Comparison between intracameral moxifloxacin administration methods by assessing intraocular concentrations and drug kinetics

Studies have indicated that intracameral administration of moxifloxacin (MFLX), a fourth-generation fluoroquinolone, is safe and effective. However, administration methods vary between studies, and no definite protocol exists. A prospective study clarifying the incidence of endophthalmitis and complication rates associated with each administration method would require an extremely large sample size because endophthalmitis has a low incidence rate. Therefore, we investigated appropriate intracameral MFLX administration methods by assessing intraocular concentrations following simple injection and flushing, and by measuring drug kinetics (half-life). Experiment 1: (human eyes). Irrigation (flushing) with 33.33 μg/ml MFLX (150-fold dilution) and simple injection with 0.1 ml of 500 μg/ml MFLX (10-fold dilution) were assessed after cataract surgery. Experiment 2: (rabbits: kinetics study). Flushing with 30-fold or 150-fold dilutions of MFLX was assessed. Aqueous humor samples (0.1 ml) obtained immediately after irrigation and 1, 3, and 5 h after irrigation were analyzed using high-performance liquid chromatography. Experiment 1: MFLX (500 μg/ml) administered using simple injection in humans underwent a 3.3-fold dilution (152.33 μg/ml). Total anterior chamber displacement after flushing with 33.33 μg/ml MFLX resulted in a concentration of 29.54 μg/ml (90 % displacement). Experiment 2: Concentrations at baseline were 52 % at 1 and 15 % at 3 h respectively, suggesting that the half-life of intracameral MFLX was >1 h. Considering that the half-life of MFLX was >1 h, a final concentration of 150 μg/ml results in a 2 h concentration of 38 μg/ml, which was beyond the minimum inhibitory concentration required to inhibit the growth of 90 % of bacteria (MIC90) for most resistant pathogens. We postulate that a final concentration of 150 μg/ml is considerably effective and safe. However, more resistant bacteria will evolve in the future, and the standard MIC90 may change accordingly. Therefore, even if a suitable concentration is determined, it may not necessarily remain constant. This effective concentration should be continually revised on the basis of safety and effectiveness assessments.