Erdafitinib is a kinase inhibitor indicated for the treatment of adult patients with locally advanced or metastatic urothelial carcinoma (mUC) who have:

• Susceptible FGFR3 or FGFR2 genetic alterations, and
• Experienced disease progression during or after at least one prior platinum-containing chemotherapy regimen, including progression within 12 months of neoadjuvant or adjuvant platinum-based therapy.

Erdafitinib is a tyrosine kinase inhibitor that targets and inhibits FGFR1, FGFR2, FGFR3, and FGFR4 enzymes. It also interacts with other kinases such as RET, CSF1R, PDGFRA, PDGFRB, FLT4, KIT, and VEGFR2. By blocking FGFR phosphorylation and downstream signaling pathways, erdafitinib reduces cell viability in tumor cells with FGFR alterations, including mutations, amplifications, and gene fusions. It has demonstrated antitumor activity in both cell-based and animal (xenograft) models, particularly in cancers expressing FGFR alterations such as bladder cancer.

The recommended starting dose of Erdafitinib is 8 mg (two 4 mg tablets) orally once daily, with a dose increase to 9 mg (three 3 mg tablets) once daily based on serum phosphate (PO₄) levels and tolerability at 14 to 21 days. Treatment should be continued until disease progression or unacceptable toxicity occurs.

If a dose of Erdafitinib is missed, it can be taken as soon as possible on the same day. The regular daily dose schedule for Erdafitinib should be resumed the next day. Extra tablets should not be taken to make up for the missed dose.

Moderate CYP2C9 or Strong CYP3A4 Inhibitors: When Erdafitinib is used together with moderate CYP2C9 inhibitors or strong CYP3A4 inhibitors, alternative medications should be considered. If the combination is unavoidable, patients should be closely monitored for possible adverse reactions.

Strong CYP2C9 or CYP3A4 Inducers: Concurrent use of Erdafitinib with strong CYP2C9 or CYP3A4 inducers should be avoided because these drugs may reduce the effectiveness of erdafitinib.

Moderate CYP2C9 or CYP3A4 Inducers: If Erdafitinib is used with moderate CYP2C9 or CYP3A4 inducers, the dose of Erdafitinib may need to be increased up to 9 mg.

Agents Affecting Serum Phosphate Levels: Medications that significantly alter serum phosphate levels should be avoided before the initial dose adjustment period of Erdafitinib treatment.

CYP3A4 Substrates: Caution should be taken when Erdafitinib is used with sensitive CYP3A4 substrates with a narrow therapeutic index, as this combination may increase the risk of toxicity.

OCT2 Substrates: When used with OCT2 substrate drugs, alternative medicines or dose reduction of the OCT2 substrate should be considered depending on patient tolerance.

P-gp Substrates: When using Erdafitinib with P-gp substrates with a narrow therapeutic index, dosing should be separated by at least 6 hours before or after administration.

The most commonly reported adverse reactions, including laboratory abnormalities (≥20%), include increased phosphate levels, stomatitis, fatigue, elevated creatinine, diarrhea, dry mouth, nail disorders, increased alanine aminotransferase, elevated alkaline phosphatase, decreased sodium, reduced appetite, decreased albumin, dysgeusia, decreased hemoglobin, dry skin, elevated aspartate aminotransferase, decreased magnesium, dry eyes, alopecia, palmar-plantar erythrodysesthesia syndrome, constipation, decreased phosphate, abdominal pain, increased calcium, nausea, and musculoskeletal pain.

Eye Disorders: Erdafitinib may cause central serous retinopathy or retinal pigment epithelial detachment (CSR/RPED). Eye examinations should be performed monthly during the first four months, then every three months, or whenever visual symptoms appear. If CSR/RPED occurs, treatment should be paused and permanently discontinued if symptoms do not resolve within four weeks or become severe.

Hyperphosphatemia: Blood phosphate levels should be regularly monitored, and dose adjustments should be made if necessary.

Embryo-Fetal Toxicity: Erdafitinib may cause harm to an unborn baby. Patients should be advised to use effective contraception during treatment.

Pediatric Use: The safety and effectiveness of Erdafitinib in children have not been established.

Geriatric Use: Clinical studies did not show significant differences in safety or effectiveness between elderly and younger patients.

Renal Impairment: No dose adjustment is required for mild to moderate kidney impairment.

Hepatic Impairment: No dose adjustment is required for mild or moderate liver impairment, but limited data are available for severe liver impairment.

CYP2C9 Poor Metabolizers: Patients with the **CYP2C93/3 genotype may have higher plasma levels of Erdafitinib and should be monitored carefully for increased side effects.

Cytotoxic Chemotherapy

Store Erdafitinib below 30°C in a cool and dry place. Protect from light and keep out of the reach of children.