Farmacocintica

1
Distribution. Where do drugs go?
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2
Volume of distribution

• Apparent and hypothetical volume in which the
  drug is dispersed.

• Why is it relevant?
• To calculate the loading dose of a drug

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3
Volume of distribution

• Relative size of various distribution volumes
  within a 70-kg individual
• Plasma 4 liters.
• Interstitial volume 10 liters.
• Intracelullar volume 28 liters

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4
Plasma compartment

• Vd around 5 L.
• Very high molecular weight drugs, ordrugs that
  bind to plasma proteins excesively
• Example heparin 4L (3-5)

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5
Extracellular fluid

• Vd between 4 and 14 L.
• Drugs that have a low molecular weight but are
  hydrophilic.
• Example
• Atracuronium 11 L (8-15)

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6
Vd equal or higher than total body water

• Diffusion to intracelullar fluid . Vd equal to
  total body water.
• Ethanol 38 L (34-41)
• Alfentanyl 56 L (35-77)
• Drug that binds strongly to tissues. Vd higher
  than total body water.
• Fentanyl 280 L
• Propofol 560 L
• Digoxin385 L