Formal interaction studies have not been performed with Colazide. Available data suggest that the systemically available amounts of balsalazide and its metabolites may be increased if Colazide is administered in the fasting as compared with the fed state. Therefore, Colazide should preferably be administered with food.
The acetylated metabolites of balsalazide are actively secreted in the renal tubule to a high degree. Therefore, plasma levels of co-prescribed drugs also eliminated by this route may be raised and this should be noted in the case of those with a narrow therapeutic range, such as methotrexate.
Pharmacodynamic interactions have not been studied. However, while balsalazide, mesalazine, and N-acetylmesalazine are salicylates chemically, their properties and kinetics make classical salicylate interactions such as those found with acetylsalicylic acid very unlikely.
The uptake of digoxin has been impaired in some individuals by concomitant treatment with sulphasalazine. Even if it is not known whether this would occur also during treatment with balsalazide, it is recommended that plasma levels of digoxin should be monitored in digitalised patients starting Colazide.
Mesalazine inhibits thiopurine methyltransferase. In patients receiving azathioprine or 6-mercaptopurine, caution is recommended for concurrent use of mesalazine as this can increase the potential for blood dyscrasias.