SCIENTIFIC DOCUMENTATION · NERIDRONATE
Does neridronate
work in CRPS-I?
The clinical literature provides direct evidence that neridronate can produce clinically meaningful benefit in appropriately selected patients with CRPS-I. Two multicenter, randomized, double-blind, placebo-controlled trials found neridronate superior to placebo for pain and several CRPS-related clinical outcomes.
Long-term extension and real-world studies also report sustained improvement, especially when treatment is given in the early phase of CRPS-I. The evidence is strongest for early or acute CRPS-I and should not be interpreted as a guarantee that every person with CRPS will respond.
THE EVIDENCE IN ONE VIEW
PLACEBO-CONTROLLED
2013 IV RCT
−46.5 mm
mean VAS change at day 40 with neridronate vs −22.6 mm with placebo
2021 IM RCT
65.9%
achieved ≥50% pain reduction vs 29.7% with placebo at day 30
2022 FOLLOW-UP
91.4%
IM-treated completers were ≥50% pain responders at one year
01
These numbers come from different studies and time points. They should be read in the context of each study population and protocol.
WHAT DOES “IT WORKS” MEAN SCIENTIFICALLY?
It means the drug performed better than placebo on predefined clinical outcomes.
Scientific efficacy is not established by testimonials alone. The strongest evidence comes from controlled trials in which patients are randomly assigned to active treatment or placebo and outcomes are measured using the same rules in both groups.
01
Pain decreased more than with placebo
Both randomized neridronate trials found statistically significant superiority over placebo for the principal pain outcomes.
02
More patients reached a major pain response
In the 2021 trial, 65.9% of neridronate-treated patients achieved at least a 50% reduction in pain compared with 29.7% receiving placebo.
03
CRPS signs improved too
The studies reported improvements in findings such as allodynia, hyperalgesia, edema and pain on passive movement—not only a change in a single pain score.
04
Benefit continued after treatment
Extension studies reported persistent or further improvement over the following months, supporting an effect that outlasted the short administration period.
EVIDENCE HIERARCHY
Not one study. Multiple layers of clinical evidence.
01
Randomized IV trial vs placebo
02
Randomized IM trial vs placebo
03
Prespecified 12-month extension
04
Multi-year real-world observational data
05
Italian regulatory approval for CRPS
RANDOMIZED TRIAL · RHEUMATOLOGY · 2013
The pivotal IV neridronate study
82 patients
Multicenter
Double-blind
Placebo-controlled
Varenna et al. tested 400 mg total IV neridronate against placebo.
Eighty-two patients with CRPS-I affecting the hand or foot were randomized to receive four intravenous infusions of 100 mg neridronate over 10 days or placebo. After the blinded phase, the former placebo group received the same neridronate regimen.
01
100 mg IV × 4
Four infusions over a 10-day period.
02
Randomized against placebo
The initial efficacy comparison was blinded and placebo controlled.
03
Open extension
The placebo group later received neridronate, providing an additional within-study observation.
PRIMARY CLINICAL SIGNAL
P < 0.0001
Pain reduction was substantially greater with neridronate.
Neridronate · −46.5 mm
Mean VAS change at day 40
Placebo · −22.6 mm
Same day-40 comparison
The study also found significant improvements in additional pain and quality-of-life indices compared with placebo.
WHAT HAPPENED NEXT?
When the former placebo group later received neridronate, the investigators reported a response pattern comparable to the group that had received active treatment during the blinded phase.
04
ONE-YEAR OBSERVATION REPORTED IN THE ORIGINAL STUDY
At one year, the investigators reported that none of the study patients was referring symptoms linked to CRPS-I.
This is an important result from this particular study population. It should be reported as the investigators’ follow-up finding—not converted into a claim that every patient with CRPS-I will achieve the same outcome.
INDEPENDENT RANDOMIZED CONFIRMATION · 2021
A second placebo-controlled trial reproduced the clinical signal.
78 patients
Multicenter
Double-blind
IM route
NERIDRONATE
65.9%
≥50% reduction in pain
27 of 41 patients reached the prespecified responder threshold at day 30.
p = 0.0017 vs placebo
PLACEBO
29.7%
≥50% reduction in pain
11 of 37 patients reached the same responder threshold at day 30.
Same outcome definition
TREATMENT DIFFERENCE
+36.1%
More responders
The reported difference in responder rate was 36.1 percentage points.
95% CI 14.01%–55.7%
THE EFFECT WAS NOT LIMITED TO THE VAS SCORE
Several physical signs of CRPS improved more with neridronate than with placebo.
01
Allodynia
Present at day 30 in 20% of neridronate patients vs 63.3% of placebo patients.
02
Hyperalgesia
Present at day 30 in 20% vs 56.7%, respectively.
03
Edema
The edema score improved significantly more in the neridronate group.
04
Pain on passive motion
The motion-pain score also improved significantly more than with placebo.
The 2021 investigators concluded that intramuscular neridronate produced a clinically relevant benefit compared with placebo in patients with acute CRPS-I.
12-MONTH EXTENSION STUDY · 2022
Did the benefit disappear after the treatment ended?
In the prespecified open-label extension, patients previously treated with intramuscular neridronate and former placebo patients subsequently treated with IV neridronate were followed for one year.
01
91.4%
IM group responders at day 360
32 of 35 study completers had a pain reduction of at least 50% at one year.
02
96.3%
Early IM responders remained responders
26 of the 27 patients who were responders at the end of the blinded phase remained responders at day 360.
03
88%
IV group responders at day 360
22 of 25 IV-treated study completers met the same ≥50% pain reduction threshold.
WHAT THE AUTHORS REPORTED
Pain, clinical and functional measures were maintained and further improved over 12 months in most patients.
This extension was open label and included only patients continuing into follow-up, so it does not have the same evidentiary strength as the blinded placebo comparison. It does, however, provide important information about durability in the followed cohort.
REAL-WORLD EVIDENCE · 2024
Long-term clinical practice data point in the same direction—especially with early treatment.
Observational studies cannot prove efficacy as strongly as randomized trials because there is no concurrent placebo group. They can, however, show what happened to treated patients over longer periods in routine clinical practice.
UPPER-LIMB CRPS-I COHORT
49
patients treated with IV neridronate
MEAN FOLLOW-UP
4 years
47.7 ± 22.0 months
DIAGNOSTIC RESOLUTION
93.9%
46 of 49 no longer met CRPS diagnostic criteria at follow-up
NO FUNCTIONAL LIMITATION
77.6%
38 of 49 were free of functional limitations by the study’s DASH threshold
01
THE TIMING SIGNAL
Delay between disease onset and treatment predicted more residual disability.
In the 2024 real-world upper-limb cohort, the authors identified treatment delay as a predictor of residual functional limitation. The study conclusion emphasized full recovery in more than three quarters of patients when treated early.
WHY THIS EVIDENCE MATTERS
The conclusion does not depend on patient testimonials alone.
Testimonials can describe an individual experience but cannot show whether improvement was caused by the treatment. Randomization, placebo control, predefined outcomes and statistical comparison are designed to answer that question more rigorously.
01
Randomized
Patients were assigned to active treatment or placebo rather than choosing their group.
02
Double-blind
The randomized trials were designed to reduce expectation and observer bias.
03
Placebo-controlled
Neridronate was compared against the change occurring in patients receiving placebo.
04
Multicenter
The randomized studies involved multiple clinical centers rather than a single physician’s experience.
05
Clinically meaningful threshold
The 2021 trial predefined a ≥50% reduction in pain as an important responder endpoint.
06
Replication
A later randomized study using a different parenteral route again found superiority over placebo.
REGULATORY CONTEXT · AUGUST 2026
Approved in Italy. Still investigational for CRPS in the United States.
Regulatory status is different from scientific efficacy. Neridronate is approved and marketed in Italy for CRPS. In the United States, it does not yet have FDA marketing approval for CRPS and is being studied in a pivotal Phase 3 program.
ITALY
Approved for CRPS
Abiogen Pharma states that Italian approval for CRPS was based on safety and efficacy demonstrated in two Phase 3 clinical studies.
UNITED STATES
Pivotal Phase 3 underway
Ambros Therapeutics announced the first patient dosed in CRPS-RISE in June 2026. The approximately 270-patient trial compares four IV neridronate infusions with placebo in selected warm CRPS-I patients.
FDA DESIGNATIONS
Breakthrough Therapy · Fast Track · Orphan Drug
These designations support and accelerate development. They are important regulatory signals, but they are not equivalent to FDA marketing approval.
READ THE EVIDENCE PRECISELY
Strong evidence of efficacy is not the same as a universal guarantee.
A scientific page is more credible when it states both what the evidence supports and where the boundaries of that evidence are.
01
The randomized evidence is strongest in CRPS-I
The pivotal neridronate studies enrolled patients with CRPS type 1, not every form of CRPS.
02
Early disease is especially represented
The 2021 trial enrolled acute CRPS-I, and later observational data reinforce the importance of treatment timing.
03
Not every patient was a responder
Placebo-controlled trials show probability of benefit—not certainty for an individual patient.
04
Long-term extensions are not placebo-controlled for the full follow-up
They are useful for durability, but they carry more potential bias than the initial randomized comparisons.
05
Class-level reviews remain cautious
Recent evidence syntheses of bisphosphonates as a class support short-term pain reduction but note heterogeneity and uncertainty around medium- and long-term effects across studies.
06
The correct conclusion
Neridronate has demonstrated efficacy in randomized CRPS-I trials. Individual suitability and expected response still require clinical assessment.
THE SCIENTIFIC BOTTOM LINE
Neridronate has demonstrated efficacy in CRPS-I in randomized, placebo-controlled clinical trials.
The strongest defensible statement is not “neridronate works for everyone.” It is that controlled trials demonstrated clinically relevant superiority to placebo, later follow-up showed sustained benefit in the observed cohorts, and real-world studies are consistent with favorable long-term outcomes when CRPS-I is treated early.
COMMON QUESTIONS
How to interpret the neridronate evidence
Yes. Two multicenter randomized, double-blind, placebo-controlled studies reported statistically significant superiority of neridronate over placebo on pain outcomes. The 2013 study used IV treatment; the 2021 study used intramuscular treatment.
At day 30, 65.9% of neridronate-treated patients achieved at least a 50% reduction in VAS pain compared with 29.7% of placebo-treated patients. The between-group responder difference was statistically significant.
No. The randomized studies also reported improvements in several clinical signs, including allodynia, hyperalgesia, edema and pain with movement. Long-term studies also evaluated functional outcomes.
No. Clinical trials estimate treatment effects in defined populations. The strongest neridronate evidence applies to CRPS-I, particularly relatively early disease. Individual response can differ.
Drug approval is jurisdiction-specific. Neridronate is approved for CRPS in Italy. In the United States, a new pivotal Phase 3 study is underway to support a potential FDA regulatory submission. FDA Breakthrough Therapy, Fast Track and Orphan Drug designations do not themselves constitute marketing approval.
PATIENT SUPPORT
Bring the study—not just the claim—to your medical discussion.
Carla Crowe, Patient Care Coordinator – California, can help patients locate CRPS Support resources, organize questions and understand practical information about treatment in Italy. Clinical suitability for neridronate must be assessed by qualified healthcare professionals.
CARLA CROWE
Patient Care Coordinator – California
CORE SCIENTIFIC SOURCES
The evidence is available to read directly.
This page prioritizes original randomized studies, long-term follow-up, observational research and current regulatory documentation.
RHEUMATOLOGY · 2013
Varenna et al. — IV randomized trial
82-patient multicenter, double-blind, placebo-controlled CRPS-I study.
THER ADV MUSCULOSKELET DIS · 2021
Varenna et al. — IM randomized trial
78-patient multicenter, double-blind, placebo-controlled study.
THER ADV MUSCULOSKELET DIS · 2022
One-year extension
Prespecified follow-up evaluating durability after parenteral neridronate.
CLIN MED INSIGHTS · 2024
Long-term real-world study
Upper-limb CRPS-I cohort with mean follow-up of approximately four years.
TCRM · 2013
Clinical development review
Review of neridronate development including the pivotal CRPS-I findings.
ANNALS · 2026
Bisphosphonate systematic review
Independent class-level review supporting short-term pain reduction while highlighting heterogeneity and longer-term uncertainty.
AMBROS · 2026
Current U.S. Phase 3 program
CRPS-RISE pivotal randomized trial and current FDA-development status.
ABIOGEN · 2025
Italian approval documentation
Current company documentation confirming Italian CRPS approval and the two Phase 3 studies.
Scientific and regulatory information reviewed for this page: August 2026.
THE CLAIM SHOULD BE AS STRONG AS THE EVIDENCE—AND NO STRONGER.