = Amount of drug/Volume that drug was dissolved in
Term
Clearance
Definition
CL = (0.7 x Vd)/T-halflife

Rearranged to find halflife:
T-halflife = (0.7 x Vd)/CL
Term
Loading Dose
Definition
Loading dose = Cp (target concentration)/ Vd
Term
Maintenance Dose
Definition
Maintenance Dose = Cp(target concentration)/CL

Replace what was lost (Clearance amount)
Term
Competitive Inhibitor effects on Km and Vmax
Definition
Km increases (needs more substrate to overcome the inhibitor)

Vmax remains unchanged (inhibitor did not do anything to effect the quality of the enzyme)
Term
Non-Competitive (irreversible) inhibitor effects on Km and Vmax
Definition
Km remains the same

Vmax Decreases (allosteric binding of inhibitor causes conformational change of enzyme. Quality of reaction is effected)
Term
Therapeutic Index
Definition
Lethal Dose 50/Therapeutic Dose50

The larger the therapeutic index, the safer the drug is. (higher LD50 and lower TD50)
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