Mechanism of action:
Antacids are alkaline substance that have been used o neutralize stomach acid for hundreds of years. They are inorganic compounds of aluminum, magnesium, sodium or calcium. Combination of aluminum hydroxide and magnesium hydroxide, the most common type, are capable of rapidly neutralizing of stomach.
Antacids act within 10 to 15 minutes, but their duration of action is only 2 hrs. Because of that, they are taken during the day. Absorption of antacids is clinically unimportant unless the patient is on a sodium-restricted diet or has diminished renal function that could result in the accumulation of the minerals.

Relieve symptoms of hyperacidity, GERD, & pain d/t duodenal ulcers

Calcium Carbonate
Sodium Bicarbonate

Aluminum hydroxide
Calcium carbonate
Calcium carbonate with magnesium hydroxide
Magnesium hydroxide (Milk of magnesia)
Magnesium hydroxide with aluminum hydroxide sometime with Simethicone
Sodium bicarbonate

Adverse effects:
Al antacids (Amphojel) – constipation
Mg antacids (MOM) – diarrhea & renal problems
Ca antacids (Tums) – constipation & gas & may aggravate kidney stone
Administration of calcium antacids with milk or any item with Vitamin D can cause milk-alkali syndrome to occur. Early symptoms of hypercalcemia and include headache, urinary frequency, anorexia, nausea, and fatigue. It can cause permanent renal damage.
Na Bicarb antacids – raise B/P & worsen CHF

Pharmaceutical companies combine aluminum and magnesium together to counteract their adverse effects, which are constipation and diarrhea.
Simethicone is sometimes added to antacids preparations, because it reduces gas bubbles that cause bloating and discomfort. It is also used as the flatus relief alone.
Magnesium based antacids are not choice for the renal disorder, but physician might prescribed because of magnesium deficiency (so check lab values before changing antacids).

Nursing consideration:
Many interactions

Give 2 hrs after other drugs

Give 1 -3 hrs pc and hs

Avoid Mg based agents w/ renal failure

Al carbonate (Amphojel) antacid of choice for renal failure