Below is a table of common medications used in the emergency department that require dose adjustments based on 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
  • Large correction factor of 1.33 due to expanded volume of distribution of phenytoin in the obese patient.