Snapshot A 30-year-old lawyer presents to her primary care physician for the evaluation of nonbloody diarrhea. She reports that she has around 2 episodes a day and that her stool consistency is very watery. As her physician asks about any travel or food exposures, she takes out a pill and pops one in her mouth. When asked about this, she reports, “I have been under so much stress lately and these antacids are helping with my abdominal pain.” On closer exam, these pills are magnesium hydroxide. She is counseled about the side effects of osmotic diarrhea. Introduction Drugs aluminum hydroxide calcium carbonate magnesium hydroxide Mechanism of action neutralizes acid in the stomach delays gastric emptying Antacids Aluminum Hydroxide Calcium Carbonate Magnesium Hydroxide Mechanism of action Neutralizes acid in the stomach Delays gastric emptying Neutralizes acid in the stomach Delays gastric emptying Neutralizes acid in the stomach Delays gastric emptying Also acts as a phosphate binder Also acts as a phosphate binder Promotes osmotic retention of fluid and induces diarrhea Clinical use Acid reflux Peptic ulcer disease Aluminum hydroxide Acid reflux Peptic ulcer disease Aluminum hydroxide Acid reflux Peptic ulcer disease Aluminum hydroxide Hyperphosphatemia Calcium supplementation Constipation Adverse effects Constipation Decreased phosphatemuscle weaknessosteodystrophy Milk-alkali syndrome ↑ calcium in severe cases, can cause metastatic calcification and renal failure Can chelate and decrease the efficacy of some drugs, particularly tetracyclines (doxycycline, tetracycline, and minocycline) Diarrhea Hypotension Cardiac arrest