Inhibition of bacterial growth by the nitrofurantoin solvent dimethylformamide

For quantitative susceptibility tests, stock solutions of nitrofurantoin are often prepared in dimethylformamide. Since 1.0 or 2.0 ml of the solvent will inhibit microbial growth, currently recommended procedures for antimicrobic dilution tests should be modified by adding only 0.1 or 0.2 ml of stock drug solutions to the agar or broth medium.