Preservative efficacy in cefuroxime and ceftazidime eye drop formulations

Abstract

The efficacy of various common antimicrobial preservatives was tested in eye drop formulations containing the cephalosporin antibiotics cefuroxime and ceftazidime. The British Pharmacopoeia test for the efficacy of antimicrobial preservatives was used and the formulations were challenged with Staphylococcus aureus, Pseudomonas aeruginosa and Candida albicans. The survival of organisms was monitored over 14 days. Cefuroxime sodium, 50 mg/ml, was studied in simple aqueous solution, and dissolved in an artificial tear formulation, Sno Tears (Smith and Nephew Pharmaceuticals), which contains benzalkonium chloride 0.004% w/v. Ceftazidime (50 mg/ml) was also studied in these two vehicles and, in addition, in a phenylmercuric acetate solution (0.002% w/v) and chlorhexidine acetate (0.02% w/v). Cefuroxime and ceftazidime contributed little, in the short-term, towards a microbicidal preservative effect in the unpreserved aqueous formulations, even against organisms for which they were active. Cefuroxime was adequately preserved in a vehicle of Sno Tears, which contains benzalkonium chloride as the antimicrobial preservative. Ceftazidime was less well preserved in this vehicle, but it was superior to phenylmercuric acetate (0.002% w/v) or chlorhexidine acetate (0.02% w/v).