Fostamatinib (Tavalisse) can be used to treat immune thrombocytopenia, as it can improve platelet levels and reduce the risk of bleeding. What precautions should patients take when taking fostamatinib?

Effects of other drugs on fostamatinib

(1) Strong CYP3A4 inhibitors

Concomitant use of fostamatinib with strong CYP3A4 inhibitors will increase the exposure of R406 (the main active metabolite), which may raise the risk of adverse reactions. Therefore, when used in combination with strong CYP3A4 inhibitors, it is necessary to monitor the dose-related toxicity of fostamatinib and consider whether dosage adjustment is needed. Strong CYP3A4 inhibitors include itraconazole (a broad-spectrum antifungal drug), ketoconazole (a broad-spectrum antifungal drug), voriconazole (a broad-spectrum antifungal drug), etc.

(2) Strong CYP3A4 inducers

Concomitant use of fostamatinib with strong CYP3A4 inducers can reduce the exposure of R406, so it is not recommended to use fostamatinib in combination with strong CYP3A4 inducers. Strong CYP3A4 inducers include rifampicin (anti-tuberculosis), rifapentine (anti-tuberculosis and anti-leprosy), phenytoin (anti-epileptic, anti-arrhythmic, and for trigeminal neuralgia), etc.

Effects of fostamatinib on other drugs

(1) CYP3A4 substrates

Concomitant use of fostamatinib with CYP3A4 substrates may increase the drug concentration of some CYP3A4 substrates. Therefore, when used in combination with CYP3A4 substrates, it is necessary to monitor the dose-related toxicity of fostamatinib and consider whether dosage adjustment is needed. CYP3A4 substrates include cimetidine, ketoconazole, acetaminophen, etc.

(2) BCRP substrates

Concomitant use of fostamatinib with BCRP substrates may increase the drug concentration of some BCRP substrates. Therefore, when used in combination with BCRP substrates, it is necessary to monitor the dose-related toxicity of fostamatinib and consider whether dosage adjustment is needed. BCRP substrates include methotrexate, daunorubicin, mitoxantrone, etc.

(3) P-gp substrates

Concomitant use of fostamatinib with P-gp substrates may increase the drug concentration of P-gp substrates (such as digoxin). It is necessary to monitor the toxicity of P-gp substrate drugs, and dosage reduction may be required when used in combination with fostamatinib. P-gp substrates include pazopanib (for advanced renal cell carcinoma, soft tissue sarcoma, epithelial ovarian cancer, and non-small cell lung cancer), everolimus (for advanced renal cell carcinoma and pancreatic neuroendocrine tumors), etc.