Classification Nuance. The OpenFDA dataset, which draws from the Structured Product Labeling (SPL) files, often includes multiple classification fields, and the specific string "Phosphate Binder [EPC]" may only be assigned to a single product. The other drugs are likely classified using: More Specific Classes: Many of those drugs (like sevelamer, ferric citrate, etc.) may be classified by their specific mechanism or chemical group, which also acts as a phosphate binder. Example: A drug might be classified as "Iron-Containing Compound [EPC]" or "Aluminum-Containing Compound [EPC]" instead of the more general "Phosphate Binder [EPC]". Different Classification Fields: The NDC data contains several classification fields. You might be checking the Established Pharmacological Class (pharm_class_epc), but the other drugs might be listed under: Mechanism of Action (pharm_class_moa), Physiological Effect (pharm_class_pe)