AMBTX-01Phase 3, Open-Label Extension Study of AMBTX-01 (Neridronate) for Complex Regional Pain Syndrome Type 1

Inclusion Criteria:

1. Participants must have completed the Week 12 visit of the neridronate AMBTX-01-301 Randomized Clinical Trial (RCT).
2. Both the Investigator and participant must agree that the participant is reasonably likely to benefit from neridronate therapy without undue risk based on information about benefits/risks in the IB.
3. The Investigator must characterize the participants CRPS-1 as a serious condition based on the presence of persistent moderate-to-severe pain or/and persistent moderate-to-severe CRPS-1 signs or/and symptoms other than pain.
4. Participants must be capable of understanding the study requirements and willing to provide informed consent prior to any study-related procedures.
5. Participants must be willing and able to comply with the scheduled treatment plan including 4 infusion visits and safety-related assessments.
6. Participants must have adequate venous access to enable blood sampling and 4 IV infusions.
7. Women of childbearing potential must:

1. Be nonpregnant as determined by a negative highly sensitive urine pregnancy test on every visit before neridronate administration.
2. Be nonlactating.
3. Agree to use a highly effective method of contraception from at least 28 days prior to treatment for oral contraception (or at least 1 week longer than specified by the manufacturer for other contraceptives) and for at least 6 months following last neridronate administration.

Exception: Women exclusively engaging in same sex sexual activities are not required to meet this criterion.

Exclusion Criteria:

1. Individuals who did not participate in AMBTX-01-301 RCT, or those participants from AMBTX-01-301 RCT who discontinued investigational product and/or were withdrawn from the trial.
2. Evidence of severely impaired renal function .
3. Prior or planned renal transplant.
4. The use of any of the following treatments within the timeframe specified from initiation of treatment with neridronate and through the study:

1. Within the last 12 months - IV immunoglobulin, any IV bisphosphonates (excluding investigational product as part of AMBTX-01-301 RCT prior to open-label treatment);
2. Within the last 6 months: Any oral bisphosphonate, denosumab (Prolia®) or receptor activator of nuclear factor kappa B ligand (RANKL) inhibitors (e.g., denosumab biosimilar compounds), Calcitonin, ketamine, Radiation therapy to the head or neck;
3. Within the last 3 months: Cinacalcet, Monoclonal antibody peptides against calcitonin gene-related peptide (CGRP), spinal cord stimulation, radiofrequency ablation, peripheral nerve stimulation and other procedural forms of neuromodulation
4. Within the last 1 month - Any systemic corticosteroid (intranasal, inhaled, or topical corticosteroids are acceptable)
5. Within 2 weeks - Lidocaine infusion, somatic or sympathetic nerve blocks, acupuncture, electromagnetic field treatment, scrambler therapy, dorsal root ganglia (DRG) block, initiation or implementation of radiofrequency ablation or other sympathectomy procedures
5. Hypocalcemia, or high risk for hypocalcemia
6. Vitamin D deficiency
7. Serum potassium or magnesium outside of the laboratory's reference range at Screening
8. Elevated liver-related lab tests or evidence of significant liver disease
9. Significant dental findings.
10. Eye inflammation
11. Clinically unstable cardiac disease