Precipitate development impedes endophthalmitis treatment effectiveness

HONG KONG — Due to precipitate development that may effectively block up to 94.9% of ceftazidime absorption when mixed with balanced salt solution, one researcher recommended the exploration of the use of newer antibiotics in combination with vancomycin for the treatment of endophthalmitis.

In a presentation here, Mamie Hui, FRCpath, of the department of microbiology at the Chinese University of Hong Kong, said that a checkerboard analysis found ceftazidime concentration fell to 94.9% by 48 hours when mixed with balanced salt solution with or without vancomycin.

Researchers theorized that precipitate formation blocked the absorption of ceftazidime. Dr. Hui performed an equilibrium dialysis study to test this theory. The tests used an equilibrium dialyzer, a simple cylindrical instrument comprised of two chambers separated by a semi-permeable membrane filled with donor vitreous and incubated at 37° C. Ceftazidime and vitreous were added to one chamber and aliquots were taken at regular intervals from the other chamber.

"Ceftazidime concentration fell to an extremely low level at 48 hours," Dr. Hui said. "Such a level may not be sufficient for organisms with high ceftazidime MIC levels, such as Pseudomonas, Acinetobacter, Citrobacter, Enterobacter."

Dr. Hui carried out the same analysis with other gram negative affecting agents. Both ciprofloxacin and amikacin were found to have a much higher concentration at 48 hours (greater than 30%).

Dr. Hui said that while intracameral use of such agents is not commonly practiced, it should be considered in light of this research.

"Loss of antibiotic concentrations is a concern with ceftazidime," she said. "As many newer compounds are coming onto the market, they should be assessed for their potential efficacy in the treatment of endophthalmitis."