This document discusses several important drug interactions with hydroxychloroquine. It notes that hydroxychloroquine can increase serum digoxin levels when taken with heart drugs like digoxin, increasing the risk of side effects. It also warns that hydroxychloroquine may increase the hypoglycemic effects of insulin and antidiabetic drugs, requiring a possible dosage reduction. Additionally, hydroxychloroquine can increase the risk of ventricular arrhythmias when combined with antiarrhythmic drugs and may decrease seizure thresholds when taken with other antimalarial or antiseizure medications.