A stability-indicating HPLC assay method has been developed to quantify metronidazole benzoate in suspensions. A study of the stabilities of two suspensions (16.0 mg/ml) of metronidazole benzoate in commercially available vehicles, Ora-Plus and a mixture of Ora-Plus and Ora-Sweet, showed that both suspensions were stable for at least 90 days at room temperature. The mobile phase required to elute metronidazole benzoate contained 40% acetonitrile versus approximately 10% for the free base. The solubility of the ester in water at 25 degrees C was found to be approximately 0.1 mg/ml versus 10 mg/ml for the free base. The ester did not hydrolyse significantly to the free base after storage for 8 h at 37 degrees C in simulated gastric fluid, and 5 h at 37 degrees C in simulated intestinal fluid. The bitter tasting metronidazole may not be satisfactorily substituted with its tasteless ester in the treatment of local gastrointestinal infections.

Levothyroxine sodium tablets from two different manufacturers were analysed using the USP-NF method of analysis, a stability-indicating high pressure liquid chromatographic (HPLC) procedure. The results indicate that one particular manufacturer's 0.2-mg pink tablets contain some excipient(s) which act as a catalyst to hasten decomposition after extraction of levothyroxine for analysis. The same tablets from a different batch showed an additional long peak in the chromatogram, which indicated that the excipient(s) may have been changed. The same manufacturer has also used three different types of bottles/lids for the same product during the last year. Good manufacturing practice requires that new compatibilities/stability studies be conducted to assure the quality of the product. Ongoing stability studies are required by the Food and Drugs Administration (FDA). The use-life of 0.2-mg pink tablets of this manufacturer may be short.

A stability-indicating high performance liquid chromatographic method has been proposed to quantify captopril. The method has been used to determine the stability of captopril in oral liquid dosage forms prepared from either commercially available tablets or powder. The dosage forms in water were more stable than when the vehicle was a syrup. Furthermore, the dosage form prepared using powder in water was more stable than when tablets were used. While the decomposition of captopril followed first-order equation when the dosage forms were prepared in syrup (in two of the three solutions studied), this equation was not followed when water was the vehicle. This is probably due to an uncontrolled factor, oxygen, because captopril is very sensitive to oxidation. Captopril solution prepared in water using tablets was stable for about 20 days when stored at 5 degrees C, and that prepared using powder in water was stable for about 27 days. One commercial syrup hastened the process of decomposition with an additional unidentified product of decomposition.

The chemical stabilities of cefoperazone and ceftazidime solutions in 5% dextrose and 0.9% sodium chloride injections have been studied using high-performance liquid chromatography methods. The solutions of cefoperazone were stable for 8 days (loss in potency of less than 10%) at 25 degrees C, for at least 80 days at 5 degrees C and for at least 96 days at -10 degrees C. The ceftazidime solutions were stable for only 2 days at 25 degrees C, for 21 days at 5 degrees C (28 days in normal saline) and for 90 days at -10 degrees C. Thawing the frozen solutions using a microwave oven did not cause degradation.

The stability of piperacillin sodium in the presence of tazobactam sodium in 5% dextrose and normal saline i.v. admixtures has been determined using a modified stability-indicating high performance liquid chromatography assay method reported in the literature. The solutions were stored at room and refrigerator temperatures in plastic bags. They remained clear throughout the study although the pH values decreased slightly during storage. The solutions were stable for 2 days at 25 degrees C and for 28 days at 5 degrees C. Tazobactam sodium appears to have a slight adverse effect on the stability of piperacillin sodium.