• Physical and Chemical Characteristics of the Drug
  • Molecular weight (<500)
  • Lipid solubility
  • Nonionized vs. ionized
• Concentration Gradient
  • Dose administered
  • Timing of IV administration relative to uterine contraction
  • Use of vasoconstrictors
• Hemodynamic Factors
  • Aortocaval compression
  • Hypotension from regional blockade

IV = intravenous.