Ceftazidime for Gram-negative bacterial keratitis

Empiric keratitis to treat Gram-negative infections is often fortified with tobramycin or monotherapy with fluoroquinolones. Ceftazidime is not generally administered, although it has found success in the past. In this in vitro study, we sought to understand the possible role of ceftazidime in the treatment of Gram-negative keratitis in comparison to other anti-infectives.

This was a retrospective study at an academic tertiary care ophthalmology department. The laboratory records of patients with culture-positive Gram-negative keratitis were evaluated for anti-infective susceptibility of Gram-negative bacteria to ceftazidime, tobramycin, ciprofloxacin, and polymyxin B. The median minimum inhibitory concentration (MICs μg/ml) of each Gram-negative bacterial group was compared to the established serum standards.

Analysis of Pseudomonas aeruginosa isolates from 38 patients between January 1, 2020, and December 31, 2021, demonstrated median MICs for four antibiotics: ceftazidime (1.5 μg/ml), tobramycin (1.5 μg/ml), ciprofloxacin (0.094 μg/ml), and polymyxin B (1.75 μg/ml). Among 15 isolates from other Gram-negative isolates during the same period, the median MICs were: ceftazidime (0.19 μg/ml), tobramycin (1.0 μg/ml), ciprofloxacin (0.032 μg/ml), and polymyxin B (1.0 μg/ml). All median MIC values for P. aeruginosa and other Gram-negative bacteria were denoted as susceptible, as interpreted by the serum standards.

Based on in vitro testing, our data suggest that ceftazidime may still be useful in the treatment of Gram-negative keratitis. Patient comfort, costs, and availability will dictate the role of ceftazidime in the treatment of Gram-negative keratitis.