Growth Hormone Dosing Estimations Based on Body Weight Versus Body Surface Area.

INTRODUCTION: Body weight (BW) and body surface area (BSA)-based dosing regimens have been recommended for recombinant human growth hormone (rhGH) replacement, with the assumption that they are equally efficacious. We wanted to determine if higher or lower treatment may result from either of the two regimens based on the initial prescribed doses and the growth responses of the patients throughout the first year of therapy.

METHODS: The retrospective study included 60 children from two different centers, aged 1-18 years, with the diagnosis of idiopathic isolated growth hormone deficiency(IGHD). BW-based dosing in mcg/kg/day, which is routinely employed in our clinical practice, was converted to BSA in mg/m2 /day to determine the equivalent amounts of the given rhGH. Those with a BSA-to-BW ratio of more than 1 were allocated to the "relatively higher-dosed group", while the remaining patients were assigned to the "relatively lower-dosed" group. Patients with a height gain greater than 0.5 standard deviation (SD) score at the end of one year were classified as the height at goal (HAG), whereas those with a height gain of less than 0.5 SD score were assigned as the height not at goal (NHAG).

RESULTS: The study included 60 patients (18 girls, 42 boys) with IGHD. Thirty-six (60%) patients had HAG after one year of treatment. The ratio of dosing based on BSA to BW was negatively correlated both with the ages and BMI levels of the patients, leveling off at the age of 11.7 at a BMI of 18.3 kg/m2 . The relative dose estimations (relatively higher-, lower-dosed groups) differed significantly between the patients with HAG and NHAG (p= 0.006). If dosing had been based on BSA rather than BW, the majority of patients with HAG (61%) would have been dosed relatively higher, whereas those with NHAG (75%) would have been dosed relatively lower.

CONCLUSION: We have evaluated BSA and BW-based strategies among a homogenous cohort of patients with IGHD. GH doses based on BSA compared to BW-based dosing may result in the administration of higher doses to children younger than 11.7 years of age with BMI levels less than 18.3 kg/m2 and lower doses to children older than 11.7 years of age with BMI levels more than 18.3 kg/m2 . Dosing based on BW rather than BSA may be preferable in children younger than 12 years old who are not obese.