Doxazosin is bound to plasma proteins. In in vitro tests, doxazosin had no influence on the binding of digoxin, warfarin, phenytoin or indomethacin to plasma proteins. No harmful interactions were observed in patients taking doxazosin together with thiazide diuretics, furosemide, beta-antagonists, nonsteroidal anti-inflammatory drugs, antibiotics, oral hypoglycemic drugs, uricosuric drugs and anticoagulants.