The present Invention provides a dihidropiridazin - 3.5 - dione derivative or a Salt thereof, or a solvate of the compound or Salt, a Pharmaceutical Drug, a Pharmaceutical composition, an inhibitor of sodium dependent phosphate transporter and a Therapeutic agent for Prevention and / or P Ara hyperphosphatemia, secondary hyperparathyroidism and Chronic Kidney Failure.Comprising the compound as an active ingredient, and a method for the Prevention and / or treatment.LA SOLICITUD SE REFIERE A COMPUESTOS DERIVADOS DE DIHIDRO-5-HIDROXI-3-OXO-PIRIDAZIN-4-CARBOXAMIDA SUSTITUIDOS, INHIBIDORES NAPI-IIB Y A SU USO EN EL TRATAMIENTO DE HIPERFOSFATEMIA, HIPERPARATIROIDISMO SECUNDARIO E INSUFICIENCIA RENAL CRÓNICA