In vitro adsorption of lithium by bentonite

Lithium poisoning is currently managed using a combination of supportive care and urgent haemodialysis in severe cases. Activated charcoal as a gut decontaminant has been found to be ineffective. The use of Sodium Polystyrene Sulphonate (SPS) as an adsorbent has been found to be effective in some studies. However, there have been case reports of gut necrosis and perforation occurring when SPS was used for the treatment of hyperkalaemia in post operative patients or patients with renal failure. Bentonite is a known adsorbent that has been used in the management of paraquat poisonings. The purpose of this study was to determine the ability of bentonite to adsorb lithium.

4.5 g of lithium carbonate was dissolved in 1.5 L of deionised water to form the stock solution. 50 mL aliquots of this stock solution were added to 50 mL of either distilled deionised water (pH 7) or simulated gastric fluid (pH 1.2). Bentonite of either 0.75, 1.5 or 4.5 g was then added to simulate 5:1, 10:1 and 30:1 ratio of adsorbent-to-drug. Controls were made with no bentonite added. The resulting mixture was placed on a shaker for five minutes before being filtered. The filtrate was diluted and batch analysed for lithium using atomic absorption spectrophotometry.

Bentonite decreased the concentration of lithium recovered from the filtrate by 20.55% in deionised water compared to 48.09% in simulated gastric fluid at a bentonite:lithium ratio of 30:1 (p value 0.005).

This study shows that bentonite is an effective adsorbent for lithium. The effect is enhanced in simulated gastric fluid. In vivo studies are being planned for clinical correlation.