Stability of cefazolin sodium eye drops

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Assessing the stability of cefazolin sodium in preservative-free and preservative-containing eye drops.


Extemporaneous formulations of eye drops were prepared from a commercially-available par enteral product of cefazolin sodium: eye drops ‘A’ contained 50 mg/ml of cefazolin sodium in 0•45% w/v sodium chloride solution, and eye drops ‘B’ contained 50 mg/ml, 0•005% w/v thiomersal and 1% w/v glycerol in water-for-injection. Cefazolin sodium concentrations in these eye drops were monitored by a stability-indicating HPLC assay method. Measurements of pH and osmolality, as well as tests for microbial contamination, were conducted.


The eye drops stored at 4 °C were stable for 42 days with minimal changes in pH and osmolality, but eye drops stored at room temperature were only stable for a few days with greater increments in pH and osmolality. None of the samples cultured had bacterial or fungal growth after 7 days of incubation.


Extemporaneously prepared formulations of cefazolin are unstable at room temperature and should be stored in a refrigerator.

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