Antacids and sucralfate

Pharmacology

Antacids are basic compounds which neutralize hydrochloric acid in the gastric secretions. For this purpose, the following arc used:

■ sodium hydrogen carbonate, aluminum hydroxide, aluminum phosphate, algeldrate, calcium carbonate, magnesium(hydr)oxide, magnesium carbonate, and magnesium trisilicate u combination preparations of aluminum, magnesium, and carbonate m the structurally newer aluminum-magnesium complexes almasi-late, hydrotalcite, and magaldrate; and the aluminum saccharide combination, sucralfate.

Regarding aluminum-containing antacids, the bioavailability of ingested aluminum is reported to be 0.01-1% (Greger 1993). Priest reports, referring to studies employing 26Al as a tracer, that approximately 0.01% of ingested aluminum, as aluminum hydroxide, may be absorbed. Co-administration of citrate may enhance the uptake a tenth-fold, up to 0.14%. Excretion occurs primarily through the kidneys; about 2% of aluminum entering the blood is retained within the body for years (Priest 2004). Renal failure may reduce renal excretion of aluminum. Because of its molecular structure, the aluminum bound in the newer complex preparations like magaldrate may be more poorly absorbed in comparison to aluminum in classical antacids. It has been shown in animal studies that the absorbed aluminum salts can also rcach the fetus (Domingo 2000). Aluminum-containing antacids can be constipating.

Regarding calcium-containing antacids, about 15-30% of oral calcium carbonate intake is absorbed. In patients with normal kidney function, there is no danger of hypercalcemia with normal ther apeutic use. High intake of calcium carbonate antacids has been associated with (life-threatening) milk-alkali syndrome during pregnancy (Gordon 2005).

Regarding magnesium-containing antacids, about 5-10% of ora! magnesium intake may be absorbed. Magnesium-containing antacids bave a laxative effect.

Chronic consumption of high doses of antacids can cause alterations in mineral metabolism.

Sucralfate, a water-soluble aluminum salt of a sulfated polysaccharide, attaches to the surface of an ulcer and thus protects the mucosa from further injury by acid and pepsin. The systemic absorption of sucralfate is negligible.

Toxicology

Antacids are generally considered safe in pregnancy. The available data do not suggest teratogenic effects or other developmental toxicity associated with normal therapeutic use of antacids during pregnancy.

It has been proposed that the aluminum absorbed from aluminum-containing antacids could lead to functional disturbances in potentially sensitive organs in the fetus, such as the central nervous system and the kidneys. A 1998 case report has described a 9-year-old with a fatal neurodegenerative disorder, whose mother had taken an excessive amount of aluminum hydroxide {an average of 15 000 mg daily) throughout the entire pregnancy. The authors postulate that the high levels of aluminum ingested by this mother during pregnancy resulted in neurologic impairment in this infant (Gilbert-Barness 1998). However, with normal therapeutic use there have been no clinical indications of teratogenic effects or other developmental toxicity.

In a case reported by Robertson (2002), it is suggested that maternal ingestion of high doses of calcium carbonate-containing antacid may have temporarily suppressed neonatal parathormone production, causing neonatal seizures secondary to late neonatal hypocalcemia. However, there have been no clinical indications of teratogenic effects or other developmental toxicity with normal therapeutic use.

Antacids containing sodium bicarbonate can induce maternal and fetal metabolic alkalosis and fluid overload (review by Richter 2003, Cappell 1998, Katz 1998).

Compounds containing magnesium trisilicate, when used long term and in high doses, can lead to nephrolithiasis, hypotonia, respiratory distress and cardiovascular impairment in the fetus (review by Richter 2003, Cappell 1998, Katz 1998).

Generally speaking, magnesium salts can inhibit contractions (see Chapters 2.8 and 2.14), but after oral ingestion as an antacid, with its limited systemic absorption, such an effect is unlikely to occur.

Antacids may interfere with iron absorption (review by Richter 2003, Cappell 1998, Katz 1998).

Recommendation. Antacids and sucralfate may be used during all phases of pregnancy. The unrestricted/long-term use of antacids during pregnancy should be avoided. Among the aluminum-containing antacids, magaldrate and sucralfate may be considered the drugs of choice because of their apparently limited aluminum absorption.

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