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Pharmacokinetics Lecture 2 CL, Fe, AUC

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alchemist04's version from 2016-07-19 02:07

Section

Question Answer
VdTotal Volume distribution
Vd formula (1) =(1) Vp + (Vt) (fu/fut)
Vd formula (2) =(2) Amount of drug in the body / plasma conc of drug
CLr =Fe * CL or CLt
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Question Answer
Fe isfraction of IV bolus doses excreted unchanged
Fe always range from0 - 1
Low Fe meansthe drug passed through metabolism in the liver and has minimum or minor drug elimination via kidney (renal)
High Fe meansThe drug does not pass through liver metabolism and majority are excreted via kidney (renal)
Fe formula isTotal amount of drug excreted in urine (mg) / Total amount of drug administered (mg) or total dose given.
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Question Answer
When CLr = Fu * GFR that meansdrug is primarily excreted by filtration @ Bowsman Capsule(drug is made up of small non-protein molecules)
When CLr > Fu * GFR that meansDrug is actively secreted in Proximal Tubule and the drug is ionic (base or acidic drugs)
When CLr < Fu * GFR that meansDrug undergoes passive tubular reabsorption at distal tubule and the drug is unionized (lipid drugs)
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Question Answer
CLh isHepatic Clearance (i.e. drug metabolism, 1st pass)
CLh formula (1)(1) CLh = CLt - CLr or CLt (1-Fe)
CL(organ) is used in hepatic measurement, What is the formula (2)(2) CL organ = Q * [(Cin - Cout)/Cin]
CL(organ) formular (3)(3) CL(organ) = Q * ER
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Question Answer
K =Elimination Rate constant. Same as elimination from the plasma. Elimination from the plasma is the same as 1st order = hepatic clearance/metabolism
Kel =is represent 1st Order, not the same as learance and changes with concentration while half-life (t 1/2) half life is unchanged when concentration changes.
K formula is CL / Vd
When drug concentration is increased from 20 mg/L to 40 mg/L, what would happen to the drug half life that is under 1st kinetic order?The half life remain the same.
When a drug concentration is increased from 20 mg/L to 40 mg/L, what would happen to the drug (1) Rate of elimination (2) Clearance and (3) Rate of elimination constant (Kel)?(1) Rate of elimination increases (2) Clearance remain the same (3) Rate of elimination constance increases proportionally
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Question Answer
t(1/2) isHalf life
t (1/2) formula is (1)(1) (0.693/K)
T(1/2) formula is (2)(2) (0.693 * Vd) / CL or CLt
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Question Answer
AUCArea Under the Curve
AUC formula isDose/CL [(mg)(hr)/(L)]
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Question Answer
What are the primary Pharmacokinetics parameters?(1) Vd (2) CL
What are the secondary Pharmacokinetics parameters?(1) Half-life (2) Kel. Why? because they rely on CL and Vd (the primary pharmacokinetics)
What is/are the tertiary Pharmacokinetics parameter(s)?AUC. Why? Because it depends on CL and Vd (the primary pharmacokinetics) and drug doses.
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