Drug Interaction Report

MONITOR CLOSELY: Coadministration of radium Ra 223 dichloride (Ra-223 dichloride) with other agents that can cause bone marrow suppression or myelosuppression may result in additive toxicity. Ra-223 dichloride alone is associated with thrombocytopenia, neutropenia, pancytopenia, and leukopenia; death from bone marrow failure has also been reported. In a randomized clinical trial in patients with metastatic castration-resistant prostate cancer with bone metastases, 2% of the patients on Ra-223 dichloride experienced bone marrow failure or ongoing pancytopenia compared to no patients in the placebo group. Grade 3-4 adverse reactions of thrombocytopenia and neutropenia were more commonly reported in patients who had received prior docetaxel. However, data from clinical drug interaction studies are lacking.

MANAGEMENT: Caution and close monitoring for additive hematologic toxicity are recommended if concomitant use of Ra-223 dichloride with other agents that can cause bone marrow suppression or myelosuppression is required. The manufacturer advises that Ra-223 dichloride be discontinued in patients requiring administration of chemotherapy, other systemic radioisotopes, or hemibody external radiotherapy. If concomitant use is required, the manufacturer's product labeling should be consulted for specific hematologic monitoring and dose adjustment recommendations. Some authorities recommend not initiating subsequent systemic cancer treatment for at least 30 days after the last administration of Ra-223 dichloride. Patients should be advised to contact their physician if they develop signs or symptoms of myelosuppression or infection including but not limited to pallor, dizziness, fatigue, lethargy, fainting, easy bruising or bleeding, fever, chills, sore throat, body aches, and/or other influenza-like symptoms.

ADJUST DOSING INTERVAL: Oral cladribine may increase the bioavailability of other drugs, which may increase the risk or severity of adverse reactions. Cladribine tablets may contain hydroxypropyl betadex, which could form a complex with the active ingredients of other drugs, especially agents with low solubility. The clinical relevance of this interaction remains unknown.

MANAGEMENT: Administration of oral cladribine should be separated from any other oral drug by at least 3 hours.