Updated: 11/2/2018

Drug Excretion

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Overview
  • Cell membranes 
    • bilayer of amphipathic lipids with the hydrophobic chains pointing inwards and the hydrophilic heads pointing outwards
    • like dissolves like, thus charged (ionized) molecules will have a difficult time crossing this bilayer with uncharged (non-ionized) molecules crossing more easily
  • Urine pH
    • tends to be acidic but pH ranges from 4.6 - 8.0
Weak acids and bases
  • Weak acids
    • RCOOH (lipid soluble) ↔ RCOO- (trapped) + H+
    • in basic environments, weak acids become charged by deprotonation
      • will become trapped on side of the lipid bilayer that is basic
    • to treat overdose of weak acids, administer bicarbonate (weak base)
    • examples of drugs that are weak acids
      • aspirin
      • phenobarbital 
      • methotrexate
  • Weak bases
    • RNH3+ (trapped) ↔ RNH2 (lipid soluble) + H+
    • in acidic environments, weak bases become charged by protonation
      • will become trapped on the side of the lipid bilayer that is acidic
    • to treat overdose of weak bases, administer ammonium chloride (weak acid)
    • example of a drug that is a weak base
      • amphetamines/methamphetamines
      • TCAs
        • TCA overdose treated with sodium bicarbonate

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(M1.PH.17.4699) A group of researchers wish to develop a clinical trial assessing the efficacy of a specific medication on the urinary excretion of amphetamines in intoxicated patients. They recruit 50 patients for the treatment arm and 50 patients for the control arm of the study. Demographics are fairly balanced between the two groups. The primary end points include (1) time to recovery of mental status, (2) baseline heart rate, (3) urinary pH, and (4) specific gravity. Which medication should they use in order to achieve a statistically significant result positively favoring the intervention?

QID: 108317
1

Potassium citrate

11%

(18/171)

2

Ascorbic acid

29%

(49/171)

3

Aluminum hydroxide

6%

(11/171)

4

Sodium bicarbonate

39%

(67/171)

5

Tap water

11%

(18/171)

M 3 D

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