Aluminium magnesium trisilicate

Antacids are basic substances that reduce gastric acidity by neutralising HCl. The hydroxide is the most common base but trisilicate, carbonate and bicarbonate are also used. Therapeutic efficacy and adverse effects depend also on the metallic ion with which the base is combined, and this is usually aluminium, magnesium or sodium. Calcium and... 

Antacids, particularly aluminium hydroxide gel, magnesium trisilicate, and sodium bicarbonate, reduce the systemic availability of rifampicin (97). 

Figure 6.20 Adsorption of digoxin by some antacids at 37 0.1°C ( ) magnesium trisilicate, (A) aluminium hydroxide gel BP (Aludrox was used in the concentration range 2.5-10%v/v), (A) light magnesium oxide, (O) light magnesium carbonate, ( ) calcium carbonate. Initial concentration of the glycoside 0.25 mg%.

Figure 10.16 Adsorption of digoxin from Lanoxin paediatric elixir at 37 0.1 °C by , Aluminium Hydroxide Gel BP (10% v/v) A, Magnesium Trisilicate Mixture BPC (10% v/v) A, Gelusil suspension (10% v/v) , Lanoxin elixir diluted 1 10 with water.

Gaviscon aluminium hydroxide calcium carbonate magnesium hydroxide magnesium trisilicate sodium bicarbonate. 

Table 176 shows how it was possible to considerably improve the tabletting properties of an antiacid tablet containing alginic acid, magnesium trisilicate, aluminium hydroxide and sodium hydrogen carbonate as the active principles by the addition of copovidone. The hardness was doubled and the friability reduced by half. 

Magnesium carbonate halves the maximum plasma levels of halofantrine, which may be clinically relevant. Aluminium hydroxide and magnesium trisilicate seem less likely to interact. 

Magnesium carbonate might decrease the absorption of halofantrine. In vitro study showed that the halofantrine absorptive eapaeity of various antacids was highest for magnesium carbonate, intermediate for aluminium hydroxide, and least for magnesium trisilicate. ... 

In vitro tests showed that magnesium trisilicate adsorbed proguanil. Two other antacids, aluminium hydroxide and light magnesium carbonate,... 

Magnesium trisilicate reduces the absorption of nitrofurantoin, but the cUnical significance of this is unknown. Aluminium hydroxide is reported not to interact with nitrofurantoin. Whether other antacids interact adversely is uncertain. 

Magnesium trisUicate 5 g in 150 mL of water reduced the absorption of a single 100-g oral dose of nitrofurantoin in 6 healthy subjects by more than 50%. The time during which the concentration of nitrofurantoin in the urine was at, or above 32 micrograms/rtiL (a level stated to be the minimum inhibitory concentration) was also reduced. The amounts of nitrofurantoin adsorbed by other antacids in in vitro tests were as follows magnesium trisilicate and charcoal 99%, bismuth subcarbonate and talc 50 to 53%, kaolin 31%, magnesium oxide 27%, aluminium hydroxide 2.5% and calcium carbonate 0%. ... 

It is not yet known whether magnesium trisilicate significantly reduces the antibacterial effectiveness of nitrofurantoin but the response should be monitored. While it is known that the antibacterial action of nitrofurantoin is increased by drugs that acidify the urine (so that reduced actions would be expected if the urine were made more alkaline by antacids) this again does not seem to have been confirmed. The results of the in vitro studies suggest that the possible effects of the other antacids are quite small, and aluminium hydroxide is reported not to interact. 

When 5 healthy subjects took a single 600-mg dose of rifampicin with various antacids the absorption of rifampicin was reduced. The antacids caused a fall in the urinary excretion of rifampicin as follows 15 or 30 mL of aluminium hydroxide gel 29 to 31% 2 or 4 g of magnesium trisilicate 31 to 36% and 2 g of sodium bicarbonate 21%. ... 

It has been suggested that the rise in stomach pH caused by these antaeids reduces the dissolution of the rifampicin and thereby inhibits its absorption. In addition, aluminium ions may form less soluble ehelates with rifampicin, and magnesium trisilicate can adsorb rifampicin, both of which would also be expected to reduce bioavailability. ... 

The absorption of valproate was slightly, but not significantly, increased by an aluminium/magnesium hydroxide suspension but not by magnesium trisilicate or a calcium carbonate suspension. 

Antacids containing aluminium/magnesium hydroxide or magnesium trisilicate can reduce the serum levels of chlorpromazine which would be expected to reduce the therapeutic response. Sucralfate and an aluminium/magnesium hydroxide antacid can reduce the absorption of sulpiride. In vitro studies suggest that this interaction may possibly also occur with other antacids and phe-nothiazines. There seem to be no clinical studies or reports confirming the anecdotal evidence of a possible reduction in the effects of haloperidol by antacids. 

Aluminium hydroxide gel 30 mL did not affect the plasma level of a single 40-mg dose of propranolol in 6 healthy subjects the reduction in exercise heart rate was also unaffected. In contrast, a study in 5 healthy subjects found that 30 mL of an aluminium hydroxide gel reduced the levels and AUC of a single 80-mg dose of propranolol by almost 60%. In vitro and animal data suggest that bismuth subsalicylate, kaolin-pectin and magnesium trisilicate can also reduce the absorption of propranolol. ... 

Other studies describe reductions in digoxin absorption of 11% with aluminium hydroxide, 15% with bismuth carbonate and light magnesium carbonate, and 99.5% with magnesium trisilicate. ... 

Evidence of no interaction. A study in 4 patients chronically treated with digoxin 250 to 500 micrograms daily, found that the concurrent use of either 10 mL of aluminium hydroxide mixture BP or magnesium trisilicate mixture BP, three times daily, did not reduce the bioavailability of the digoxin and none of the patients showed any reduction in the control of their symptoms. ... 

The absorption of prednisone, and probably prednisolone, can be reduced by lai e but not small doses of aluminium/magnesium hydroxide antacids. Dexamethasone absorption is reduced by magnesium trisilicate. 

---