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A spectrophotometric assay method for the quantitative determination of amikacin, kanamycin, neomycin, and tobramycin in pharmaceutical dosage forms has been developed. The method is based on the Hantzsch reaction, forming dihydrolutidine derivatives which can be measured spectrophotometrically. The excipients EDTA, phenol, sodium bisulfite, and sodium citrate do not interfere, while salts of ammonia do interfere. The relative standard deviations based on seven readings were 1.64, 1.88, 2.10, and 1.93% for amikacin, kanamycin, neomycin, and tobramycin, respectively. Assay results have been compared with microbiological assay results provided by the manufacturers. The assay method appears to be stability indicating.

The chemical stabilities of metronidazole (in water) and ten antibiotics (ampicillin, carbenicillin, cefamandole, cefazolin, cefoxitin, moxalactam, nafcillin, penicillin G, piperacillin, and ticarcillin) in 5% dextrose injection (except ampicillin which was in 0.9% sodium chloride) with magnesium sulphate were studied at 25 degrees C. The clarity of the solutions did not change in 20 h. The pH values of metronidazole, nafcillin and penicillin G solutions containing magnesium sulphate were lower (at 0 and 20 h) by up to 1.2 units as compared with solutions without magnesium sulphate. The decomposition of nafcillin and penicillin G solutions was hastened significantly by magnesium sulphate due to effect on the pH values of the solutions.