Nitrofurantoin solubility in aqueous urea and creatinine solutions.

Experiments were carried out to determine the effect of urea and creatinine on the solubility of nitrofurantoin in water at different temperature and pH conditions. The addition of urea to aqueous media increased nitrofurantoin solubility up to a maximum concentration level and then decreased solubility at higher urea concentrations. The amount of urea needed to bring about maximum nitrofurantoin solubility was dependent on temperature and ranged between 1.75 and 2.50%. Spectral studies suggest a possible interaction between urea and nitrofurantoin molecules. Nitrofurantoin solubility increased with an increasing creatinine concentration ranging from 0.05 to 1.6%. Spectral studies indicate a strong interaction between creatinine and nitrofurantoin molecules in solution. The combined effect of urea and creatinine of the solubility of nitrofurantoin could account for the absence of crystalluria with this drug, even though unusually high concentrations in urine have been reported.