Dose Optimization and Efficacy Assessment of a Fluoropyrimidine Antidote

Inclusion Criteria: Presence of at least one severe toxicity or intoxication resulting from fluoropyrimidine use, defined as: receiving an overdose of medication (total dose and/or infusion rate higher than recommended in the package insert) and/or Grade 3 or 4 serious adverse events after fluoropyrimidine exposure, according to CTCAE v5.0, which may include (but are not limited to): nausea, vomiting, diarrhea, anemia, neutropenia, febrile neutropenia, thrombocytopenia, and mucositis; Lack of access to uridine triacetate (UT) in the standard of care; Diagnosis of an invasive solid tumor under systemic treatment with a fluoropyrimidine (5-fluorouracil or capecitabine); Organ function considered adequate by the investigator prior to the current fluoropyrimidine intoxication episode; Ability to take oral medication; For men and women of reproductive potential, agreement to practice abstinence or use highly effective contraceptive methods during study participation and for at least 6 months after the last dose of IP; Men must agree not to donate sperm for at least 6 months after the last dose of IP; Body surface area between 1.4 and 2.4 m², calculated using the Du Bois method; AST/ALT within normal limits for participants without liver metastases; AST/ALT up to 3x the upper limit of normal in participants with liver metastases; Total and fractionated bilirubin up to 2x the upper limit of normal; Agreement to abstain from alcohol consumption during the treatment period; As a specific inclusion criterion for participants in Phase 1 of the study: a medical indication, according to routine care, for hospitalization of at least 48 hours for the clinical management of fluoropyrimidine-related toxicity. Exclusion Criteria: Pregnant or breastfeeding women; Known history of allergic reaction to the molecules of the copound and/or to other molecules in the same class; Life expectancy of less than 30 days prior to hospital admission, based on underlying cancer and existing comorbidities; Estimated creatinine clearance \<70 mL/min; Liver cirrhosis; Known liver or kidney disease; Individuals with acquired immunodeficiency may be included only if they have no active opportunistic infections and following careful clinical assessment by the investigator, taking into account concurrent medications; Family history or known deficiency of the enzyme responsible for metabolizing the molecules of the copound and/or to other molecules in the same class; Uncontrolled infection; Hemodynamically unstable patients; Patients under orotracheal intubation; Patients unable to take oral medication; Prolonged QT interval; CNS metastases considered uncontrolled by the investigator; History of malabsorptive or inflammatory gastrointestinal disease; Use within the last 30 days of lactulose, protease inhibitors, amiodarone, carbamazepine, phenytoin, phenobarbital, oxcarbazepine, rifabutin, rifampin, or rifapentine; Use within the last 5 days of dietary supplements containing the molecules of the copound; Use within the last 30 days of drugs classified as anticonvulsants; Personal history of seizures; Comorbidities deemed limiting by the investigator; History of renal or liver transplant; Presence of intestinal obstruction.