Rituxan interactions. Drug interactions may change how your medications work or increase your risk for serious side effects. This document does not contain all possible drug interactions. Keep a list of all the products you use (including prescription/nonprescription drugs and herbal products) and share it with your doctor and pharmacist. Do not start, stop, or change the dosage of any medicines without your doctor’s approval. Some products that may interact with this drug are: other drugs that weaken the immune system/increase the risk of infection (such as tofacitinib, natalizumab, fingolimod).