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

Inclusion Criteria

• Participants must have completed the Week 12 visit of the neridronate AMBTX-01-301 Randomized Clinical Trial (RCT).
• 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.
• 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.
• Participants must be capable of understanding the study requirements and willing to provide informed consent prior to any study-related procedures.
• Participants must be willing and able to comply with the scheduled treatment plan including 4 infusion visits and safety-related assessments.
• Participants must have adequate venous access to enable blood sampling and 4 IV infusions.
• Women of childbearing potential must:

• Be nonpregnant as determined by a negative highly sensitive urine pregnancy test on every visit before neridronate administration.
• Be nonlactating.
• 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

• 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in AMBTX-01-301 RCT, or those participants from AMBTX-01-301 RCT who discontinued investigational product and/or were withdrawn from the trial.
• Evidence of severely impaired renal function .
• Prior or planned renal transplant.
• The use of any of the following treatments within the timeframe specified from initiation of treatment with neridronate and through the study:

• 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);
• 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;
• 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
• Within the last 1 month - Any systemic corticosteroid (intranasal, inhaled, or topical corticosteroids are acceptable)
• 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
• Hypocalcemia, or high risk for hypocalcemia
• Vitamin D deficiency
• Serum potassium or magnesium outside of the laboratory's reference range at Screening
• Elevated liver-related lab tests or evidence of significant liver disease
• Significant dental findings.
• Eye inflammation
• Clinically unstable cardiac disease