 Antacids: weak bases that react with hydrochloric acid to form salt & water. 

o Used in the treatment of Hyperacidity, GERD, PUD, hyperphosphatemia, and calcium deficiency

o Contain combinations of 

 metallic cation (aluminum, calcium, magnesium, and sodium) 

 and basic anion (hydroxide, bicarbonate, carbonate, citrate, and trisilicate)

 Pharmacodynamics, Pharmacokinetics, Pharmacotherapeutics

o Neutralize Gastric Acidity (causes ^pH of the stomach and duodenal bulb)

o Inhibit proteolytic activity of pepsin

o Increase lower esophageal sphincter tone

o Acid-neutralizing capacity ANC varies between products expressed in mEqs

o If ingested in a fasting state, antacids reduce acidity for approximately 20 to 40 minutes

o If taken 1 hr after a meal, acidity is reduced for 2 to 3 hrs

o A second dose taken after a meal maintains reduced acidity for more than 4 hrs after the meal

o The action of antacids occurs locally in the GI tract with minimal absorption, minimal metabolism

o ALL antacids are contraindicated in the presence of severe abdominal pain of unknown cause, especially if accompanied by fever

-HIGH SODIUM content: pts w/ HTN, CHF, marked renal failure, or on low-sodium diets need to use low sodium preparation

-Concurrent administration with enteric-coated drugs, destroys the coating= alters absorption, ^ the risk for adverse effects

-Administrations should be separated by at least 2 hours to decrease drug/drug interactions

1. Calcium based antacids: TUMS, Caltrate, Calcarb

• Prescribed to treat calcium deficient states, i.e. chronic renal failure, post-menopause, and osteoporosis 

• Used to bind phosphates in CRF

• Require Vitamin D for absorption from the GI tract

• Excreted mainly in feces, 20% in urine

• ADR: Contraindicated in the presence of hypercalcemia and renal calculi

• Can cause constipation- increase bulk, fluids and mobility, stool softener

• Administered 30min- 1hr on empty stomach or 3hr after meals

• Should not be administered with food containing large amounts of oxalic acid (spinach, rhubarb), or phytic acid (bran, cereals), they decrease the absorption of calcium

• Taking w/ foods containing phosphorus (milk, dairy) can lead to milk-alkali syndrome (N/V, confusion, headache). 

• Taking with acidic fruit juice improve absorption

2. Aluminum based: AlternaGEL, Amphojel, Mylanta

• Inhibit smooth muscle contraction and slow gastric emptying

• Used to bind phosphates in CRF

• Not absorbable with routine use

• Aluminum concentrated in the CNS

• Bind with phosphate and excreted in feces

• Prolonged use in patients with renal failure may result in dialysis osteomalacia

o Aluminum deposits in bone and osteomalacia occurs

• Elevated aluminum tissue levels contribute to the development of dialysis encephalopathy 

• Used to treat hyperphosphatemia in pts w/ renal failure & phosphate renal stone prevention

• Can cause constipation- increase bulk, fluids and mobility, stool softener

3. Magnesium based: Milk of mag, Maalox, Mylanta

• Can be used to treat magnesium deficiencies from malnutrition, alcoholism, or mag-depleting drugs

• Contraindicated in patients with renal failure & used with caution in pts with renal insufficiency

• Not absorbable with routine use

• Excreted in the urine

• Contraindicated in patients with renal failure, use with caution for patients with any degree of renal insufficiency

o Malfunctioning kidney is unable to excrete magnesium and hypermagnesemia may result

• Can cause diarrhea- increase fiber intake  (Alkalosis may occur in renal impairment)

Clinical Use and Dosing