Interaction of magnesium oxide with gastric acid secretion inhibitors in clinical pharmacotherapy

Purpose

Magnesium oxide (MgO), a short-term osmotic laxative, is converted into MgCl₂ under acidic condition in the stomach and then Mg(HCO₃)₂ in the intestinal tract, where Mg(HCO₃)₂ induces the water exudation into the intestine. This indicates that the laxative effect of MgO could be attenuated under the suppressed gastric acid secretion. In this study, the possible interaction of MgO with gastric acid secretion inhibitors was evaluated by using electronic patient records of MgO dosage levels.

Methods

Defecation was controlled with MgO alone in some patients after colon surgery (n?=?67) and after total gastric resection (n?=?4). Some other patients were treated with a combination use of MgO and H₂ receptor antagonist (H₂RA) (n?=?14) or proton pump inhibitor (PPI) (n?=?27). The possible drug interaction of MgO with H₂RA or PPI was evaluated by comparing dosage levels of MgO used in controlling defecation.

Results

In controlling defecation, the daily dosage levels of MgO in patients taking H₂RA or PPI and patients with total gastric resection were significantly higher than those patients taking MgO alone after colon surgery. The ratios of good constipation control (controlled well at the dosing level of 1,000 mg MgO) in patients taking H₂RA or PPI were significantly lower than that in patients treated with MgO alone. In an in vitro study, the solubility of MgO at pH 4.5 was quite low, as compared with that at pH 1.2.

Conclusions

When patients received H₂RA or PPI, the laxative effect of MgO is decreased possibly due to the low solubility of MgO at the higher gastric pH and less generation of MgCl₂ and Mg(HCO₃)₂. Higher dosing level of MgO or another laxative should be used in patients taking H₂RA or PPI, as well as the case of patients with total gastric resection.