Wait, Which Weight?: Weight-Based Dose Adjustments of Medications Commonly Used in the ED

Below is a table of common medications used in the emergency department that require dose adjustments based on the weight in the obese patient:

Important notes:

  • ABW = actual body weight (kg)
  • IBW = ideal body weight (kg)
    • Calculation:
      • Males: 50 + (2.3 x number of inches over height of 60″)
      • Females: 45.5 + (2.3 x number of inches over height of 60″)
  • AdjBW = adjusted body weight (kg)
    • To be used if ABW is at least 120% above IBW
    • Calculation:
      • IBW + 0.4 (ABW – IBW)
  • *Phenytoin:
    • Loading dose: AdjBW = IBW + 1.33 (ABW – IBW)
      • Maximum loading dose: 2 g
    • A large correction factor of 1.33 due to an expanded volume of distribution of phenytoin in the obese patient.

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