Common use of PEG or magnesium hydroxide-containing preparations(milk of magnesia) in patients with congestive heart failure or chronic renal disease should be done with extreme caution as they can cause electrolyte imbalances, such as hypokalemia and diarrhea, further worsening fluid-electrolyte balances. Osmotic agents are useful when first-line bulking agents and/or stool softners are not effective.