Elimination Flashcards

1
Q

Elimination

A

Irreversible elimination of drug from body by ALL routes.

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2
Q

Elimination Routes (2)

A
  1. Metabolism

2. Excretion

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3
Q

Metabolism

A
  • Chemically converting a drug to a metabolite
  • AKA biotransformation
  • Usually enzymatic which are usually found in liver
  • Other tissues also have biotransformative enzymes (lungs, skin, kidneys, etc.)
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4
Q

Excretion

A
  • Removal of intact drugs
  • Done primarily by kidney
  • Other pathways include excretion into bile, sweat, milk, or other body fluids
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5
Q

First Order Elimination Rate Constant (K)

A
  • Proportionality constant relating rate and amount of drug eliminated
  • Unit = time^(-1)
  • Least-squared regression line is most accurate measurement
  • Liver & kidney are the most important elimination organs
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6
Q

K Equation

A

K = ke + km

t1/2 = 0.693 / K

(fe * K = ke, same for fm/km)

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7
Q

Fraction excreted (fe)

A

Percent of drug excreted uncharged in urine

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8
Q

Fraction metabolized (fm)

A

Percent of drug metabolized by body (ALL metabolites)

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9
Q

Clearance

A
  • Proportionality constant describing relationship between a drug’s rate of elimination at a given time and its corresponding fluid
  • Measure of elimination without mechanism or process
  • Considers entire body as a drug elimination system from which many processes occur
  • Refers to Volume of Fluid Cleared / Unit Time
  • Rate of removal varies as drug declines but clearance will be a constant since body fluid is a constant
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10
Q

Clt equation

A

Clt = Clr + Clnr

Clt = Total Clearance
Clr = Renal Clearance
Clnr = Non-renal Clearance
Cl = VK
Cl = FDose / AUC ** Preferred method since doesn't depend on half lives or V**
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11
Q

Physiological Approach to Clearance

A
  • Models based on drug clearance through individual organs/tissue groups
  • Based on mass balance concept
  • Extraction ratio utilized
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12
Q

Extraction Ratio (E)

A

E = (Ca - Cv) / Ca

Ca = arterial drug concentration
Cv = venous drug concentration
-Quantifies the organ efficiency with elimination and fixed flow
-Ranges from 0-100%
-E = 0 (none removed), E < 30% (not efficiently removed), E > 70% (efficiently removed)

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13
Q

Clearance + Elimination Ratio

A

-For any organ, clearance may be defined as the fraction of blood volume containing drug that flows through an organ is elimination per unit time

Cl = QE

Q = Organ blood flow
E = Elimination ratio
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