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


METHODS
Extemporaneous formulations of eye drops were prepared from a commercially-available parenteral product of cefazolin sodium: eye drops 'A' contained 50mg/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.


RESULTS
The eye drops stored at 4 degrees 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.


CONCLUSIONS
Extemporaneously prepared formulations of cefazolin are unstable at room temperature and should be stored in a refrigerator.
National University Hospital, Singapore.
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D001431:Bacteriological Techniques; D002437:Cefazolin / Q000032:analysis*; D002511:Cephalosporins / Q000032:analysis*; D004355:Drug Stability; D004356:Drug Storage; D006863:Hydrogen-Ion Concentration; D009883:Ophthalmic Solutions / Q000032:analysis*; D009994:Osmolar Concentration; D011310:Preservatives, Pharmaceutical; D013696:Temperature
D002511:Cephalosporins; D009883:Ophthalmic Solutions; D011310:Preservatives, Pharmaceutical; D002437:Cefazolin