What was the primary endpoint of the ARCH trial?

New vertebral fracture incidence at 24 months, assessed by central radiographic evaluation. Romosozumab-to-alendronate reduced this by 48% compared with alendronate alone.

How does ARCH differ from the FRAME trial?

FRAME compared romosozumab to placebo. ARCH compared romosozumab to an active comparator (alendronate), a much harder bar. ARCH also enrolled higher-risk patients with prevalent fractures, making its results more relevant to severe osteoporosis.

Why does romosozumab have a cardiovascular warning?

ARCH found a numerical excess of serious cardiovascular events (2.5% vs 1.9%) in the romosozumab arm during the 12-month treatment period. The FDA added a boxed warning contraindicating romosozumab in patients with MI or stroke within the prior year.

Who is eligible for romosozumab based on ARCH data?

Postmenopausal women at very high fracture risk: those with prior fragility fracture, T-score below -2.5, or fracture despite existing therapy. Patients with recent cardiovascular events are excluded per the label.

Does romosozumab work in men?

The BRIDGE trial showed BMD gains in men. The FDA label includes a male indication, but ARCH enrolled only women. Direct fracture reduction data in men from an active-comparator trial are not available.

How long can you take romosozumab?

The approved course is 12 monthly doses. The anabolic effect wanes after stopping, so transition to an antiresorptive (bisphosphonate or denosumab) is required to maintain gains.

What happens if you skip the antiresorptive after romosozumab?

BMD gains erode. ARCH demonstrated sustained benefit specifically because patients transitioned to alendronate. Without antiresorptive follow-up, the bone formed during the anabolic phase is progressively resorbed.

Has ARCH changed first-line osteoporosis treatment?

For very high-risk patients, yes. AACE, the Endocrine Society, and international bodies now recommend considering anabolic-first therapy. For average-risk osteoporosis, bisphosphonates remain first-line.

How much does a course of romosozumab cost?

Approximately $22,000 for 12 monthly injections at US list price. Most insurers require prior authorization with documentation of high fracture risk or bisphosphonate failure.

Can romosozumab be used for glucocorticoid-induced osteoporosis?

There is no large RCT specifically studying romosozumab in glucocorticoid-induced osteoporosis. The mechanism is theoretically suited to this population, but evidence remains limited to small studies.

What ARCH Actually Changes in Clinical Practice

By HealthRX Medical Team

Published May 25, 2026Updated May 25, 2026Last reviewed May 25, 2026

At a glance

| Field | Detail | |---|---| | Trial name | ARCH (Active-Controlled Fracture Study in Postmenopausal Women with Osteoporosis at High Risk) | | N | 4,093 | | Intervention | Romosozumab 210 mg SC monthly x 12 months, then alendronate 70 mg weekly | | Comparator | Alendronate 70 mg weekly throughout | | Duration | Median 33 months | | Primary endpoint | New vertebral fracture at 24 months | | Key result | 48% relative risk reduction in new vertebral fractures vs alendronate (6.2% vs 11.9%; p < 0.001) |

Why ARCH Mattered More Than FRAME

Before ARCH, the FRAME trial had already shown romosozumab beat placebo for vertebral fracture reduction. That result was necessary but insufficient. Clinicians treating severe osteoporosis were not choosing between romosozumab and nothing. They were choosing between romosozumab and a bisphosphonate they already trusted. ARCH answered the harder question: does the sclerostin inhibitor beat a proven active comparator?

The answer was yes, and it was not close. At 24 months, romosozumab-to-alendronate reduced new vertebral fractures by 48% compared with alendronate alone (6.2% vs 11.9%; p < 0.001). Clinical vertebral fractures dropped by 27% over the full study period. Nonvertebral fractures fell by 19%, and hip fractures by 38%, though the hip fracture reduction did not reach statistical significance until a later analysis window.

These are active-comparator numbers. A 48% relative risk reduction over a drug that already works is a different clinical signal than beating placebo.

Methodology Worth Knowing

The Population Was Not Average Osteoporosis

ARCH enrolled postmenopausal women aged 55 to 90 with a T-score of -2.5 or lower at the total hip or femoral neck, plus at least one moderate or severe vertebral fracture, or two or more mild vertebral fractures. The mean age was 74. Over 96% had a prior vertebral fracture at baseline.

This is a critical detail. ARCH was not testing romosozumab in early osteoporosis. The trial population had established disease with fracture history. Clinicians who extrapolate ARCH results to low-risk patients are applying data from a population that does not match.

Open-Label Phase, Blinded Assessment

The double-blind period lasted 12 months (romosozumab vs alendronate). After month 12, all patients received open-label alendronate. Vertebral fracture assessment used central radiographic reading by evaluators blinded to treatment assignment. This design means the 24-month vertebral fracture endpoint combined a blinded treatment phase with an open-label antiresorptive continuation, which is relevant to interpretation.

The Sequencing Design Was the Real Innovation

ARCH was not simply romosozumab vs alendronate. It was romosozumab-then-alendronate vs alendronate-alone. This "build then maintain" architecture reflected growing evidence that anabolic agents produce the greatest BMD gains when followed by antiresorptive therapy, while starting with antiresorptives may blunt subsequent anabolic response. The trial tested a treatment sequence, not a drug in isolation.

Full Results Beyond the Headline

| Outcome | Romosozumab → Alendronate | Alendronate Alone | Relative Risk Reduction | p-value | |---|---|---|---|---| | New vertebral fracture (24 mo) | 6.2% | 11.9% | 48% | < 0.001 | | Clinical fracture (full period) | 9.7% | 13.0% | 27% | < 0.001 | | Nonvertebral fracture (full period) | 8.7% | 10.6% | 19% | 0.04 | | Hip fracture (full period) | 2.0% | 3.2% | 38% | 0.02 |

BMD gains at 12 months (romosozumab phase) were substantial: total hip BMD increased by 2.9% in the romosozumab group vs 0.5% with alendronate. Lumbar spine gains were even larger. After the switch to alendronate in both groups, BMD differences were maintained but did not widen further.

The Kaplan-Meier curves for clinical fracture separated early, within the first 12 months, and stayed apart. This rapid onset of fracture protection is clinically meaningful for patients at imminent fracture risk.

The Cardiovascular Signal That Complicated Everything

ARCH found a numerical imbalance in adjudicated serious cardiovascular events: 2.5% in the romosozumab group vs 1.9% in the alendronate group during the 12-month double-blind period. This was not a prespecified endpoint and did not reach statistical significance, but it was enough to reshape regulatory decisions.

The FDA approved romosozumab (Evenity) in April 2019 with a boxed warning about potential cardiovascular risk, contraindicating use in patients who have had a myocardial infarction or stroke within the preceding year. The European Medicines Agency added similar restrictions. Japan and other markets approved without the boxed warning but included cardiovascular cautions.

Context matters here. FRAME, which compared romosozumab to placebo, did not show this cardiovascular signal. One interpretation: alendronate may be mildly cardioprotective, making the comparator group appear safer rather than romosozumab appearing harmful. A post hoc analysis published in the Journal of Bone and Mineral Research examined pooled cardiovascular data across romosozumab trials without finding a consistent dose-response or mechanistic signal.

Regardless of mechanism, the boxed warning changed prescribing behavior. Many clinicians perform a basic cardiovascular risk screen before prescribing romosozumab. Patients with recent MI or stroke are excluded. This practical filter narrows the eligible population meaningfully.

What Actually Changed in Guidelines

AACE/ACE 2020 Updated Algorithm

The American Association of Clinical Endocrinology updated its osteoporosis guidelines to recommend anabolic-first therapy (romosozumab, teriparatide, or abaloparatide) for patients at very high fracture risk. "Very high risk" was defined as recent fracture within 24 months, fractures while on approved therapy, multiple fractures, fractures while on drugs causing skeletal harm (glucocorticoids), very low T-score (< -3.0), high fall risk, or very high FRAX probability.

Before ARCH, the default was to start with bisphosphonates and escalate to anabolics if patients fractured through therapy. ARCH and parallel data from teriparatide sequencing studies (VERO) flipped this. For high-risk patients, starting anabolic and stepping down to antiresorptive became the preferred sequence.

Endocrine Society 2020 Guidelines

The Endocrine Society clinical practice guideline similarly recommended considering romosozumab as initial therapy in postmenopausal women at very high fracture risk, explicitly citing ARCH as supporting evidence for the anabolic-first approach.

NOGG (UK) and IOF Positions

The UK National Osteoporosis Guideline Group and International Osteoporosis Foundation both incorporated anabolic-first recommendations for very high-risk patients. The speed of guideline uptake was unusual for osteoporosis, a field where practice change typically lags evidence by years.

Prescribing Patterns: What Shifted and What Did Not

Despite guideline updates, romosozumab uptake has been slower than the evidence might predict. Several practical barriers explain the gap.

Cost. Romosozumab carries a list price around $1,825 per monthly injection in the US. A 12-month course costs approximately $22,000 before insurance. Many payers require prior authorization demonstrating bisphosphonate failure or very high fracture risk. This creates an access bottleneck that keeps bisphosphonates as the de facto first-line for most patients.

Administration. Monthly subcutaneous injection at a healthcare facility (two prefilled syringes per dose) is more burdensome than a weekly oral bisphosphonate. Patients must attend 12 consecutive monthly visits during the anabolic phase.

Cardiovascular screening. The boxed warning adds a required assessment step. Clinicians in primary care, where most osteoporosis is managed, may be less comfortable navigating the cardiovascular risk calculus.

Duration limit. The Evenity prescribing information limits use to 12 monthly doses. The effect of romosozumab wanes after discontinuation without antiresorptive follow-up. This obligatory two-phase treatment plan requires longitudinal coordination that some clinical settings struggle to maintain.

The result: romosozumab is used mostly by endocrinologists and rheumatologists treating patients who meet very high-risk criteria. Primary care prescribing remains minimal. Bisphosphonates still dominate initial osteoporosis prescriptions by a wide margin.

What ARCH Does Not Tell You

Men. ARCH enrolled only postmenopausal women. The FDA label includes an indication for men at high fracture risk based on the smaller BRIDGE trial, but ARCH data cannot be directly applied to male osteoporosis.

Glucocorticoid-induced osteoporosis. Patients on chronic glucocorticoids were not specifically studied. The mechanism of glucocorticoid bone loss (primarily suppressed formation) makes romosozumab theoretically appealing here, but trial evidence for this population remains limited.

Retreatment. ARCH provided one 12-month course. Whether a second course years later restores the initial anabolic response is unknown from controlled data. Small open-label studies suggest partial efficacy on retreatment.

Long-term cardiovascular outcomes. The cardiovascular signal in ARCH was detected during a 12-month exposure. Whether the risk persists, accumulates, or resolves after stopping romosozumab is not established.

Treatment-naive patients with moderate risk. ARCH enrolled patients with prevalent fractures and very low BMD. The trial does not support starting romosozumab in a 60-year-old with a T-score of -2.6 and no fracture history. That patient was not in ARCH.

The Bottom Line for Clinical Practice in 2026

ARCH established that the sequence matters. For postmenopausal women at very high fracture risk, building bone with romosozumab first and maintaining with a bisphosphonate second produces better fracture outcomes than starting and staying on a bisphosphonate. This principle, anabolic before antiresorptive, is now embedded in major society guidelines.

The practical impact is narrower than the evidence might justify. Cost, access, the cardiovascular boxed warning, and the complexity of a two-phase treatment sequence have limited romosozumab to a fraction of the patients who might benefit. Clinicians should use ARCH as the basis for a specific conversation with specific patients: those with recent fracture, very low BMD, or fracture despite bisphosphonate therapy. For those patients, the data support starting with romosozumab rather than waiting for a second fracture to justify escalation.

Frequently asked questions

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References

Saag KG, Petersen J, Brandi ML, et al. Romosozumab or alendronate for fracture prevention in women with osteoporosis. N Engl J Med. 2017;377(15):1417-1427. PubMed
US FDA. Evenity (romosozumab-aqqg) prescribing information. April 2019. FDA Label
Camacho PM, Petak SM, Binkley N, et al. American Association of Clinical Endocrinologists/American College of Endocrinology clinical practice guidelines for the diagnosis and treatment of postmenopausal osteoporosis, 2020 update. Endocr Pract. 2020;26(Suppl 1):1-46. PubMed
Shoback D, Rosen CJ, Black DM, et al. Pharmacological management of osteoporosis in postmenopausal women: an Endocrine Society guideline update. J Clin Endocrinol Metab. 2020;105(3):dgaa048. PubMed
Cummings SR, Cosman F, Lewiecki EM, et al. Goal-directed treatment for osteoporosis: a progress report from the ASBMR-NOF Working Group on goal-directed treatment for osteoporosis. J Bone Miner Res. 2017;32(1):3-10. PubMed