IGF-I and IGF Binding Protein-3 Levels during Initial GH Dosage Step-Up Are Indicators of GH Sensitivity in GH-Deficient Children and Short Children Born Small for Gestational Age

Effective growth hormone replacement with once-weekly somapacitan in Japanese children with growth hormone deficiency: Results from REAL4, a phase 3 clinical trial

OBJECTIVE

Somapacitan is a long-acting growth hormone (GH) derivative developed for the treatment of GH deficiency (GHD). This study evaluates the efficacy and tolerability of somapacitan in Japanese children with GHD after 104 weeks of treatment and after switch from daily GH.

DESIGN

Subanalysis on Japanese patients from a randomised, open-labelled, controlled parallel-group phase 3 trial (REAL4, NCT03811535).

PATIENTS AND MEASUREMENTS

Thirty treatment-naïve patients were randomised 2:1 to somapacitan (0.16 mg/kg/week) or daily GH (0.034 mg/kg/day) up to Week 52, after which all patients received somapacitan. Height velocity (HV; cm/year) at Weeks 52 and 104 were the primary measurements. Additional assessments included HV SD score (SDS), height SDS, bone age, insulin-like growth factor-I (IGF-I) SDS, and observer-reported outcomes.

RESULTS

At Week 52, observed mean HV was similar between treatment groups (10.3 vs. 9.8 cm/year for somapacitan and daily GH, respectively). Similar HVs between groups were also observed at Week 104: 7.4 cm/year after continuous somapacitan treatment (soma/soma) and 7.9 cm/year after 1-year somapacitan treatment following switch from daily GH (switch). Other height-related endpoints supported continuous growth. IGF-I SDS increased in both groups with mean IGF-I SDS within -2 and +2 during the study. Somapacitan was well tolerated, one mild injection site reaction was reported, with no reports of injection site pain. Patient preference questionnaires showed that most patients and their caregivers (90.9%) who switched treatment at Week 52 preferred once-weekly somapacitan over daily GH treatment.

CONCLUSIONS

Somapacitan showed sustained efficacy in Japanese children with GHD over 104 weeks and for 52 weeks after switching from daily GH. Somapacitan was well tolerated and preferred over daily GH.

Growth hormone treatment for extremely low birthweight children born small for gestational age

BACKGROUND

The effectiveness of growth hormone (GH) treatment for height gain in short-stature children born small for gestational age (SGA) with extremely low birthweight (ELBW; birthweight <1,000 g) remains largely unknown.

METHODS

In study 1, 35 prepubertal Japanese children born SGA with ELBW were categorized into three groups based on the presence or absence of catch-up growth by age 3 (CU(+) and CU(-), respectively) and GH treatment (GH(+) and GH(-), respectively). Height standard deviation (SD) scores (HT-SDS) in the CU-/GH+ group (n = 19) were compared with those in the age-matched CU+/GH- (n = 9) and CU-/GH- groups (n = 7). In study 2, 66 prepubertal Japanese SGA children treated with GH were divided into three groups by birthweight: <1,000 g (n = 19), 1,000-2,000 g (n = 20), and >2,000 g (n = 27). Changes in HT-SDS during the initial 3 years of GH treatment were compared among the three groups.

RESULTS

In study 1, the mean HT-SDS in the CU-/GH+ group (-1.15 SD) was similar to that in the CU+/GH- group (-1.39 SD) but higher than that in the CU-/GH- group (-2.24 SD). In study 2, GH achieved a height gain of +1.62 SD in the ELBW group, which was similar to that in the other groups (1,000-2,000 g: +1.46 SD, >2,000 g: +1.53 SD).

CONCLUSIONS

Growth hormone treatment in short-stature children born SGA with ELBW increased HT-SDS, which was similar to that in SGA children born with a birthweight ≥1,000 g. These results indicate that GH treatment may be an effective approach to promote adequate growth recovery for short-stature children born SGA with ELBW.

What is the evidence for beneficial effects of growth hormone treatment beyond height in short children born small for gestational age? A review of published literature

Background An increasing body of evidence supports the view that both an adverse intrauterine milieu and rapid postnatal weight gain in children born small for gestational age (SGA) contribute towards the risk for the development of chronic diseases in adult life. Content The aim of this review was to identify and summarize the published evidence on metabolic and cardiovascular risk, as well as risk of impaired cardiac function, intellectual capacity, quality of life, pubertal development and bone strength among children born SGA. The review will then address whether growth hormone (GH) therapy, commonly prescribed to reduce the height deficit in children born SGA who do not catch up in height, increases or decreases these risks over time. Summary Overall, there are limited data in support of a modest beneficial effect of GH therapy on the adverse metabolic and cardiovascular risk observed in short children born SGA. Evidence to support a positive effect of GH on bone strength and psychosocial outcomes is less convincing. Outlook Further evaluation into the clinical relevance of any potential long-term benefits of GH therapy on metabolic and cardiovascular endpoints is warranted.

Evaluation of IGF1/IGFBP3 Molar Ratio as an Effective Tool for Assessing the Safety of Growth Hormone Therapy in Small-for-gestational-age, Growth Hormone-Deficient and Prader-Willi Children

OBJECTIVE

IGF1 concentration is the most widely used parameter for the monitoring and therapeutic adaptation of recombinant human growth hormone (rGH) treatment. However, more than half the variation of the therapeutic response is accounted for by variability in the serum concentrations of IGF1 and IGFBP3. We therefore compared the use of IGF1/IGFBP3 molar ratio with that of IGF1 concentration alone.

METHODS

We selected 92 children on rGH for this study and assigned them to three groups on the basis of growth deficiency etiology: small for gestational age (SGA), GH deficiency (GHD) and Prader-Willi syndrome (PWS). Plasma IGF1 and IGFBP3 concentrations and their molar ratio were determined.

RESULTS

Before rGH treatment, mean IGF1/IGFBP3 molar ratio in the SGA, GHD and PWS groups was 0.14±0.04, 0.07±0.01 and 0.12±0.02, respectively. After the initiation of rGH treatment, these averages were 0.19±0.07, 0.20±0.08 and 0.19±0.09, within the normal range for most children, even at puberty and despite some significant increases in serum IGF1 levels.

CONCLUSION

We consider IGF1/IGFBP3 molar ratio to be a useful additional parameter for assessing therapeutic safety in patients on rGH, and for maintaning the values within the normal range for age and pubertal stage.

Idiopathic short stature and growth hormone sensitivity in prepubertal children

OBJECTIVE

We compared growth hormone sensitivity to an insulin-like growth factor I (IGF-I) generation test in children with idiopathic short stature (ISS) and of normal stature (NS) across the birthweight range.

METHODS

Forty-six prepubertal children (~7.1 years) born at term were studied: ISS (n = 23; 74% boys) and NS (n = 23; 57% boys). Children underwent a modified IGF-I generation test with recombinant human growth hormone (rhGH; 0.05 mg/kg/d) over four consecutive days. Hormonal concentrations were measured at baseline and day 5.

RESULTS

Children with idiopathic short stature were 1.90 SDS lighter (P < 0.0001) but had 4.5% more body fat (P = 0.0007) than NS children. Overall, decreasing birthweight SDS across the normal range (-1.9 to +1.5 SDS) was associated with lower percentage IGF-I response to rhGH stimulation in univariable (r = 0.45; P = 0.002) and multivariable models (β = 24.6; P = 0.006). Plasma IGF-I concentrations rose in both groups with rhGH stimulation (P < 0.0001). GHBP levels (P = 0.002) were suppressed in ISS children (-19%; P = 0.029) but increased among NS children (+18%; P = 0.028), with contrasting responses also observed for leptin and IGFBP-1. Further, the increase in insulin concentrations in response to rhGH stimulation was ~3-fold greater in NS children (142% vs 50%; P = 0.006).

CONCLUSIONS

A progressive decrease in birthweight SDS was associated with a reduction in GH sensitivity in both NS and ISS children. Thus, the lower IGF-I response to rhGH stimulation in association with decreasing birthweight indicates that the ISS children at the lower end of the birthweight spectrum may have partial GH resistance, which may contribute to their poorer growth.

Poor growth response during the first year of growth hormone treatment in short prepubertal children with growth hormone deficiency and born small for gestational age: a comparison of different criteria

Background

There is no consensus on the definition of poor growth response after the first year of growth hormone (GH) treatment. We determined the proportion of poor responders identified by different criteria in children with GH deficiency (GHD) and born small for gestational age (SGA). The second aim was to analyze the IGF-1 response in poor growth responders.

Methods

First-year height data of 171 SGA and 122 GHD children who remained prepubertal during the first GH treatment year were retrieved from the BESPEED database and analyzed. Criteria for poor first-year response/responsiveness were: change in height (∆Ht) SDS<0.3 or<0.5, height velocity (HV) SDS<0.5 or <1 based on the population reference, HV SDS<- 1 based on the KIGS expected HV curve (HV Ranke SDS), studentized residual (SR) <- 1 in the KIGS first-year prediction model.

Results

∆Ht SDS<0.5 gave the highest percentage poor responders (37% SGA, 26% GHD). Although % poor responders were comparable for ∆Ht SDS<0.3, HV SDS<+ 0.5, HV SDS<+ 1, SR<- 1, and HV Ranke SDS<- 1, these criteria did not always identify the same patients as poor responders. Among the poor growth responders 24% SGA and 14% GHD patients had an IGF-1 increase < 40%.

Conclusions

The different response criteria yield high but comparable percentages poor responders, but identify different patients. This study does not provide evidence that one criterion is better than another. A limited IGF-1 generation is not the major reason for a poor growth response in the first year of GH treatment in SGA and GHD children.

Trial registration

Retrospectively registered.

Growth Hormone Treatment in Children Born Small for Gestational Age (SGA)

Introduction: Growth failure is a common consequence in small for gestational age (SGA) children.

Patients and Methods: The growth patterns and serum insulin like growth factor 1 (IGF1) concentrations before and after the 1st year under growth hormone treatment of 32 short stature SGA born children have been evaluated. In addition, we investigated the insulin like growth factor 1 receptor (IGF1R) exon 2 as a hotspot for IGF1R genetic alterations. It is of note that no dysmorphic features were observed in this group of children.

Results: The tests for pituitary reserve were within normal ranges for all 32 patients. Growth hormone (GH) treatment (0.037 mg/kg/day) was initiated at the mean age of 9.32±3.19 years. Growth velocity increased yearly from −1.80 SDS after the first year to −0.03 SDS in the sixth year of treatment. Their IGF1 serum concentrations before treatment were age and sex appropriate, while during treatment a significant increase was observed fitting in the upper third of the normal range: before the treatment IGF1 SDS was 0.84±1.78 after 1st year the concentrations increased to IGF1 SDS 0.94±2.23. No genetic alterations were found in the IGF1R exon 2 by PCR analysis.

Conclusions: Herein we present 32 short stature SGA children with no dysmorphic features treated with GH. They all had increased growth velocity and entered the normal growth range on their growth charts. No side-effects were observed. GH treatment in children with no genetic alterations on the IGF1R exon 2 is safe and efficient in treating SGA children with short stature.

Impact of the underlying etiology of growth hormone deficiency on serum IGF-I SDS levels during GH treatment in children

CONTEXT

Regular monitoring of serum IGF-I levels during growth hormone (GH) therapy has been recommended, for assessing treatment compliance and safety.

OBJECTIVE

To investigate serum IGF-I SDS levels during GH treatment in children with GH deficiency, and to identify potential determinants of these levels.

DESIGN, PATIENTS AND METHODS

This observational cohort study included all patients (n = 308) with childhood-onset non-acquired or acquired GH deficiency (GHD) included in the database of a single academic pediatric care center over a period of 10 years for whom at least one serum IGF-I SDS determination during GH treatment was available. These determinations had to have been carried out centrally, with the same immunoradiometric assay. Serum IGF-I SDS levels were determined as a function of sex, age and pubertal stage, according to our published normative data.

RESULTS

Over a median of 4.0 (2-5.8) years of GH treatment per patient, 995 serum IGF-I SDS determinations were recorded. In addition to BMI SDS, height SDS and GH dose (P < 0.01), etiological group (P < 0.01) had a significant effect on serum IGF-I SDS levels, with patients suffering from acquired GHD having higher serum IGF-I SDS levels than those with non-acquired GHD, whereas sex, age, pubertal stage, treatment duration, hormonal status (isolated GHD (IGHD) vs multiple pituitary hormone deficiency (MPHD)) and initial severity of GHD, had no effect.

CONCLUSIONS

These original findings have important clinical implications for long-term management and highlight the need for careful and appropriate monitoring of serum IGF-I SDS and GH dose, particularly in patients with acquired GHD, to prevent the unnecessary impact of potential comorbid conditions.

Insulin-like growth factor binding-protein-3 (IGFBP-3)

The IGF system comprises two IGFs (IGF-1, IGF-2), two IGF-receptors (IGF-R1, IGF-R2), and six IGF binding proteins (IGFBPs) with a high affinity for IGFs. The IGFBPs, of which IGFBP-3 is the most abundant in postnatal blood, link with IGFs and prevent them from being degraded; they also facilitate IGF transport through body compartments. The interaction between IGFs and their specific receptors is partly regulated by structural modifications inherent to the IGFBPs. IGFBPs also have IGF-independent biological effects. Since serum IGFBP-3 is GH-dependent and correlates quantitatively with GH secretion, its measurement is useful in tests of abnormal GH secretion. Particularly during childhood, IGFBP-3 values play an important role in ascertaining alterations in GH secretion and action (i.e., primary IGF deficiency states). A new role for IGFBP-3 and other IGFBPs with natural or altered structures is likely to be established through current studies investigating their application in promoting apoptotic processes in malignancies.

Comparison of weight- vs body surface area-based growth hormone dosing for children: implications for response

OBJECTIVE

To compare weight (per kg)- vs body surface area (BSA, per m(2) )-based growth hormone (GH) dosing formats in children and to derive a useful conversion formula between the two formats.

PATIENTS AND DESIGN

Growth hormone doses (>33,000) from 1874 children were obtained from the national Australian database (OZGROW) and used to derive conversion formulae and to confirm the accuracy of a conversion formula based on a weight-only BSA estimate. A further 27,000 doses were used to test the accuracy of all formulae. The best conversion formula was used to compare weight- and surface area-based GH dosing, which included an analysis of first year response (∆SDS height or growth velocity, GV).

MEASUREMENTS

Growth hormone doses in mg/m(2) /wk and mg/kg/wk, dose estimates, residuals, first year ∆SDS, first year GV.

RESULTS

The formula, [Formula: see text] based on a weight-only BSA estimate, provides accurate dose conversion (mean residual, 0·005 mg/kg/week). A constant mg/m(2) /week dose expressed in terms of mg/kg/week declines quickly with increasing body weight to approximately 15 kg after which the decline continues although less dramatically. For Australian patients, despite an increase in mean per m(2) dose with increased starting weight/age, the per kg dose decreased. This was associated with a greater decline in first year GV than estimated if a per kg dose had been maintained.

CONCLUSIONS

Growth hormone doses can be accurately converted between formats. Surface area-based GH dosing is likely to result in a reduced height response as children become heavier when compared with weight-based GH dosing.

Personalized approach to growth hormone treatment: clinical use of growth prediction models

The goal of growth hormone (GH) treatment in a short child is to attain a fast catch-up growth toward the target height (TH) standard deviation score (SDS), followed by a maintenance phase, a proper pubertal height gain, and an adult height close to TH. The short-term response variable of GH treatment, first-year height velocity (HV) (cm/year or change in height SDS), can either be compared with GH response charts for diagnosis, age and gender, or with predicted HV based on prediction models. Three types of prediction models have been described: the Kabi International Growth Hormone Study models, the Gothenburg models and the Cologne model. With these models, 50-80% of the variance could be explained. When used prospectively, individualized dosing reduces the variation in growth response in comparison with a fixed dose per body weight. Insulin-like growth factor-I-based dose titration also led to a decrease in the variation. It is uncertain whether adding biochemical, genetic or proteomic markers may improve the accuracy of the prediction. Prediction models may lead to a more evidence-based approach to determine the GH dose regimen and may reduce the drug costs for GH treatment. There is a need for user-friendly software programs to make prediction models easily available in the clinic.

Final height and insulin-like growth factor-1 in children with medulloblastoma treated with growth hormone

PURPOSE

Medulloblastoma is a highly malignant childhood brain tumor. Survival from medulloblastoma is increasing. This study was performed to examine growth outcomes, insulin-like growth factor-1(IGF-1), and response to growth hormone (GH) treatment in children with medulloblastoma.

METHODS

Retrospective analysis of 34 children treated with GH for medulloblastoma was performed. We evaluated serum IGF-1 and insulin-like growth factor binding protein-3 concentrations. Further, we examined growth status and changes with GH treatment according to treatment modality.

RESULTS

GH deficiency was observed in 28 patients (82 %). The initial height at the start of GH treatment was -2.35 ± -1.53 standard deviation score (SDS) and increased to -1.85 ± -1.28 SDS by 1 year, -1.64 ± -1.46 SDS by 2 years, and -1.42 ± -1.49 SDS by 3 years after GH treatment. The final height was -1.54 ± -1.06 SDS. Gender, surgical method, tumor location, tumor size, and type of radiation did not correlate with height gain. A younger age at the initiation of GH treatment correlated with height gain. The initial serum IGF-1 concentration was -1.73 ± -0.42 and increased significantly to -0.74 ± -0.21 SDS by 1 year after GH treatment. The serum IGF-1 SDS increment correlated significantly with height gain.

CONCLUSIONS

Beginning GH treatment at a younger age was an important prognostic factor for growth outcome. Serum IGF-1 increment correlated with height gain during GH treatment. Thus, early GH treatment and analysis of serum IGF-1 might be helpful for improving final height or growth outcome.

Towards optimal treatment with growth hormone in short children and adolescents: evidence and theses

Treatment with growth hormone (GH) has become standard practice for replacement in GH-deficient children or pharmacotherapy in a variety of disorders with short stature. However, even today, the reported adult heights achieved often remain below the normal range. In addition, the treatment is expensive and may be associated with long-term risks. Thus, a discussion of the factors relevant for achieving an optimal individual outcome in terms of growth, costs, and risks is required. In the present review, the heterogenous approaches of treatment with GH are discussed, considering the parameters available for an evaluation of the short- and long-term outcomes at different stages of treatment. This discourse introduces the potential of the newly emerging prediction algorithms in comparison to other more conventional approaches for the planning and evaluation of the response to GH. In rare disorders such as those with short stature, treatment decisions cannot easily be deduced from personal experience. An interactive approach utilizing the derived experience from large cohorts for the evaluation of the individual patient and the required decision-making may facilitate the use of GH. Such an approach should also lead to avoiding unnecessary long-term treatment in unresponsive individuals.

Comparative evaluation of short-term biomarker response to treatment for growth hormone deficiency in Chinese children with growth hormone deficiency born small for or appropriate for gestational age: a randomized phase IV open-label study

OBJECTIVES

To compare the response between Chinese children with growth hormone deficiency (GHD) born either small for gestational age (SGA) or appropriate for gestational age (AGA) after 4 weeks of recombinant human growth hormone (r-hGH) therapy.

METHODS

This was a phase IV, open-label, multicenter, interventional study (NCT01187550). Prepubertal children with GHD received open-label treatment with daily r-hGH (0.033 mg/kg) for 4 weeks. Serum levels of insulin-like growth factor I (IGF-I) and insulin-like growth factor-binding protein 3 (IGFBP3), and metabolic markers (including fasting glucose, insulin, total cholesterol, and homeostasis model assessment of insulin resistance) were assessed at baseline and after 4 weeks of treatment, and were analyzed according to patient subgroup (SGA or AGA).

RESULTS

A total of 205 children with GHD (mean age 10.4 years; 175 AGA, 30 SGA) were included in the analysis. Mean baseline serum IGF-I and IGFBP3 standard deviation scores (SDS) across the whole patient population were lower than the population norms (mean values: -2.1 SDS for IGF-I and -1.2 SDS for IGFBP3), with no significant differences between the two patient subgroups. After 4 weeks, IGF-I and IGFBP3 levels increased by 1.0 SDS (p < 0.001) and 0.34 SDS (p < 0.001), respectively, but no significant differences were found between the two patient subgroups for growth-related or metabolic markers.

CONCLUSIONS

For children with GHD born SGA, IGF-I and IGFBP3 are short-term biomarkers of responsiveness to treatment with growth hormone, as for children with GHD born AGA.

Long-term safety and efficacy of the recombinant human growth hormone Omnitrope® in the treatment of Spanish growth hormone deficient children: results of a phase III study

INTRODUCTION

This phase III study in growth hormone (GH) deficient (GHD) children with growth retardation was designed to demonstrate the safety and efficacy of longterm treatment with the recombinant human GH Omnitrope® (Sandoz BioPharmaceuticals, Holzkirchen, Germany).

METHODS

Treatment-naïve, prepubertal Spanish children (n=70) with isolated GHD were treated with Omnitrope 0.03 mg/kg/day subcutaneously. Changes in height, height standard deviation score (HSDS), height velocity (HV), HV standard deviation score (HVSDS), serum insulin-like growth factor (IGF)-1, and insulin-like growth factor binding protein (IGFBP)-3 levels were recorded.

RESULTS

Omnitrope treatment provided a good growth response after 4 years, shown by a significant increase in mean body height (31.1 cm [95% CI: 29.6-32.6]), HSDS (Tanner) (1.42 [1.13-1.70]), HV (2.4 cm [1.7-3.1]), and HVSDS values (3.5 [2.7-4.3]). Mean IGF-1 and IGFBP-3 serum levels also increased significantly.

CONCLUSION

At a dose of 0.03 mg/kg/day, Omnitrope was safe, effective, and well tolerated during long-term treatment of children with GHD.

Systematic review of the clinical effectiveness of Genotropin (somatropin) in children with short stature

Genotropin (somatropin) is licensed for the treatment of children with growth hormone deficiency, Prader-Willi syndrome, Turner syndrome, chronic renal insufficiency and in children born small for gestational age. This systematic review (SR) evaluated the clinical efficacy and effectiveness of Genotropin in these conditions to inform a NICE Technology Appraisal of growth hormone for the treatment of growth failure in children. Search terms were used to search seven databases, including Medline and Embase, for English language studies. Randomised controlled trials (RCTs) or observational studies investigating Genotropin in children were included. Out of 30 RCTs identified, one reported final height data. Eleven observational studies reported final height and seven were based on the Pfizer International Growth Survey (KIGS). This SR highlights the lack of long-term RCTs reporting final height data and other important qualitative outcomes, such as quality of life. Observational data, such as those from KIGS, remain vital for informing therapy.

Pharmacokinetic and pharmacodynamic profile of a new sustained-release GH formulation, LB03002, in children with GH deficiency

OBJECTIVE

LB03002 is a novel, sustained-release recombinant human GH, developed for once-a-week s.c. injection. To evaluate the suitability for long-term GH replacement therapy in children with GH deficiency (GHD), the present study assessed the pharmacokinetic (PK) and pharmacodynamic (PD) profiles of LB03002 at three doses.

STUDY DESIGN AND PATIENTS

The randomised, comparator-controlled, assessor-blinded, phase II study assessed 37 (24 boys, 13 girls) pre-pubertal, GH-naïve children with GHD, in 11 European centres, for PK and PD analyses. GH, IGF1 and IGFBP3 concentrations were measured following the last daily GH dose and the first and 13th once-a-week administration of LB03002 at doses of 0.2, 0.5 or 0.7 mg/kg.

RESULTS

GH C(max) values after the three doses of LB03002 were increased up to fourfold, with a clear dose proportionality. For each LB03002 dose, GH area under the concentration versus time curve did not increase from the first to 13th (month 3) administration, indicating no accumulation of circulating GH. IGF1 C(max) showed a progressive increase during LB03002 administration. Conversely, IGFBP3 showed a rapid increase in C(max). IGF1 SDS were fully normalised after 3 months of treatment, whereas IGFBP3 SDS were already in the normal range for all the three LB03002 dosages after 1 week.

CONCLUSIONS

At the doses used, LB03002 has a suitable profile for long-term treatment to promote growth in children with GHD. The quantitative changes in IGF1 and IGFBP3 indicate adequate stimulation of the IGF system by LB03002 and the pattern of increase is comparable with that seen in GHD children in a standard IGF1 generation test using daily GH.

Recombinant human growth hormone for children born small for gestational age: meta-analysis confirms the consistent dose-effect relationship on catch-up growth

BACKGROUND

The optimal treatment regimen of recombinant human GH (r-hGH) for short children born small for gestational age (SGA) is still under discussion.

METHODS

A meta-analysis was performed of existing clinical trials that investigated the treatment of r-hGH in short children diagnosed SGA or with intrauterine growth retardation to determine the relationship between the daily r-hGH dose (placebo/no treatment; 0.033 mg/kg/day; 0.067 mg/kg/day) and the effect on growth [change in height-SD score (SDS) for chronological age]. A mathematical model describing the dose-response relationship was produced, and growth response (gain in height-SDS) to 2 yr of r-hGH 0.033 mg/kg/day [somatropin (rDNA origin) for injection; Serono] was estimated and compared with the response to other r-hGH formulations.

RESULTS

The relationship between r-hGH dose and 2-yr growth response was described by an equation. The equation yielded a mean difference in height- SDS gain of 0.48 (0.35) between r-hGH 0.033 and 0.067 mg/kg/day in favor of the higher dose. The height-SDS gain after 2 yr of Serono r-hGH formulation, 0.033 mg/kg/day was estimated as 1.2. Comparison of this estimate to the growth response to 2-yr treatment at 0.033 mg/kg/day of other r-hGH formulations (mean difference in height-SDS 0.05, lower limit of the 95% confidence interval=-0.15) confirmed that growth response to Serono r-hGH formulation 0.033 mg/kg/day is an inferred response estimated to be within the range of observed responses to a (non-Serono formulation) r-hGH dose of 0.033 mg/kg/day.

CONCLUSION

There is a clear dose-response relationship for r-hGH in the treatment of short children born SGA and the analysis confirmed that treatment with Serono r-hGH formulation 0.033 mg/kg/day should provide a meaningful therapeutic response.