Effect of magnesium trisilicate on nitrofurantoin absorption

Area of Science:

• Pharmacology
• Drug Interactions
• Materials Science

Background:

• Nitrofurantoin is a widely used antibiotic for urinary tract infections.
• Antacids are commonly used, and their potential to interact with other medications is a clinical concern.
• Understanding the adsorption properties of antacids is crucial for predicting drug bioavailability.

Purpose of the Study:

• To evaluate the in vitro adsorption of nitrofurantoin by various antacid compounds.
• To assess the in vivo effect of magnesium trisilicate on nitrofurantoin absorption and excretion in humans.

Main Methods:

• In vitro adsorption experiments using nitrofurantoin and several antacid materials (magnesium trisilicate, bismuth oxycarbonate, talc, kaolin, magnesium oxide, aluminum hydroxide, calcium carbonate).
• In vivo study in 6 healthy males involving administration of nitrofurantoin alone versus nitrofurantoin with magnesium trisilicate.
• Measurement of nitrofurantoin excretion in urine to assess absorption rate and extent.

Main Results:

• Magnesium trisilicate demonstrated the highest in vitro adsorption capacity for nitrofurantoin among the tested antacids.
• Co-administration of magnesium trisilicate with nitrofurantoin in vivo resulted in reduced urinary excretion, indicating decreased absorption.
• The duration of nitrofurantoin concentration above the minimum effective concentration (32 µg/ml) was significantly shortened.

Conclusions:

• Magnesium trisilicate effectively adsorbs nitrofurantoin in vitro.
• Concurrent administration of magnesium trisilicate with nitrofurantoin impairs the drug's absorption and reduces its therapeutic window.
• Caution is advised when co-administering nitrofurantoin with magnesium trisilicate to avoid sub-therapeutic drug levels.