Melamine Crystallization: Physicochemical Properties, Interactions With Other Lithogenic Salts and Response to Therapeutic Agents

Abstract

There were reports of children in the People's Republic of China being hospitalized with renal stones and/or failure by September 2008, which were caused by melamine and its co-contaminant cyanurate. We investigated the physicochemical behavior of melamine, its interaction with other endogenous urine factors and the response to therapeutic agents in the renal environment in vitro. A mixed suspension, mixed product removal system was set up for crystallization studies of melamine in urine. Crystallization kinetic parameters, including the nucleation and growth rates, and suspension density, were determined according to crystal number and size, as measured by a Coulter particle counter. Melamine crystallized out from urine under normal urinary conditions (pH 5.0 to 6.5) but crystallization was strongly inhibited at pH 4.5 or lower. Melamine significantly enhanced calcium oxalate precipitation while uric acid significantly decreased melamine crystallization. Bacteria mimicking urinary tract infection promoted melamine crystallization. Clinical relevant drugs, such as citrate and bicarbonate, significantly decreased melamine crystallization. This implies that melamine crystallizes under normal urinary conditions and can interact with other lithogenic salts and pose a significant risk for other stones. Urinary tract infection promotes melamine crystallization. Citrate and bicarbonate therapy are effective prophylactic agents against melamine induced crystallization.