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)