Folic acid Magnesium trisilicate

Iwuagwu MA, Jideonwo A. Preliminary investigations into the in-vitro interaction of folic acid with magnesium trisilicate and edible clay. Int J Pharm 1990 65 63-67. 

Magnesium trisilicate, when taken with drugs such as mebeverine hydrochloride, proguanil, norfloxacin, sucralfate, and tetracycline, may cause a reduction in bioavailability via binding or chelation. The dissolution rate of folic acid, erythromycin stearate, paracetamol, and chloroquine phosphate may be retarded by adsorption onto magnesium trisilicate. Antimicrobial preservatives, such as the parabens, may be inactivated by the addition of magnesium trisilicate. Magnesium trisilicate is also readily decomposed by mineral acids. 

In vitro studies show that folic acid is markedly adsorbed by magnesium trisilicate and edible clay9 This would be expected to reduce its absorption from the gut, but the clinical importance of this awaits assessment. 

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