CG-CrCL Weight Selection

Weight selection for use in the CG-CrCL equation is an essential aspect of clinical pharmacokinetics and renal function estimation. The table below illustrates a suggested method for appropriately estimating renal function in individuals of all body sizes utilizing the CG-CrCL equation:

$$ \frac{(140-\mathrm{age})\times \mathrm{wt}}{72 \times \mathrm{SCr}}\times 0.85 \text{ (if female)} $$

† Across normal adult human heights, $$ 1.3 \times \mathrm{IBW} \equiv \mathrm{BMI} \approx 25 \text{–} 26 $$

‡ The use of LBW vs. Adj. Weight in this situation is debatable, but consideration of clinical scenario is imperative as neither weight produces highly reliable estimates of CrCL

CG-CrCL Estimation in Individuals with Amputation

To calculate the necessary weights for CrCL, the following information is needed

1. Patient’s current weight
2. Patient’s pre-amputation adult height (if amputation would have caused reduction in measured height, i.e. bilateral BKA’s)
3. Location of all amputations the patient has undergone

This calculator from clincalc.com may be useful. This calculator is utilizing the following data to compute values:

Calculations

IBWpre is calculated as normal using the patient’s pre-amputation height

$$ \mathrm{IBW}\mathrm{post} = \mathrm{IBW}\mathrm{pre} \times (1-\mathrm{EBWL}) $$

$$ \text{Adj. Wt} = \mathrm{IBW}\mathrm{post} + 0.4\left( \mathrm{Wt} - \mathrm{IBW}\mathrm{post} \right) $$

Estimation of Chronic Renal Function

Estimation of chronic renal function can be most accurately be computed using the CKD-EPI equation, a copy of which can be found here on mdcalc.com