Graph with pH curves of different antacids

If every dot represents the addition of 0.1 g of the respective base. I suppose that the best would be the one that reaches the highest pH, in the shortest time, for example Calcium Carbonate, but if that is true, why are other antacids used that reach lower pH?

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    $\begingroup$ You shouldn't just consider the efficiency of antacid. Most efficient antacids can also be very dangerous to human health! $\endgroup$ – Mockingbird Feb 24 '17 at 20:09
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    $\begingroup$ I read that there are two dangers with using antacids. First is alkalosis, when the pH goes higher than 7, and acid rebound when the stomach will produce even more acid to neutralize the extra base. So if that is not it what would be measured as efficiency? $\endgroup$ – Theodore Visvikis Feb 24 '17 at 20:18
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    $\begingroup$ Your experiment is an interesting approach to this question. Your result basically show that carbonate based antacids behave one way and the aluminum hydroxide / magnesium hydroxide ones another. The latter two (the hydroxides) are so insoluble in water (though obviously soluble in acid) that they seem to take much longer to dissolve than the calcium carbonate and Rennie (calcium carbonate). I think that you will find that the carbonates act the fastest, though maybe won't last the longest. This just a measure of relative speed of dissolution though, not efficiency or quality. $\endgroup$ – airhuff Feb 24 '17 at 23:45
  • $\begingroup$ @airhuff So what do you suggest for judging efficiency? $\endgroup$ – Mockingbird Feb 25 '17 at 7:46
  • $\begingroup$ Speed isn't everything. Some manufacturers will sacrifice speed (which they all know how to get) in the interest of more controlled pH, cutting down the risk of alkalosis or acid rebound described in other comments (@Theodore). $\endgroup$ – Oscar Lanzi Nov 27 '17 at 19:06

Normally, the efficacy of a drug is determined by the area under the curve of the entire time course of the drug in the body. The graphs here only show the initial rate of the change in pH but not the entire time course after the peak pH is reached. I assumed that these results were generated by an acid-base titration experiment in the laboratory and not generated in vivo. Therefore I cannot answer which antacid is more effective and/or clinically safe.

Although calcium carbonate shows a rapid initial rate of pH neutralization, it may not be suitable for all patients. Too rapid a pH rise in the digestive tract may cause nausea and vomiting and may trigger an “acid rebound”, meaning that the body tries to compensate by secreting more acid to maintain the normal gastric pH for food digestion, making the heartburn even more unbearable.

Some patients take calcium carbonate as a source of calcium, but one also needs vitamin D in order for the calcium to be absorbed. Besides, calcium carbonate yields carbon dioxide gas with acid which is still acidic, and bloating. For patients with compromised parathyroid function, too much calcium in the blood (hypercalcemia) after the bones are already saturated with calcium may start to deposit in the heart and in the kidneys to form calcium oxalate kidney stones (different from uric acid stone). Therefore calcium antacid may not be the best antacid for all patients.

If calcium antacid is not tolerable, one can use aluminum hydroxide (Aludrox®) which is a good alternative. However aluminum hydroxide can cause constipation. Magnesium hydroxide (milk of magnesia) is another good alternative, but magnesium hydroxide can cause diarrhea because magnesium is a smooth muscle relaxant. Therefore the product Maalox® or Mylanta® which combines aluminum hydroxide with magnesium hydroxide will be easier on the stomach. Also, there are products that contain simethicone (which is an anti-flatulent) as an extra ingredient to help with bloating.

The choices for an antacid are out there, make a good, sound one.

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    $\begingroup$ Acid-base chemistry has different pharmacokinetics from regular small molecules. The drug will react in-situ on the order of minutes in the stomach, and opposed to being processed by the liver or just secreted via kidneys. What you see via the graphs is what you get in terms of efficacy, though clearly not in terms of side-effects as your answer so nicely points out. $\endgroup$ – Zhe Mar 7 '19 at 18:14
  • $\begingroup$ Thank you for the comment. I was answering the part of the question that asked why other antacids are used. $\endgroup$ – Isaac Lai Mar 7 '19 at 19:17
  • $\begingroup$ Don't get me wrong. This is not a complaint about your answer. I am simply extending discussion about the first line of your answer. $\endgroup$ – Zhe Mar 7 '19 at 20:36
  • $\begingroup$ You are welcome. $\endgroup$ – Isaac Lai Mar 7 '19 at 23:48

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