Pharmacotherapeutic group: Pituitary and hypothalamic hormones and analogues, somatropin and somatropin agonists, ATC code: H01AC07.
Mechanism of action
Somapacitan is a long-acting recombinant human growth hormone derivative. It consists of 191 amino acids similar to endogenous human growth hormone, with a single substitution in the amino acid backbone (L101C) to which an albumin binding moiety has been attached. The albumin binding moiety (side-chain) consists of a fatty acid moiety and a hydrophilic spacer attached to position 101 of the protein.
The mechanism of action of somapacitan is either directly via the GH-receptor and/or indirectly via IGF-I produced in tissues throughout the body, but predominantly by the liver.
When growth hormone deficiency is treated with somapacitan a normalisation of body composition (i.e., decreased body fat mass, increased lean body mass) and of metabolic action is achieved.
Somapacitan stimulates skeletal growth in paediatric patients with GHD as a result of effects on the growth plates (epiphyses) of bones, see section 5.3.
Pharmacodynamic effects
IGF-I
IGF-I is a generally accepted biomarker for efficacy in GHD.
A dose-dependent IGF-I response is induced following somapacitan administration.
A steady state pattern in IGF-I responses is reached after 1-2 weekly doses.
The IGF-I levels fluctuate during the week. The IGF-I response is maximal after 2 to 4 days. Compared with daily GH treatment, the IGF-I profile of somapacitan differs, see Figure 1.
In paediatric GHD patients somapacitan produces a dose linear IGF-I response, with a change of 0.02 mg/kg on average resulting in a change in IGF-I standard deviation score (SDS) of 0.32.

Figure 1: Model-derived IGF-I profiles during steady state of somapacitan and somatropin (based on data from adult GHD)
Clinical efficacy and safety
Paediatric GHD
REAL 4 (phase 3)
The efficacy and safety of once weekly somapacitan was evaluated in a 52 weeks randomised, multi-center, open-label, active-controlled, parallel-group phase 3 trial (REAL 4) in 200 treatment-naïve, paediatric patients with GHD. Patients were randomised to 0.16 mg/kg/week once weekly somapacitan (N=132) or 0.034 mg/kg/day once daily somatropin (N=68).
At baseline, the 200 patients had a mean age of 6.4 years (range: 2.5 to 11 years). 74.5% of the patients were male.
The annualised height velocity at week 52 was similar for somapacitan and somatropin (Table 4).
Table 4: Growth results at week 52 in paediatric patients with GHD
| | Once-weekly somapacitan (N=132) | Once-daily somatropin (N=68) | Estimate of treatment difference (95% CI) (somapacitan minus somatropin) |
| Annualised height velocity (cm/year) | 11.2 | 11.7 | -0.5 [-1.1; 0.2] |
In accordance with this, changes at week 52 compared to baseline with respect to the height SDS and IGF-I SDS were also similar for somapacitan and somatropin (Table 5).
Table 5: Height SDS and IGF-I SDS in paediatric patients with GHD – 52 weeks treatment
| | Once-weekly somapacitan (N=132) | Once-daily somatropin (N=68) | Estimate of treatment difference (95% CI) (somapacitan minus somatropin) |
| Height SDS, baselinea | -2.99 | -3.47 | |
| Height SDS, change from baseline | 1.25 | 1.30 | -0.05 [-0.18; 0.08] |
| IGF-I SDS, baselinea | -2.03 | -2.33 | |
| IGF-I SDS, week 52a | 0.28 | 0.10 | |
| IGF-I SDS level change from baseline | 2.36 | 2.33 | 0.03 [-0.30; 0.36] |
a Observed mean
The vast majority of paediatric patients (96.9%) in the trial achieved an average IGF-I SDS level within normal range (-2 to +2) after 52 weeks of treatment with once weekly somapacitan (Table 6). A low number of patients had average IGF-I SDS above +2 (2.3%) and no patients had average IGF-I SDS above +3.
Table 6: Average IGF-I SDS values after 52 weeks of treatment of paediatric patients with GHD with once weekly somapacitan
| IGF-I SDS category | Week 52 average (N=132) |
| <-2 | 0.8% |
| -2 to 0 | 21.2% |
| 0 to +2 | 75.8% |
| +2 to +3 | 2.3% |
| >+3 | 0 |
REAL 3 (phase 2)
A total of 59 GH treatment-naïve GH-deficient paediatric patients completed a 26-week main period and a 26-week extension in a 4-arm parallel group trial with once weekly somapacitan at dose levels of 0.04, 0.08 and 0.16 mg/kg/week and active control arm of 0.034 mg/kg/day daily somatropin. The patients continued in a 104-week open-label safety extension parallel arms with somapacitan 0.16 mg/kg/week and daily somatropin 0.034 mg/kg/day. All patients were afterwards transferred to once weekly somapacitan 0.16 mg/kg/week in a 208-week long-term safety extension.
Treatment with once weekly somapacitan led to continuous treatment benefits up to at least week 208. Height SDS was -1.06 (change from baseline: 2.85) in 38 patients.
Height outcome obtained at week 208 in patients switching from 0.034 mg/kg/day daily somatropin to 0.16 mg/kg/week once weekly somapacitan at week 156 indicated that treatment benefits with daily GH treatment are maintained after switching to once weekly somapacitan.
Mean IGF-I SDS remained within the normal range for all groups.
Adult GHD
In a 34-week placebo-controlled (double-blind) and active-controlled (open) trial, 301 treatment-naïve adult patients with GHD were randomised (2:1:2) and 300 were exposed to once-weekly somapacitan or to placebo or to daily somatropin for a 34-week treatment period (main phase of the trial). The patient population had a mean age of 45.1 years (range 23-77 years; 41 patients were 65 years or above), 51.7% were females, and 69.7% had adult onset GHD.
A total of 272 adult GHD patients who completed the 34-week main phase continued in a 53-week open-label extension period. Subjects on placebo were switched to somapacitan and patients on somatropin were re-randomised (1:1) to either somapacitan or somatropin.
Observed clinical effects for the main endpoints in the main treatment phase (Table 7) and extension treatment phase (Table 8) are presented below.
Table 7: Results at 34 weeks
| Change from baseline at 34 weeksa | somapacitan | somatropin | placebo | Difference somapacitan -placebo [95% CI] p-value | Difference somapacitan- somatropin [95% CI] |
| Number of subjects (N) | 120 | 119 | 61 | | |
| Truncal fat % (Primary endpoint) | -1.06 | -2.23 | 0.47 | -1.53 [-2.68; -0.38] 0.0090b | 1.17 [0.23; 2.11] |
| Visceral adipose tissue (cm2) | -10 | -9 | 3 | -14 [-21; -7] | -1 [-7; 4] |
| Appendicular skeletal muscle mass (g) | 558 | 462 | -121 | 679 [340; 1,019] | 96 [-182; 374] |
| Lean body mass (g) | 1,394 | 1,345 | 250 | 1144 [459; 1,829] | 49 [-513; 610] |
| IGF-I SDS level | 2.40 | 2.37 | -0.01 | 2.40 [2.09; 2.72] | 0.02 [-0.23; 0.28] |
Abbreviations: N = Number of subjects in full analysis set, CI = Confidence interval, DM=Diabetes mellitus. IGF-I SDS: Insulin-like growth factor-I standard deviation score.
a Body composition parameters are based on dual-energy X-ray absorptiometry (DXA) scanning.
b The primary analysis was a comparison of changes from baseline for somapacitan and placebo in truncal fat %. Changes in truncal fat % from baseline to the 34 week's measurements was analysed using an analysis of covariance model with treatment, GHD onset type, sex, region, DM and sex by region by DM interaction as factors and baseline as a covariate incorporating a multiple imputation technique where missing week 34 values were imputed based on data from the placebo group.
Post-hoc subgroup analysis of changes from baseline in truncal fat percentage (%) compared to placebo at week 34 showed an estimated treatment difference (somapacitan-placebo) of -2.49% [-4.19; -0.79] in men, -0.80% [-2.99; 1.39] in women not on oral oestrogen, -1.44% [-3.97; 1.09] in women on oral oestrogen.
Table 8: Results at 87 weeks
| Change from baseline at 87 weeksa | somapacitan/ somapacitan | somatropin/ somatropin | placebo/ somapacitan | somatropin/ somapacitan | Difference somapacitan/ somapacitan vs somatropin/somatropin [95% CI] |
| Number of subjects (N) | 114 | 52 | 54 | 51 | |
| Truncal fat % | -1.52 | -2.67 | -2.28 | -1.35 | 1.15 [-0.10; 2.40] |
| Visceral adipose tissue (cm2) | -6.64 | -6.85 | -10.21 | -8.77 | 0.22 [-10; 10] |
| Appendicular skeletal muscle mass (g) | 546.11 | 449.09 | 411.05 | 575.80 | 97.02 [-362; 556] |
| Lean body mass (g) | 1,739.05 | 1,305.73 | 1,660.56 | 1,707.82 | 433.32 [-404; 1271] |
a Body composition parameters are based on DXA scanning.
Observed and simulated IGF-I SDS levels in the clinical study
In the main phase of the clinical study IGF-I SDS values of 0 and above were overall achieved in 53% of somapacitan-treated adult GHD study patients after an 8-week dose titration period. This proportion was however lower in particular subgroups such as women on oral oestrogen (32%) and patients with childhood-onset (39%) (Table 9). Post-hoc simulation analyses indicated that the proportions of adult GHD patients achieving IGF-I SDS levels above 0 are expected to be higher in case somapacitan dose titration beyond 8 weeks would be allowed. In this simulation analysis, it was assumed that somapacitan dose titration was well-tolerated in all patients until the IGF-I SDS target range or a somapacitan dose of 8 mg per week would be achieved.
Table 9 Proportions of somapacitan-treated adult GHD patients with IGF-I SDS levels above 0
| Subgroups | Men | Women not on oral oestrogen | Women on oral oestrogen | Childhood-onset adult GHD | Adult-onset adult GHD | All |
| Observeda | 71% | 46% | 32% | 39% | 60% | 53% |
| Post-hoc simulations | 100% | 96% | 70% | 84% | 92% | 90% |
a The trial was designed to titrate towards a IGF-I SDS level above -0.5
Maintenance dose
Maintenance dose varies from person to person and between male and female patients. The average somapacitan maintenance dose observed in the phase 3 clinical trials was 2.4 mg/week.
Paediatric and adult GHD
Clinical safety
The safety profile of somapacitan was similar to the well-known safety profile of somatropin. No new safety issues were identified, see section 4.8.
Immunogenicity
Anti-drug antibodies (ADA) were uncommonly detected in paediatric patients (16/132). None of these antibodies were neutralising. No evidence of ADA impact on pharmacokinetics, efficacy or safety was observed. No anti-drug antibodies were detected in adult patients.
Paediatric population
The European Medicines Agency has waived the obligation to submit the results of studies with Sogroya in all subsets of the paediatric population in growth hormone deficiency (see section 4.2 for information on paediatric use).