Antacids

Inorganic salts that partially neutralize gastric hydrochloric acid.b

Administration

Oral Administration

Administer orally.b

Oral suspensions more rapidly and effectively solubilized than powders or tablets; reserve oral tablets for chronic use in patients who refuse oral suspensions because of inconvenience or unpalatable taste.b Rapidly disintegrating tablets may be a suitable alternative in some patients.b

Chew tablets, including rapidly dissolving tablets, thoroughly before swallowing.b

Dosage

Available as various inorganic salts (e.g., aluminum carbonate, aluminum hydroxide, calcium carbonate, magnesium hydroxide, magnesium oxide, sodium bicarbonate); dosage is expressed in terms of mEq of acid neutralizing capacity.b

Dose and frequency of administration depend on the acid secretory rate of the stomach, gastric emptying time, and the disorder being treated.b

Adults

For peptic ulcer disease, dosages of antacids are empirical and various antacid dosages have been used.b

For supplemental ulcer pain relief, 40–80 mEq acid neutralizing capacity on an as-needed (prn) basis.f

Other therapies currently are preferred for treatment of active peptic ulcers.200 220 234 238 242 243 252 b d (See Peptic Ulcers under Uses.)

If antacids are used for the treatment of peptic ulcers, usual high-dose regimens for ulcer healing employ 80–160 mEq acid neutralizing capacity, given 1 and 3 hours after meals and at bedtime.f

Additional doses of antacids may be administered to relieve ulcer pain that occurs between regularly scheduled doses.b

In patients with duodenal ulcers, antacids usually are given for 4–6 weeks.b If symptoms of duodenal ulcer recur, antacids can be administered 1 and 3 hours after meals and at bedtime for 1 week and, if pain is relieved, less frequently for an additional 1–2 weeks.b

In patients with gastric ulcers, antacids are administered until healing is complete.b

For GERD, dosages of antacids are empirical and various antacid dosages have been used.b d f

For relief of heartburn, one recommended regimen employs 40–80 mEq acid neutralizing capacity on an as-needed (prn) basis intially.d f If necessary, dosage can be titrated to a regularly scheduled basis such as 40–80 mEq acid neutralizing capacity given after meals and at bedtime.d f

In conjunction with dietary phosphate restriction in the management of hyperphosphatemia, 30–40 mL of aluminum hydroxide or aluminum carbonate suspension is administered 3 or 4 times daily.

For calcium replacement dosage with calcium carbonate, see Dosage in Calcium Salts 40:12.

In the management of stress ulceration† and GI bleeding†, antacids are usually administered every hour, and the antacid dosage should be titrated to maintain the nasogastric aspirate above pH 3.5.b

For severe symptoms, antacid suspensions may be diluted with water or milk and given by continuous intragastric infusion.b

To reduce the risk of anesthesia-induced gastric acid aspiration, an antacid suspension has been given 30 minutes before anesthesia.

Prescribing Limits

Adults

Do not exceed 500–600 mEq acid neutralizing capacity daily or regularly scheduled (versus as-needed; prn) therapy for longer than 2 weeks continuously.d f

Maximum daily dosage of sodium or bicarbonate is 200 mEq in patients <60 years of age and 100 mEq in patients >60 years of age.b Contraindicated for prolonged therapy because it may cause metabolic alkalosis or sodium overload.b

Contraindications

• Sodium bicarbonate is contraindicated and use of other sodium-containing antacids should be restricted in patients on low-sodium diets and in those with CHF, renal failure, edema, or cirrhosis.b

Warnings/Precautions

Warnings

Some antacids may contain aspartame (e.g., NutraSweet), which is metabolized in the GI tract to phenylalanine following oral administration.b

Sensitivity Reactions

Some antacid formulations contain the dye tartrazine (FD&C yellow No. 5), which may cause allergic-type reactions (bronchial asthma in susceptible individuals) in certain susceptible individuals (e.g., patients who are sensitive to aspirin).b

General Precautions

Risk of hypophosphatemia with prolonged administration or large doses, particularly in patients with inadequate dietary intake of phosphorus.b

Monitor serum phosphate concentrations at monthly or bimonthly intervals in patients on maintenance hemodialysis who are receiving chronic aluminum antacid therapy.b

May cause gastric hypersecretion and acid rebound.b

May cause the milk-alkali syndrome (characterized by hypercalcemia, metabolic alkalosis and, rarely, renal insufficiency).b

Monitor serum calcium concentrations weekly and whenever manifestations of hypercalcemia occur in patients receiving large doses of calcium carbonate.b

Commonly cause a laxative effect, and frequent administration of these antacids alone often cannot be tolerated; repeated doses cause diarrhea which may cause fluid and electrolyte imbalances.b

May cause metabolic alkalosis when given in large doses.b

Serious medication errors have been reported to FDA in which consumers used Maalox Total Relief (bismuth subsalicylate) when they intended to use traditional Maalox liquid antacid products containing aluminum hydroxide, magnesium hydroxide, and simethicone (e.g., Maalox Advanced Regular Strength, Maalox Advanced Maximum Strength).266 267 268 Because of the potential for serious adverse effects associated with accidental use of bismuth subsalicylate (which is chemically related to aspirin), the manufacturer of Maalox Total Relief initially agreed to change the trade name of the product to one that did not include “Maalox”; however, the manufacturer instead discontinued the bismuth subsalicylate preparation in the summer of 2010.267 269

Specific Populations

Aluminum Antacids: Long-term administration in patients with renal failure or chronic renal failure may result in hyperaluminemia since small amounts of aluminum are absorbed from the GI tract and excretion of aluminum is decreased in patients with renal failure.b Aluminum accumulation in the CNS may be the cause of dialysis encephalopathy, while aluminum accumulation in the bones may result in or worsen dialysis osteomalacia.b

Calcium Carbonate: Patients with renal impairment or dehydration and electrolyte imbalance are predisposed to developing the milk-alkali syndrome.b Hypercalcemia risk in chronic hemodialysis patients.b

Magnesium Antacids: In patients with severe renal impairment, hypermagnesemia characterized by hypotension, nausea, vomiting, ECG changes, respiratory or mental depression, and coma.b Do not administer in patients with renal failure, and antacids containing more than 50 mEq of magnesium in the recommended daily dosage should be used cautiously and only under the supervision of a clinician who should monitor electrolytes in patients with renal disease.b

Sodium Bicarbonate: May cause metabolic alkalosis in patients with renal insufficiency.b

Common Adverse Effects

With prolonged administration, constipation (e.g., aluminum salts, calcium carbonate), diarrhea (e.g., magnesium salts), gastric distension/flatulence (e.g., sodium bicarbonate), and gastric hypersecretion/acid rebound (e.g., calcium carbonate).b

• Mechanism of action in the treatment of peptic ulcers is based on ability of antacids to react with hydrochloric acid and thus increase gastric pH.b

• With usual doses, antacids generally do not increase and maintain gastric pH above 4–5.b

• Antacids, in decreasing order of their ability to neutralize a given amount of acid, are calcium carbonate, sodium bicarbonate, magnesium salts, and aluminum salts.b

• Aluminum-containing antacids (except aluminum phosphate) combine with dietary phosphate in the intestine forming insoluble, nonabsorbable aluminum phosphate which is excreted in the feces.b If phosphate intake is limited and renal function is normal, aluminum antacids (except aluminum phosphate) decrease phosphate absorption and hypophosphatemia and hypophosphaturia occur.b

• Magnesium-containing antacids have a laxative action.b

• Advise patients to consult a clinician if ulcer pain worsens or is not relieved after the first week of therapy.b

• Importance of consulting a clinician if GERD symptoms persist or warning signs of more severe GERD develop (e.g., dysphagia, bleeding, weight loss, choking [acid-induced cough, shortness of breath, and/or hoarseness], chest pain).265 d

• Importance of women informing their clinician if they are or plan to become pregnant or plan to breast-feed.b

• Importance of informing clinicians of existing or contemplated concomitant therapy, including prescription and OTC drugs, as well as concomitant illnesses.b

• Importance of informing patients of other important precautionary information.b (See Cautions.)