Absorption reduced by antacids (Mg, Al or Ca-containing). May increase risk of prolonged QT interval w/ antiarrhythmic agents class IA (eg, quinidine, procainamide) or class III (eg, amiodarone, sotalol). May increase risk of severe tendon disorders (eg, tendinitis; tendon rupture) w/ corticosteroids. May increase risk of CNS stimulation w/ NSAIDs. May increase serum conc & AUC of tizanidine. May increase prothrombin time w/ coumarin. May increase & prolong serum conc & increase risk of adverse effects of theophylline.