Endophthalmitis after intravitreal triamcinolone–moxifloxacin

Kilshor et al.1 recently published a report of 4 cases of acute postoperative endophthalmitis after cataract surgery using prophylaxis with intravitreal triamcinolone–moxifloxacin. This article highlights a very real problem with the intravitreal use of triamcinolone–moxifloxacin. Intravitreal moxifloxacin, in the concentration used in dropless cataract surgery, does not provide adequate prophylaxis against bacteria introduced into the eye during surgery. Our laboratory recently published an experimental study with rabbits2 showing that intravitreal triamcinolone–moxifloxacin does not provide adequate prophylaxis against an intravitreal Staphylococcus aureus challenge. We infected the vitreous in rabbit eyes with clinical endophthalmitis isolates of S aureus with different minimum inhibitory concentrations (MICs) to moxifloxacin (0.032 μg/mL, 2.0 μg/mL, and 10 μg/mL) and immediately treated the eyes with pars plana injections of triamcinolone–moxifloxacin and triamcinolone–moxifloxacin–vancomycin that were equivalent to the human intravitreal doses of the antibiotics. The next day, we examined the eyes for clinical signs of endophthalmitis and cultured the vitreous for viable S aureus.2 Our study indicated that triamcinolone–moxifloxacin intravitreal injection did not prevent endophthalmitis against bacteria with high MICs. After intravitreal triamcinolone–moxifloxacin treatment, all eyes infected with S aureus (MIC = 0.032 μg/mL to moxifloxacin) did not develop endophthalmitis whereas all eyes infected with the S aureus isolates (MIC ≥2.0 μg/mL to moxifloxacin) developed endophthalmitis. Many ophthalmologists favor moxifloxacin because of its penetration into the cornea and anterior chamber; however, many fail to realize its short half-life in the eye. The half-life of moxifloxacin in the vitreous is only 1.72 hours.2–5 In contrast, the half-life of vancomycin is 25.1 hours.2 The initial moxifloxacin concentration of 46.88 μg/mL decreases below 2.0 μg/mL in 8 hours.2 In our laboratory, the MIC90 of S aureus and coagulase-negative Staphylococcus isolated from endophthalmitis ranged from 8 to 16 μg/mL, indicating that the current formulation of triamcinolone–moxifloxacin would be ineffective against the majority of human staphylococcal endophthalmitis isolates.2 In contrast to monotherapy with moxifloxacin, triamcinolone–moxifloxacin–vancomycin prevented endophthalmitis in all eyes infected with S aureus (MIC = 10 μg/mL to moxifloxacin). The vancomycin contained in the formulation was required for preventing endophthalmitis. All 3 S aureus isolates were susceptible to vancomycin (MIC = 2.0 μg/mL).2 A study was presented at the ASCRS meeting in 2014A describing a retrospective chart review of 2300 consecutive eyes that had cataract surgery with transzonular injection of triamcinolone–moxifloxacin.3 There were no cases of postoperative endophthalmitis.3 This study might have provided cataract surgeons with a false sense of security regarding the use of transzonular triamcinolone–moxifloxacin. It is not known whether the eyes of these patients were challenged with bacteria or whether the antibiotic prophylaxis was effective given the low frequency of postoperative endophthalmitis. This study just showed the safety of the formulation. Based on the case reports and the results in our experimental study, the use of intravitreal triamcinolone–moxifloxacin in its current formulation for prophylaxis after cataract surgery might not be effective in preventing endophthalmitis.