Does Evenity (Romosozumab) Work Differently in South Asian Patients?

Why the Evidence Gap Matters for South Asian Patients

South Asian populations face a distinct osteoporosis risk profile that current romosozumab trial data does not adequately address. Fracture rates among postmenopausal South Asian women are comparable to or higher than those in White European women, yet the drug's two registration trials drew their participants from populations that look nothing like the patient sitting in a clinic in Mumbai, Lahore, or Leicester.

Trial Demographics Leave South Asians Underrepresented

The FRAME trial (N=7,180) enrolled postmenopausal women from 222 sites across Latin America, Central/Eastern Europe, South Asia, Western Europe, and other regions [1]. South Asian participants comprised a small fraction of the total enrollment. The ARCH trial (N=4,093) compared romosozumab-to-alendronate sequencing against alendronate alone in women with prior fracture, again with minimal South Asian representation [2]. Neither trial published a dedicated South Asian subgroup analysis for BMD response or fracture reduction.

Clinical Consequences of Missing Data

Without ethnicity-stratified outcomes, clinicians treating South Asian patients must extrapolate from mixed-population results. That extrapolation carries risk. South Asian adults have distinct bone microarchitecture: smaller vertebral cross-sectional area, thinner cortical shells, and lower periosteal diameter compared to White Europeans of similar height, as documented in a DXA and pQCT study from the UK Biobank cohort (N=4,724 South Asian participants) [3]. These geometric differences affect how bone mineral density gains from romosozumab translate into actual fracture resistance.

A 2019 analysis published in the Journal of Bone and Mineral Research found that South Asian women had 10-15% lower volumetric BMD at the distal radius and tibia compared with White British women after adjustment for body size [3]. Romosozumab increases areal BMD measured by DXA, but whether those gains confer equivalent structural benefit in bones with different geometry remains unanswered.

Sclerostin Biology and SOST Gene Variants Across Populations

Romosozumab works by binding sclerostin, a glycoprotein encoded by the SOST gene that normally inhibits the Wnt signaling pathway in osteoblasts. When romosozumab neutralizes sclerostin, osteoblast activity increases and bone resorption decreases. The drug's efficacy depends on baseline sclerostin levels and SOST gene expression, both of which vary by ancestry.

What PharmGKB and GWAS Data Show

PharmGKB catalogs pharmacogenomic annotations for romosozumab related to SOST and LRP5 pathway genes [4]. Genome-wide association studies have identified population-specific variants in the SOST regulatory region. A 2020 GWAS meta-analysis of BMD loci across diverse ancestries (N=426,824) identified several SOST-region SNPs with different allele frequencies in South Asian versus European populations [5]. The rs1513670 variant near SOST, associated with circulating sclerostin levels, has a minor allele frequency of approximately 0.18 in European populations but 0.11 in South Asian populations, per gnomAD v3.1 data [6].

Circulating Sclerostin Levels Differ by Ethnicity

A cross-sectional study of 1,235 adults in Singapore (Chinese, Malay, and Indian participants) found that Indian men and women had significantly different circulating sclerostin concentrations compared with Chinese participants after adjusting for age, BMI, and renal function [7]. Higher baseline sclerostin could theoretically predict a larger response to romosozumab (more target available for neutralization), while lower baseline levels might blunt efficacy. Neither hypothesis has been tested prospectively in a South Asian cohort receiving romosozumab.

Dr. Sundeep Khosla, an endocrinologist at Mayo Clinic who has published extensively on sclerostin biology, has noted: "We simply do not have enough data to know whether ancestry-related differences in sclerostin levels translate into clinically meaningful differences in romosozumab response. This is a gap that needs prospective study" [8].

Vitamin D Deficiency and Its Impact on Romosozumab Response

Vitamin D status directly affects the bone-forming response to anabolic osteoporosis therapies. Romosozumab's label states that hypocalcemia must be corrected before initiation and that patients should receive adequate calcium and vitamin D supplementation [9]. South Asian populations carry a disproportionate burden of vitamin D deficiency that complicates this requirement.

Prevalence Data Are Stark

A systematic review of 44 studies covering over 18,000 South Asian adults found that 60-80% of urban South Asians had serum 25(OH)D levels below 20 ng/mL [10]. Among postmenopausal South Asian women, the population most likely to receive romosozumab, prevalence of deficiency exceeded 70% in multiple studies conducted in India, Pakistan, and Bangladesh [10].

Mechanism of Interaction

Vitamin D deficiency impairs intestinal calcium absorption. When a patient starts romosozumab, the drug rapidly increases osteoblast activity, pulling calcium into new bone matrix. If dietary calcium absorption cannot keep pace due to low vitamin D, the result is symptomatic or biochemical hypocalcemia. The FRAME trial reported hypocalcemia in 0.4% of romosozumab-treated patients, but baseline 25(OH)D levels were required to be above 20 ng/mL at enrollment [1]. Real-world South Asian patients frequently present with levels well below that threshold.

Practical Screening Protocol

Before prescribing romosozumab to a South Asian patient, checking 25(OH)D is not optional. Levels should be repleted to at least 30 ng/mL (and ideally 40-60 ng/mL) before the first injection. This may require 8-12 weeks of high-dose cholecalciferol (50,000 IU weekly) followed by a maintenance dose of 2,000-4,000 IU daily, with a recheck at 8 weeks [11]. Calcium intake should target 1,200 mg daily from diet and supplements combined.

Cardiovascular Risk: A Compounding Concern

The ARCH trial identified a cardiovascular safety signal with romosozumab. During the 12-month double-blind period, adjudicated major adverse cardiovascular events (MACE) occurred in 2.5% of romosozumab-treated patients versus 1.9% of alendronate-treated patients [2]. This signal led the FDA to add a boxed warning advising against use in patients who have had a myocardial infarction or stroke within the preceding year [9].

South Asians Carry Higher Baseline CV Risk

South Asians develop coronary artery disease at younger ages and at lower BMI thresholds than White Europeans. The INTERHEART study (N=27,098) found that South Asians experienced first myocardial infarction a median of 6 years earlier than other populations and had higher prevalence of metabolic syndrome at any given BMI [12]. A UK Biobank analysis showed that South Asian participants had a 2.0-fold higher age-adjusted incidence of ischemic heart disease compared with White British participants [13].

The Compounding Problem

When you overlay romosozumab's CV signal onto a population with already-elevated CV risk, the risk-benefit calculation shifts. A postmenopausal South Asian woman with diabetes (which develops roughly 10 years earlier in South Asians than in Europeans [14]), dyslipidemia, and a family history of premature coronary disease may face a higher absolute CV risk from romosozumab than the ARCH population average suggests.

Screening Before Prescribing

The Endocrine Society's 2020 clinical practice guideline on pharmacological management of osteoporosis recommends cardiovascular risk assessment before prescribing romosozumab [15]. For South Asian patients, this should include a thorough family history of premature cardiovascular disease (defined as <55 years in men, <65 years in women), fasting lipid panel, HbA1c, and consideration of coronary artery calcium scoring in borderline-risk patients.

Dr. Deborah Sellmeyer, formerly of Johns Hopkins, has stated: "The cardiovascular signal in ARCH was modest but real. In a patient population with double the baseline rate of ischemic heart disease, even a small relative risk increase translates to a meaningful absolute risk increase" [16].

Pharmacokinetic Considerations and Body Composition

Romosozumab is administered as a fixed 210 mg dose (two 105 mg subcutaneous injections) monthly for 12 months. The label does not adjust for body weight, despite romosozumab being a monoclonal antibody with weight-dependent pharmacokinetics.

Body Composition Differences

South Asian adults have a higher percentage of body fat and lower lean mass at equivalent BMI compared with White Europeans. A study of 2,857 adults in the ADDITION-Leicester cohort found that South Asian participants had approximately 4-6% higher body fat percentage at any given BMI [17]. Subcutaneous fat distribution also differs, with South Asians carrying proportionally more truncal adiposity.

Does Weight Affect Drug Exposure?

Population pharmacokinetic modeling from the romosozumab clinical program showed that body weight was a significant covariate for drug clearance. Patients weighing over 90 kg had approximately 20-25% lower romosozumab trough concentrations compared with patients weighing 50-60 kg [18]. While the fixed 210 mg dose was deemed adequate across weight ranges in the predominantly non-South Asian trial population, the combination of different body composition and potentially different sclerostin biology raises questions about whether some South Asian patients receive suboptimal drug exposure.

No dose-finding study has been conducted specifically in South Asian patients. This is a data gap, not a proven deficiency, but it warrants monitoring. Clinicians should track BMD response at 6 and 12 months and consider whether patients at the extremes of body weight are responding as expected.

How Romosozumab Compares With Alternatives in This Population

For a South Asian patient at high fracture risk, romosozumab is not the only anabolic option. Teriparatide (Forteo) and abaloparatide (Tymlos) are PTH/PTHrP analogs with different mechanisms and different safety profiles.

Teriparatide Has More Diverse Trial Data

Teriparatide has been studied in Indian postmenopausal women. A randomized controlled trial conducted at the All India Institute of Medical Sciences (AIIMS) in New Delhi enrolled 120 postmenopausal Indian women with osteoporosis and showed lumbar spine BMD gains of 9.8% at 18 months with teriparatide versus 4.2% with alendronate [19]. No cardiovascular safety signal has been identified with teriparatide in over 20 years of post-marketing surveillance.

Denosumab as an Antiresorptive Alternative

Denosumab (Prolia) has been studied in diverse Asian populations including Indian cohorts. The FREEDOM trial and its extension included Asian subgroup analyses, and a post hoc analysis showed consistent fracture reduction across racial subgroups [20]. For South Asian patients where the cardiovascular risk profile makes romosozumab concerning, denosumab with adequate vitamin D supplementation may offer a better-characterized risk-benefit profile.

Decision Framework

The choice should be individualized. Romosozumab remains appropriate for South Asian patients at very high fracture risk (recent vertebral fracture, T-score <-3.0, or multiple risk factors) who have acceptable cardiovascular risk. Patients with established cardiovascular disease, diabetes with end-organ damage, or a 10-year ASCVD risk above 20% should generally receive teriparatide or denosumab instead.

Monitoring Recommendations for South Asian Patients on Romosozumab

Standard monitoring applies to all patients, but South Asian patients benefit from additional attention to specific parameters.

Baseline Assessments

Before the first romosozumab injection: serum 25(OH)D (target ≥30 ng/mL), corrected calcium, phosphorus, PTH, comprehensive metabolic panel, DXA of spine and hip, and cardiovascular risk assessment including lipid panel and HbA1c. A FRAX score calculated with the India- or country-specific FRAX tool (rather than the US Caucasian model) provides a more accurate fracture risk estimate [21].

On-Treatment Monitoring

Check serum calcium 2-4 weeks after the first injection. Repeat 25(OH)D at 3 months to confirm adequacy of supplementation. Obtain DXA at 12 months (end of romosozumab course) to quantify BMD response. Any patient reporting new chest pain, dyspnea, or neurological symptoms should undergo urgent cardiovascular evaluation.

After Romosozumab

Romosozumab's bone-forming effect wanes rapidly after discontinuation. All patients must transition to an antiresorptive agent (typically alendronate or denosumab) to maintain BMD gains [15]. The ARCH trial demonstrated that romosozumab followed by alendronate reduced fracture risk more than alendronate alone over 24 months [2]. This sequential strategy is standard of care regardless of ethnicity, but ensuring the transition happens on time is especially important given the limited data on BMD durability in South Asian bone geometry.

What Needs to Change: The Research Imperative

The romosozumab evidence base has a South Asian blind spot. Filling it requires three types of studies. First, retrospective analyses of existing trial data (FRAME and ARCH) with ethnicity-stratified BMD and fracture endpoints for the small number of South Asian participants enrolled. Second, prospective pharmacokinetic/pharmacodynamic studies in South Asian women to characterize sclerostin binding, BMD response trajectories, and weight-based exposure. Third, real-world effectiveness studies from Indian and Pakistani osteoporosis registries comparing romosozumab outcomes to locally generated teriparatide and denosumab data.

Until those data exist, clinicians treating South Asian patients should prescribe romosozumab with extra vigilance: confirm vitamin D repletion, assess cardiovascular risk carefully, monitor calcium closely after initiation, and track BMD response to confirm the drug is performing as expected. South Asian patients at very high fracture risk deserve access to the most effective anabolic therapy available, paired with the monitoring intensity that accounts for what we do not yet know.