The Role of Intracameral Moxifloxacin in Drop-Free Cataract Surgery

Drop-free cataract surgery was introduced to reduce the burden of medications, medication administration errors, adherence problems, and possibly the costs associated with conventional postoperative topical regimens by delivering some or all required medications intraoperatively. It has not escaped surgeons that promoting a drop-free approach can also offer a competitive advantage.

Antibiotic prophylaxis, the suppression of postoperative inflammation, and the prevention of cystoid macular edema are distinct therapeutic objectives, each with its own risk-benefit profile. For antibiotic prophylaxis, the focus of this article, intraocular drug delivery offers more than convenience. An intracameral antibiotic injection can achieve an immediate, reproducible, high drug concentration in the anterior chamber at the moment bacterial contamination is most likely to have occurred, and it avoids the variable corneal penetration, delayed administration, and imperfect patient compliance associated with topical antibiotics.

Do supplemental topical antibiotic drops, however, add safety to intracameral administration?

From Vancomycin and Cefuroxime to Moxifloxacin

During the 1990s and early 2000s, intracameral vancomycin and cefuroxime were the principal choices for postoperative endophthalmitis prophylaxis. Vancomycin offered strong gram-positive coverage but was limited by antimicrobial-stewardship concerns and, later, by recognition of the rare but devastating possibility of hemorrhagic occlusive retinal vasculitis.^1,2 Cefuroxime, first proposed in Sweden,³ gained stronger clinical support with the ESCRS trial⁴ but remained vulnerable to preparation and dilution errors where a licensed single-dose product was unavailable, and it is ineffective against enterococci.⁵

During the past 2 decades, intracameral moxifloxacin has emerged as an attractive alternative to vancomycin and cefuroxime. Compared to those drugs, moxifloxacin has a broader spectrum, it offers concentration-dependent bactericidal activity, and it is available in preservative-free ophthalmic formulations.⁶ Its clinical effectiveness is supported most notably by a registry of 2,062,643 consecutive cataract operations in which intracameral moxifloxacin was associated with a reduction in the rate of postoperative endophthalmitis from 0.07% to 0.02%. In eyes complicated by posterior capsular rupture, the rate declined from 0.43% to 0.18%.⁷ The principal safety concerns are bilateral acute iris transillumination (BAIT) and bilateral acute depigmentation of the iris (BADI) syndromes from excessive dosing or preparation errors⁸ and toxic anterior segment syndrome from formulations containing harmful excipients such as xanthan gum.^9,10 When an appropriate preservative-free formulation is correctly prepared, dosed, and administered, clinically significant ocular toxicity appears to be extremely uncommon.

What the Pharmacokinetics Say

Pharmacokinetic modeling suggests that a retained moxifloxacin dose of 500 to 600 μg may remain above the minimum inhibitory concentration required to inhibit 90% of isolates (MIC90) for most susceptible organisms for approximately 36 to 37 hours, with modeled bactericidal protection extending to approximately 39 to 40 hours when a 3-hour postantibiotic effect is included (Figure 1).¹¹ For the most resistant reported staphylococcal isolates (eg, coagulase-negative staphylococci with a maximum reported MIC of 64 μg/mL),¹² the duration of protection is substantially shorter. These estimates underscore the importance of achieving a high early concentration during the window when organisms introduced at surgery may begin to proliferate.

Figure 1. Modeled anterior chamber (AC) concentrations following intracameral (IC) administration of the time-dependent antibiotics cefuroxime or vancomycin (1,000 μg) and the concentration-dependent antibiotic moxifloxacin (500 μg). Horizontal reference lines indicate MIC90 values of 2 μg/mL for coagulase-negative staphylococci (CoNS) treated with cefuroxime or vancomycin and 0.06 μg/mL for methicillin-susceptible Staphylococcus aureus (MSSA) treated with moxifloxacin in the Antibiotic Resistance Monitoring in Ocular Microorganisms (ARMOR) study. The highest reported moxifloxacin MICs - 32 μg/mL for methicillin-resistant S aureus (MRSA) and 64 μg/mL for CoNS - are also shown. The curves extend to the relevant 2 μg/mL CoNS and 0.06 μg/mL MSSA thresholds. Shaded areas represent the modeled duration of effective activity above these thresholds; the moxifloxacin region includes an assumed postantibiotic effect of approximately 3 hours, based on the fluoroquinolone pharmacodynamic literature.

Getting the Dose Into the Eye

Our initial guidance recommended approximately 450 to 600 μg delivered in a relatively large volume of 0.3 to 0.4 mL after the main incision was sealed.^13,14 The nominal dose drawn into the syringe must exceed the intended retained dose because some of the mixed, drug-containing anterior chamber fluid exits through the surgical incision during injection. The exact dynamics depend on the volumes of the anterior chamber and the capsular bag, the homogeneity of solution mixing, and errors in the volume delivered by the syringe. A simple working assumption is that the injected volume roughly equals the leaked, well-mixed volume. Models that account for this leakage have suggested that injecting 0.55 mL at a concentration of 150 μg/0.1 mL leaves 500 μg - the target retained dose - in the eye at the conclusion of surgery (Figure 2).¹⁵

Figure 2. Predicted final AC drug mass as a function of injected volume at three prepared moxifloxacin concentrations, modeled for solution mixing and aqueous humor leakage.

Figure 2 illustrates that a small, concentrated 0.1-mL bolus delivered straight from the bottle produces a very steep curve that is highly sensitive to small injected volume errors common with small syringes. Additionally, injecting a highly concentrated solution can create transient areas of very high local drug concentration, which may cause BAIT or BADI, particularly in phakic eyes where the iris is closely apposed to the crystalline lens or a phakic IOL. Conversely, injecting a nominal 500 μg in a large volume without accounting for intraoperative leakage yields a residual dose below target; increasing the injected volume brings the retained dose progressively closer to, but never reaches, the 500-μg target in the model.

Can Topical Supplementation Add Anything?

Modeling suggests that, once an effective intracameral dose has been delivered, the postoperative administration of topical moxifloxacin confers an additional benefit only after approximately the first 18 hours. Modeling of combined intracameral and topical administration (Figure 3) indicates that the intracameral injection supplies the dominant antimicrobial exposure during the immediate postoperative period. Topical moxifloxacin appears to contribute relatively little while intracameral concentrations remain high; the principal role of the topical drug is to extend antimicrobial coverage after the intracameral concentration has substantially declined. Topical supplementation every 6 hours keeps the anterior chamber moxifloxacin concentration high enough to eliminate all but the few most resistant pathogenic strains ever reported for as long as the topical coverage continues.¹⁶

Figure 3. Modeled AC moxifloxacin concentrations after IC injection alone (blue; same as Figure 1) or with topical moxifloxacin 0.5% every 1 hour (red), every 4 hours (orange), or every 6 hours (brown). IC treatment dominates early exposure; topical supplementation extends coverage as IC levels decline. Horizontal lines indicate the MSSA mutant prevention concentration (MPC; 0.6 mg/L) and MIC90 (0.06 mg/L).

At our center and at Laval University in Quebec City, Canada, intracameral moxifloxacin supplemented with topical moxifloxacin has achieved a postoperative infection rate below one in 20,000; to our knowledge, this is the lowest rate reported to date.¹⁷ In our view, adjunctive topical therapy is reasonable when the retained intracameral dose is uncertain, when wound integrity is in question (eg, a patient who might rub their eye), or when surgical complications increase the risk of infection.

Where This Leaves Us

The practical value of drop-free cataract surgery is in reducing avoidable treatment burden while maintaining reliable prophylaxis. Intracameral antibiotics deliver immediate, high intraocular concentrations and minimize dependence on patient adherence. That said, the effectiveness and safety of intracameral prophylaxis depend on the specific formulation, dose, preparation technique, and injection method.¹⁸ Preservatives, contamination, incorrect dilution, or the use of a formulation not suitable for intraocular administration may cause toxic anterior segment injury.

Based on existing susceptibility data and mathematical modeling, we propose a retained target dose of approximately 500 μg,^8,14 delivered by a large-volume intracameral injection (0.55 mL at 150 μg/0.1 mL) at the end of surgery, as the most reproducible modeled method of providing strong early antimicrobial protection.^14,15 A commercial preparation at this concentration, supplied in 0.75-mL syringes for intracameral injection, is available in Canada from Aved; its development was presented at the 2026 Canadian Ophthalmological Society Annual Meeting in Montreal.

Postoperative endophthalmitis is a rare but devastating complication of cataract surgery. Prolonged supplemental topical antibiotic therapy adds protection - particularly if the patient rubs the operative eye or a surgical complication raises the risk of infection.