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#Lean body weight '''(LBW)'''= Difference between TBW and fat mass<br>  
#Lean body weight '''(LBW)'''= Difference between TBW and fat mass<br>  
##Technically best weight scalar for drug administration but difficult to accurately measure
##Technically best weight scalar for drug administration but difficult to accurately measure
#Adjusted body weight (ABW) = Scalar derived from aminoglycoside pharmacokinetics (PK) in obesity


== Estimating Patient Weight  ==
== Estimating Patient Weight  ==
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###IBW (female) in kg = 45kg + 2.3kg for each in. over 5ft  
###IBW (female) in kg = 45kg + 2.3kg for each in. over 5ft  
#'''Estimated LBW''' = 1.3 x IBW  
#'''Estimated LBW''' = 1.3 x IBW  
#Others:  
#'''Estimated ABW''' = IBW + [C x(TBW-IBW)]
##C = correction factor ususally 0.2 to 0.4
#Apps/Online resources:  
##Epocrates has IBW calculator  
##Epocrates has IBW calculator  
##Http://www.medcalc.com/body.html
##Http://www.medcalc.com/body.html
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| Dose by IBW
| Dose by IBW
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|  
| Heparin
|  
| Same as non-obese pt (80U/kg followed by 18U/kg/h using TBW)
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| Vancomycin
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| 30 mg/kg TBW (then follow serum levels)
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| Aminoglycosides
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| Dose by ABW (C= 0.4; then follow serum levels)
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|  
| Beta-lactams
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| No good data, may consider doubling dose
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| Carbapenems
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| No empiric change recommended
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| Antifungals
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| No empiric change recommended; use LBW when dosing weight-based agents
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Revisión del 06:43 19 ago 2013

Definitions

  1. Overweight = BMI 25-29
  2. Obesity = BMI 30-39
  3. Morbid obesity = BMI 40-49
  4. Super obesity = BMI >50

Dosing Scalars

  1. Total body weight (TBW)= Actual weight
    1. May result in over dosing
  2. Ideal body weight (IBW)= Calc. based on height & weight
    1. May result in under dosing
  3. Lean body weight (LBW)= Difference between TBW and fat mass
    1. Technically best weight scalar for drug administration but difficult to accurately measure
  4. Adjusted body weight (ABW) = Scalar derived from aminoglycoside pharmacokinetics (PK) in obesity

Estimating Patient Weight

Multiple formulas to estimate weight, below are most common:

  1. Estimated male TBW = 93.2 + 3.29[arm circumference (cm)] + 0.43[height (cm)]
  2. Estimated female TBW = 64.6 + 2.15[arm circumference (cm)] + 0.54[height (cm)]
  3. Estimated male IBW in kg = height in cm - 100
    1. More accurate IBW estimate:
      1. IBW (male) in kg = 50kg + 2.3kg for each in. over 5ft
  4. Estimated female IBW in kg = height in cm - 105
    1. More accurate IBW estimate:
      1. IBW (female) in kg = 45kg + 2.3kg for each in. over 5ft
  5. Estimated LBW = 1.3 x IBW
  6. Estimated ABW = IBW + [C x(TBW-IBW)]
    1. C = correction factor ususally 0.2 to 0.4
  7. Apps/Online resources:
    1. Epocrates has IBW calculator
    2. Http://www.medcalc.com/body.html

Medication Adjustments in Obesity

Obesity alters hepatic/renal clearance and volume of distribution (Vd) of many drugs.

Medication Adjustment in Obesity
Medication Dose Adjustment 
Morphine Dose by IBW
Fentanyl Dose by LBW; Alternative initial dose TBW, subsequent dose by IBW (risk over dose when use TBW)
Midazolam Initial dose TBW, subsequent dose by IBW
Propofol  Dose by LBW
Etomidate Dose by LBW
Succinylcholine Dose by TBW @ 1mg/kg
Rocuronium Dose by IBW
Heparin Same as non-obese pt (80U/kg followed by 18U/kg/h using TBW)
Vancomycin 30 mg/kg TBW (then follow serum levels)
Aminoglycosides Dose by ABW (C= 0.4; then follow serum levels)
Beta-lactams No good data, may consider doubling dose
Carbapenems No empiric change recommended
Antifungals No empiric change recommended; use LBW when dosing weight-based agents


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