Enteric-coated solid dosage forms containing sodium bicarbonate as a drug substance: an exception from the rule?

Abstract

Sodium bicarbonate (sodium hydrogen carbonate) is used as an oral medication in disorders such as mild metabolic acidosis and chronic kidney disease. The two commercial products on the German market, bicaNorm and Nephrotrans, and also newly developed multiple-unit pellet formulations, have been characterized in these investigations by in-vitro methods like disintegration and dissolution testing. Both marketed products containing sodium bicarbonate are of sufficient pharmaceutical quality according to the European Pharmacopoeia. However, they and the novel pellet preparations showed different drug release at moderately elevated pH values. Early drug release may cause dose dumping in the stomach and adverse drug effects from the developed carbon dioxide. The soft capsule preparation (Nephrotrans) released the smallest amount of sodium bicarbonate at pH 1 and 4.5 of all formulations tested. It appeared that oral dosage formulations of sodium bicarbonate were an exception to the rule: the monolithic soft capsule seemed to be superior to an enteric-coated tablet as well as to multiple-unit pellet formulations from the biopharmaceutical point of view. Our results correspond with individual reports on adverse effects from patients treated with the sodium bicarbonate products.