Calcium resonium powder contains the active ingredient calcium polystyrene sulphonate, which is a type of medicine called an ion exchange resin. Calcium polystyrene sulphonate binds with potassium in the gut, forming a complex that cannot be absorbed into the blood. This effectively reduces the levels of potassium in the bloodstream. It is used in situations where the level of potassium in the blood is too high, for example, in people who are not producing urine, or in people with severe kidney failure who are having dialysis. Calcium resonium powder can be given either by mouth, or rectally as an enema. Follow the instructions given by your doctor.