Intravitreal vancomycin and gentamicin concentrations in patients with postoperative endophthalmitis

Background/aims-To study the intravitreal antibiotic concentrations and the efficacy of an intravitreal dosing regimen to treat patients with postoper ative bacterial endophthalmitis. This regimen, based on pharmacokinetic/pha rmacodynamic considerations, relies on a repeat antibiotic injection of a l ower dose than is generally used. Methods-In consecutive patients with suspected postoperative endophthalmiti s a vitreous biopsy for bacterial culture was taken before 0.2 mg vancomyci n and 0.05 mg gentamicin were injected intravitreally. After 3 or 4 days a second biopsy was taken for bacteriological culture and to measure intravit real vancomycin and gentamicin concentrations, followed by a repeat injecti on of 0.2 mg vancomycin. Results-17 patients entered the study. In 11 patients the initial bacterial culture was positive, predominantly coagulase negative staphylococci. All second vitreous biopsies were sterile. Intravitreal vancomycin levels varie d between 2.6 and 18.0 mug/ml (mean 10.3 (SD 4.1) mug/ml) after 3 days and between 3.1 and 16.6 mug/ml (mean 7.5 (6.2) mug/ml) after 4 days which is w ell above the minimal inhibitory concentration for most micro-organisms. Co ncentrations of intravitreal gentamicin varied between 0.90 and 3.3 mug/ml (mean 1.6 (0.72) mug/ml) after 3 days and between 1.2 and 2.6 mug/ml (mean 1.9 (0.99) mug/ml) after 4 days. Conclusion-This dosing regimen resulted both in adequate intravitreal vanco mycin and gentamicin levels for over a week as well as in negative second c ultures. This study also provides new information on intravitreal vancomyci n and gentamicin concentration over time in patients with postoperative end ophthalmitis.