1. Evaluation of a novel method for determination of
Ideal Body Weight in patients undergoing HSCT
Lindsey Parker, Claire Gorry, Fionnuala King
Pharmacy Department, Saint James’s Hospital, Dublin, Ireland
FKing@stjames.ie
The consensus guidelines produced by the American
Society for Blood and Marrow Transplant (ASBMT) in
2014 highlight the lack of grade I/II level evidence for
dosing of conditioning regimens for obese and
overweight patients undergoing haematopoietic stem
cell transplantation (HSCT).
ASBMT recommend the use of an ideal body weight
(IBW) for the determination of dose of a number of commonly used
drugs including busulfan, carmustine, cyclophosphamide and
etoposide.
Traditionally the Devine formula (Devine 1974) has been used for
the calculation of IBW (IBWD). This formula calculates IBW which
corresponds to a BMI of 23 kg/m2
for men and 20.8 kg/m2
for
women. As therapeutic dose monitoring of doses used in
conditioning regimens is not available in Ireland, it is necessary that
we improve the empirical methods used to determine optimal
dosing for obese and overweight patients.
We analysed conditioning regimens from 150 HSCT
patients (2014-2015) and recorded patient
parameters, conditioning regimen, and doses received.
Based on the recorded parameters, we calculated
patient BMI, IBWD, and an ideal body weight
calculated from the BMI formula (IBWBMI):
24.9 × (Height in meters)2
= IBWBMI
A target BMI of 24.9 (the upper limit of normal) was used in the
equation for both males and females.
First, we compared the two IBW values (IBWD and IBWBMI), and
determined the percentage difference.
Then we examined the impact on dosing caused by using IBWBMI
versus IBWD to determine if there is a significant difference (> 5%).
IBWBMI versus IBWD
IBWBMI is on average 12% higher than
IBWD, across both genders and all
BMI values (Female: 17%, Male: 8%).
There was much larger variation seen
for females under 160cm (18-23%)
regardless of BMI (Graph 1).
Dosing implications
Using IBWBMI rather than IBWD in
dose calculations resulted in 10%
higher busulfan doses (4–17%), 7%
higher carmustine doses (3–12%),
and 12% higher cyclophosphamide
doses (7–23%) (Graph 2). Shorter
busulfan and cyclophosphamide
patients experienced a more
significant dose difference compared
with taller patients. All doses were
calculated according to the ASBMT
recommendations in Table 2.
A normal BMI is defined as a value
between 18.5 and 24.9. 65% of HSCT
patients had a BMI >25 (overweight),
and 26% of HSCT patients had a BMI
>30 (obese). Greater variations in
calculated IBW were seen in women,
which correlates with previous
research suggesting that Devine
underestimates IBW in this cohort
(Shah 2006). The dose of busulfan,
carmustine, and cyclophosphamide
calculated using our novel IBW
calculator was still less than the dose
actually received by the patient, since
we do not routinely apply the ASBMT
guidelines in our institution.
There is a 12% increase in IBW
calculated using our new formula,
compared to the established Devine
formula, and significant changes to
calculated doses for busulfan,
carmustine, and cyclophosphamide.
Further research is required to validate
this method of IBW determination.
References
1.Bubalo, J. Conditioning Chemotherapy Dose Adjustment in Obese Patients: A Review and
Position Statement by the American Society for Blood And Bone Marrow Transplantation
Practice Guidelines Committee, January 2014
2.Devine BJ. Gentamicin therapy. Drug Intell Clin Pharm. 1974;8:650–655.
3.Shah B., Sucher K., Hollenbeck C.B. Comparison of Ideal Body Weight Equations and Pub-
lished Height-Weight Tables with Body Mass Index Tables for Healthy Adults in the Unit-
ed States . Nutrition in Clinical Practice, 2006, 21 (3) , pp. 312-319.
Introduction Method
Key Findings
Discussion
Conclusion
Graph 1: % Difference between IBWD and IBWBMI by Height
Graph 2: % Dose Increase when using IBWBMI over IBWD
Table 1: IBW Formulas Examined
IBWD
Men: 50 kg + 2.3 kg/ each inch over 5 feet
Women: 45.5 + 2.3 kg/ each inch over 5 feet
IBWBMI 24.9 × (Height in meters)2
= IBWBMI
Table 2: ASBMT Dosing Recommendations (Bubalo 2014)
Busulfan
Weight-based (mg/kg) using ABW25
for all patients above their IBW
Carmustine
For patients >120% IBW, utilise BSA
with ABW25 to calculate BSA
Cyclophosphamide Use IBW for all adult patients
Adjusted Body Weight: ABW25= IBW × 0.25(TBW–IBW)
BSA (Body Surface Area), TBW (Total Body Weight)