Magnesium trisilicate Chloroquine

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. 

The absorption of chloroquine is moderately reduced by magnesium trisilicate and kaolin. Hydroxychloroquine is predicted to be similarly affected. 

Related in vitro studies by the same authors using segments of rat intestine found that the absorption of chloroquine was decreased as follows magnesium trisilicate 31.3%, kaolin 46.5%, calcium carbonate 52%, and gerdiga 36.1%. Gerdiga is a clay containing hydrated silicates with sodium and potassium carbonates and bicarbonates. It is used as an antacid and is similar to attapulgite. ... 

The modest pharmacokinetic interactions between chloroquine and magnesium trisilicate or kaolin are established, but their clinical importance does not seem to have been assessed. One way to minimise any interaction is to separate the dosages of the antimalarials and magnesium trisilicate or kaolin as much as possible (at least 2 to 3 hours) to reduce admixture in the gut. There do not appear to be any studies to see if other antacids behave similarly. 

McElnay JC, Mukhtar HA, D Arcy PF, Temple DJ, Collier PS. The effect of magnesium trisilicate and kaolin on the in vivo absorptionof chloroquine. J Fra MeifTfy (1982) 85,159-63. 

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