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CALCULATION WORKSHEET FOR WEIGHT
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AbbreviationsMeaningComments
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IBW Ideal Body WeightNot scientifically accurate but more commonly used
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LBWLean Body WeightRefers to the weight of all 'non-fat' body components including muscle and organs, useful for guiding dosing in obesity, but less commonly used due to its complexity
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ABW or TBW Actual Body Weight,
Total Body Weight
(same meaning)
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AdjBWAdjusted Body WeightUsed in obese patients especially when ABW is ≥ 20% of IBW
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Rule of thumb:
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If ABW < IBW, use ABW as the dosing weight
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Obese patients are those with BMI ≥ 30 or ABW is ≥ 20% of IBW
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The following reference is for ADULT PATIENTS only.
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DrugDosing Weight in Normal PatientsDosing Weight in ObesityRemarks
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Amikacin/GentamicinIBWAdjBW = IBW + (0.4 x (ABW - IBW))
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VancomycinABWAdjBW = IBW + (0.4 x (ABW - IBW))
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PhenytoinIBWFor initial loading dose:
Dosing Weight = IBW + 1.33 (ABW - IBW)

For subseqent load/MD:
Dosing Weight = IBW + 0.4 (ABW - IBW)
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Valproic acidIBWIBWClearance correlate better with IBW than ABW in obese patient
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CarbamazepineABWABWDistributes into all tissues
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Phenobarbitone
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DigoxinIBWIBW
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TheophyllineIBWIBWDistributes poorly into body fat
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Lithium
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1) Ideal Body Weight
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Patient's height =150cm
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For male:
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IBW =
50 kg + [0.91 x (Height - 152.4)]
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=48kg
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For female:
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IBW =
45.5 kg + [0.91 x (Height - 152.4)]
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=43kg
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2) Adjusted Body Weight
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IBW =73kg
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Actual BW =93kg
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AdjBW=IBW + 0.4 (ABW - IBW)
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=81kg
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