Taking Spironolactone and Lasix in one day, especially when your body's systems are over burdened by other substances in your system is very dangerous. Lasix decreases and Spironolatone increases serum potassium. Effects of their interaction is not clear. Potential for dangerous ineraction Use with caution and monitor closely. The Spironolactone & Lasix do not counteract each drugs effect on the users potassium. Potassium is a major intracellular cation and critical to cardiac and muscle function.