Evenity (Romosozumab) in Children Under 12: What the Off-Label Evidence Actually Shows

Why Romosozumab Is Being Considered in Young Children at All

The adult approval rests on solid phase-3 data, but the drug's biology makes pediatric researchers pay close attention. Romosozumab blocks sclerostin, a glycoprotein encoded by the SOST gene that normally restrains bone formation. Children with loss-of-function mutations in SOST develop sclerosteosis, a condition marked by extremely dense bones. That natural experiment suggests sclerostin inhibition could be powerful in growing skeletons.

Pediatric fracture disorders, particularly osteogenesis imperfecta (OI), impose enormous morbidity. Bisphosphonates, mainly intravenous pamidronate and zoledronic acid, have been the standard of care for decades in children with OI. They reduce fracture rates but do not normalize bone quality or architecture. Romosozumab's anabolic mechanism, the ability to actually add new bone rather than only slow resorption, is therefore scientifically appealing for a disease driven by defective collagen matrix production.

The Sclerostin Biology in Growing Bone

Sclerostin expression varies across development. Studies in murine models show that Sost knockout mice have markedly increased cortical and trabecular bone mass, and this effect is evident from early post-natal life onward. A 2019 analysis published in Bone confirmed high SOST expression in pediatric osteocytes, suggesting the target is biologically present in young patients [1].

Wnt signaling, which romosozumab disinhibits by removing sclerostin's blocking action, is a master regulator of skeletal growth. The overlap between Wnt-driven longitudinal growth and romosozumab's proposed anabolic effect raises questions about whether the drug might influence growth plates, a concern absent in postmenopausal patients [2].

Why Bisphosphonates Alone Are Insufficient for Some Children

Intravenous zoledronic acid (0.05 mg/kg, given annually or biannually) reduces vertebral fracture incidence in children with OI by roughly 30 to 40% in cohort data, but the bones it preserves remain structurally abnormal. A 2021 systematic review in Osteoporosis International found that lumbar spine bone mineral density (BMD) Z-scores in children with moderate-to-severe OI rarely normalize on bisphosphonate therapy alone, with mean Z-scores persisting below negative 2.0 in many published series [3]. That residual deficit leaves a window for anabolic agents.

FDA Regulatory Status and What "Off-Label" Means Here

The FDA approved romosozumab in April 2019 under the brand name Evenity, with a label restricted to postmenopausal women at high fracture risk. The label carries a boxed warning about increased risk of myocardial infarction, stroke, and cardiovascular death relative to alendronate, data drawn from the ARCH trial (N=4,093) where the romosozumab arm showed 2.5% versus 1.9% major adverse cardiovascular events compared to alendronate at 33 months [4].

No pediatric studies were required under the Pediatric Research Equity Act (PREA) at the time of approval, partly because the approved indication does not exist in children. That exemption means the FDA has not reviewed any pediatric romosozumab data, and no formal pediatric labeling language exists [5].

Compassionate Use and Expanded Access

Physicians who want to use romosozumab off-label in a child under 12 have three realistic pathways. First, they may enroll the patient in a registered clinical trial. Second, they may apply for expanded access (single-patient IND) through the FDA, which requires a 15-day FDA review for non-emergency situations. Third, in some jurisdictions outside the United States, national ethics boards authorize compassionate use under local regulations.

The FDA's expanded access program for pediatric patients is described in 21 CFR Part 312, Subpart I. As of the 2023 update to PREA guidance, sponsors developing drugs for adult conditions that may affect children are encouraged, though not always compelled, to generate pediatric data [5].

Institutional Requirements

Any pediatric use outside a trial requires written informed consent from both parents or legal guardians, documentation of failed or inadequate standard therapy, endocrinology or metabolic bone disease specialist involvement, and in most institutions an Institutional Review Board (IRB) or ethics committee notification. These are not bureaucratic formalities. They protect both the child and the clinician.

Available Evidence: Case Reports, Case Series, and Early Trials

The evidence base for romosozumab in children under 12 is narrow. It consists almost entirely of case reports, small case series, and one or two early-phase investigational studies. No randomized controlled trial specifically targeting this age group has published results as of early 2025.

Osteogenesis Imperfecta Case Data

The most cited pediatric data come from case reports of children with severe OI (types III and IV) who received romosozumab after inadequate response to bisphosphonates. A 2022 case series published in JBMR Plus described four patients aged 4 to 11 years with OI types III or IV who received romosozumab 2.1 mg/kg (maximum 210 mg) monthly for 12 months. Lumbar spine BMD Z-scores improved by a mean of 1.3 standard deviations over the treatment year, and no fractures occurred during the treatment period [6]. The small sample and lack of a control group make this data hypothesis-generating, not practice-defining.

A separate German case report published in 2023 described an 8-year-old girl with OI type III who showed a 28% increase in lumbar spine areal BMD after 12 months of romosozumab, with maintenance of gains during a subsequent 12-month denosumab consolidation phase [7]. Post-treatment consolidation with an antiresorptive agent, either denosumab or a bisphosphonate, has been proposed to prevent the rapid bone loss that follows romosozumab discontinuation in adults.

Glucocorticoid-Induced Osteoporosis in Children

Children with inflammatory or autoimmune conditions requiring long-term glucocorticoids represent a second potential population. Glucocorticoids suppress Wnt signaling and increase sclerostin expression, creating a theoretical rationale for sclerostin inhibition in this setting [8]. No pediatric romosozumab data for glucocorticoid-induced osteoporosis in children under 12 has been published in peer-reviewed literature as of this writing, though ClinicalTrials.gov lists at least one observational protocol collecting this data prospectively.

Early Trial Activity

ClinicalTrials.gov identifier NCT04857983 is a phase-2 open-label study of romosozumab in children and adolescents with moderate-to-severe OI, with an age range starting at 5 years. The study uses a weight-based dosing schema (2.1 mg/kg monthly, capped at 210 mg) and includes DXA scanning, pQCT, and fracture recording as primary endpoints. Enrollment and early safety results from this study are expected to inform whether a randomized phase-3 trial is feasible [9].

The framework below summarizes how HealthRX's medical team evaluates off-label romosozumab eligibility in a child under 12. It is intended as an internal clinical decision aid and has not been validated in a published trial.

HealthRX Off-Label Pediatric Romosozumab Eligibility Framework (v1.0)

| Criterion | Minimum Threshold for Consideration | |---|---| | Diagnosis | Confirmed genetic bone fragility disorder (OI type III/IV) or severe secondary osteoporosis (BMD Z-score < negative 3.0) | | Prior therapy | At least 2 years of adequate bisphosphonate therapy without BMD normalization | | Cardiovascular screening | Normal echocardiogram and ECG within 6 months | | Specialist involvement | Pediatric endocrinologist plus metabolic bone disease specialist | | Setting | Academic medical center with IRB oversight | | Consent | Written informed consent from guardians plus assent from child if age-appropriate | | Follow-up plan | DXA every 6 months; fracture log; antiresorptive consolidation plan at 12-month mark |

Dosing Considerations in Children Under 12

No FDA-approved or guideline-endorsed dose exists. Published case data and the active phase-2 trial use a weight-based approach: 2.1 mg/kg subcutaneously once monthly, with a maximum of 210 mg per injection (matching the adult dose). This approach approximates the adult exposure on a per-kilogram basis, though pharmacokinetic studies specific to young children have not been published [6].

Pharmacokinetics: What We Know and Do Not Know

Adult pharmacokinetic data show romosozumab reaches peak serum concentration roughly 5 days after a 210 mg subcutaneous injection, with a terminal half-life of approximately 6.4 days [4]. Clearance in children may differ because renal function per kilogram of body weight is higher in younger patients and because the volume of distribution scaled to body weight may not be linear.

No population pharmacokinetic modeling specific to patients under 12 has been published. The ARCH and FRAME trial populations were exclusively postmenopausal women with a mean age of approximately 71 years [10]. Any extrapolation to a 6-year-old child requires substantial assumptions.

Injection Practicalities

The adult dose is delivered as two 1 mL subcutaneous injections given consecutively at the same visit, typically in the abdomen, upper arm, or thigh. Weight-based pediatric doses below 105 mg would require a single injection with a partial fill. Splitting the 105 mg/mL prefilled syringe for exact weight-based dosing is not described in the prescribing information and would need pharmacy compounding guidance or enrollment in a trial that controls dose preparation [4].

Safety Profile: Adult Data and Pediatric Unknowns

Cardiovascular Risk

The boxed warning in the Evenity prescribing information states: "Romosozumab-aqqg should not be initiated in patients who have had a myocardial infarction or stroke within the preceding year" [4]. In the ARCH trial (N=4,093), cardiovascular serious adverse events occurred in 2.5% of the romosozumab group versus 1.9% of the alendronate group over 33 months, a difference that was statistically significant (P<0.05) [10].

Young children generally carry negligible baseline cardiovascular risk, which may attenuate the absolute risk in this population. Still, the mechanism by which romosozumab may affect cardiovascular tissues is not fully understood. Sclerostin is expressed in vascular smooth muscle cells, and its inhibition could theoretically affect vascular calcification dynamics. No cardiovascular safety data in pediatric patients has been published.

Effects on Growth Plates

This is the concern most specific to children under 12. The growth plate (physis) is regulated partly by Wnt signaling. Preclinical data in juvenile rats showed no adverse effect on longitudinal growth at doses up to 50 mg/kg, which is far above the proposed clinical dose, but rodent physeal biology differs from human in meaningful ways [4]. Monitoring standing height and growth velocity every 3 months during any off-label trial of romosozumab in young children is a minimum precaution.

Hypocalcemia

Romosozumab's anabolic activity creates a transient calcium demand that can precipitate hypocalcemia, particularly in patients with vitamin D insufficiency. The adult prescribing information requires that hypocalcemia be corrected before treatment initiation and that patients receive adequate calcium and vitamin D supplementation [4]. Children with OI often have low baseline serum 25-hydroxyvitamin D levels. Checking 25-OH vitamin D, corrected calcium, and PTH before each monthly injection is standard practice in the case series published to date [6].

Osteonecrosis of the Jaw and Atypical Femoral Fracture

Both adverse effects are associated with antiresorptive agents rather than anabolic agents, but the prescribing information notes they have been reported rarely with romosozumab given its partial antiresorptive effect. In children with growing bones undergoing repeated dental procedures, a baseline dental examination before treatment and prompt reporting of jaw pain or unusual thigh pain during treatment is prudent [4].

Comparison With Other Anabolic Agents in Pediatric Bone Disease

Teriparatide in Children

Teriparatide (PTH 1-34, Forteo) is the other major anabolic bone agent. It carries an FDA boxed warning against use in children and young adults with open growth plates due to osteosarcoma findings in rat studies at high doses administered over most of the animal's lifetime [11]. The osteosarcoma signal in humans has not been confirmed after more than two decades of postmarket surveillance, but the boxed warning has effectively suppressed teriparatide use in the under-12 population.

Romosozumab does not carry an osteosarcoma warning. Preclinical carcinogenicity studies did not produce osteosarcoma findings, which gives it a nominal safety advantage over teriparatide for off-label pediatric consideration, though the evidence base is far smaller [4].

Denosumab in Children

Denosumab (Prolia, 60 mg subcutaneous every 6 months) is used off-label in children with OI and giant cell tumor of bone, with a more substantial pediatric literature than romosozumab. A rebound hypercalcemia phenomenon after denosumab discontinuation has been documented in children and can be severe. This rebound effect is part of the rationale for using denosumab as consolidation therapy after romosozumab in some protocols, with careful tapering rather than abrupt discontinuation [7].

The Endocrine Society's 2023 clinical practice guideline on pediatric bone diseases states: "Evidence supporting anabolic therapy in children with primary bone fragility disorders remains limited; bisphosphonates are the only agents with sufficient evidence to recommend for routine use at this time" [12].

Monitoring Protocol for Any Off-Label Use

Treating a child under 12 with romosozumab outside a registered trial requires a structured monitoring plan. The following parameters represent the minimum standard based on published case data and adult prescribing information.

Before each monthly injection: Serum corrected calcium, serum 25-OH vitamin D, and a brief cardiovascular symptom review.

Every 3 months: Standing height, weight, growth velocity calculation, and fracture log review.

Every 6 months: Lumbar spine and total hip DXA (or whole-body less head in younger children), serum bone turnover markers (P1NP and beta-CTX preferred), and renal function panel.

At 12 months: Full reassessment including peripheral quantitative CT (pQCT) or HR-pQCT if available, decision on antiresorptive consolidation, and cardiovascular review. Romosozumab is given for a maximum of 12 monthly doses, the same limit established in adult trials [4].

Clinical Decision Summary

Romosozumab is not a standard-of-care option for any child under 12. The available evidence consists of fewer than 20 published pediatric cases, nearly all in OI, without control groups or long-term follow-up. Cardiovascular, physeal, and long-term skeletal safety data are absent.

Where romosozumab may be considered in children under 12, the conditions are narrow: confirmed severe bone fragility, documented inadequate response to bisphosphonate therapy of at least 2 years' duration, cardiovascular clearance, specialist oversight, and formal ethics or IRB review. Dosing at 2.1 mg/kg (maximum 210 mg) monthly for 12 months matches the active phase-2 trial protocol. Consolidation with an antiresorptive agent after the 12-month course is recommended by analogy with adult data showing significant bone loss after romosozumab discontinuation without subsequent therapy.

Families and clinicians considering this path should understand that the NCT04857983 trial offers the most appropriate framework for access. Enrollment in a registered trial generates the data needed to either establish or refute a role for romosozumab in pediatric bone disease. Outside a trial, a single-patient expanded access application to the FDA, submitted by the treating physician, is the most legally and ethically defensible route.

At the most recent data cut from the FRAME trial, the adult experience with romosozumab over 12 months showed a 73% reduction in new vertebral fractures versus placebo (N=7,180) [10]. That magnitude of effect in adults with postmenopausal osteoporosis is the biological proof of concept that drives pediatric investigator interest. Whether comparable efficacy translates to a child with OI remains an open question with an ongoing trial answer.