Sulfasalazine can get in the way of Digoxin being absorbed from your gut into your blood. If you take the two together, the amount of Digoxin in your blood may end up lower than it should be. That means Digoxin may not work as well as it is meant to.
These medicines are often taken together with some care. Your doctor may change a dose, space them apart or check on you more often. Make sure your doctor and pharmacist know you take both.