Explore the effects of prolonged use of antacids on acid base balance?

Answer:
Calcium antacids seems to have an alkalyzing effect.This excerpt comes from:
ACID-BASE IN RENAL FAILURE
New Perspectives on Acid-Base Balance /Man S. Oh
Seminars in Dialysis
Volume 13 Issue 4 Page 212 - July-August 2000
[If you or your library subscribes to this journal, it can
be accessed through the Internet at: http://www.blackwell-synergy.com/doi/ful... ]"The overall alkalinizing effect of various calcium antacids depends less on the absorption of calcium than on the ability of calcium to bind phosphate, because the amount of calcium absorbed is usually much less than the amount excreted in combination with phosphate. The phosphate-binding ability depends in part on the availability of soluble calcium. The amount of phosphate bound by calcium when calcium is ingested as CaCl2 is comparable to that bound by aluminum ingested as Al(OH)3. For each 100 mEq of either antacid ingested, phosphate excreted was 11.9 mEq with CaCl2 and 11.4 mEq with Al(OH)3(28). However, when calcium was ingested as a carbonate salt, only half as much phosphate (6 mEq) was removed for the same amount of calcium. The likely explanation is the poor solubility of CaCO3. On the other hand, even if conversion of CaCO3 to CaCl2 in the stomach were complete, the phosphate binding ability might be different in this situation, since complete conversion requires a large amount of HCl secretion and the resulting low pH tends to enhance phosphate absorption in the duodenum. Calcium acetate binds phosphate better than CaCO3, most likely because the former is more soluble than the latter. Calcium acetate is a much more effective binder of phosphate than calcium citrate, probably because it is more soluble than calcium citrate, and also because citrate tends to bind calcium more avidly than acetate (29).
[29. Sheikh MS, Maguire JA, Emmett M, et al: Reduction of dietary phosphorus absorption by phosphorus binders. J Clin Invest 83:66 73, 1989 ]However, there seems to be no change in the acid base balance
with magnesium or aluminum.This excerpt came from the UpToDate topic
Electrolyte complications of antacid therapy
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METABOLIC ALKALOSIS 鈥?Antacids typically contain magnesium or aluminum in combination with an alkali anion such as hydroxide. The hydroxide component buffers gastric hydrogen ions while the magnesium combines with pancreatic bicarbonate to form insoluble magnesium carbonate. The net effect of these reactions is equivalent hydrogen and bicarbonate loss and no change in acid-base balance. Some of the magnesium, however, normally combines with other constituents in the intestinal lumen, such as fats and phosphates. As a result, some of the secreted bicarbonate remains soluble and is absorbed, leading to a mild alkaline load that produces no problems as long as renal function is relatively normal [1,2].
1. Stemmer, CL, Oster, JR, Vaamonde, CA, et al. Effect of routine doses of antacid on renal acidification. Lancet 1986; 2:3.
2. Fitzgibbons, LJ, Snoey, ER. Severe metabolic alkalosis due to baking soda ingestion: case reports of two patients with unsuspected antacid overdose. J Emerg Med 1999; 17:57. Hoping this additional info is of some use,
Janice

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Chronic use of calcium carbonates can cause the Milk-Alkali Syndrome. Findings include hypercalcemia, nephrocalcinosis, renal insufficiendy, and metabolic alkalosis.

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