For corneal ulcers, what is the recommended initial fluoroquinolone dosing schedule?

• A. Every 2 hours for 24 hours
• B. Every 6 hours
• C. Daily
• D. Every 15 minutes for the first hour

Answer: (D)

Key idea: during a corneal ulcer, the goal is to keep the antibiotic concentration at the corneal surface above the MIC as much as possible in the early hours, because tear turnover and diffusion barriers rapidly reduce drug levels and the infection is aggressive at the site.

Applying a fluoroquinolone every 15 minutes for the first hour achieves a high, sustained concentration right where the bacteria are, increasing the chance that the drug reaches bactericidal levels at the ulcer edge and base. This aggressive initial dosing helps counter rapid drug washout by tears and the potentially high bacterial load, giving the medication a fighting chance to control the infection quickly. After that first hour, the regimen is typically stepped down to maintain exposure, but the crucial immediate period is covered by the very frequent dosing.

In contrast, dosing every 2 hours for 24 hours, every 6 hours, or once daily would leave drug levels subtherapeutic for significant stretches, allowing bacteria to continue multiplying, which can lead to worsening keratitis, larger ulcers, or perforation risk.