Tobramycin is the most commonly used fortified antibiotic for sight-threatening ocular infections. Which of the following represents this fortified agent?

• A. Cefazolin Alone
• B. Vancomycin
• C. Tobramycin
• D. Gentamicin

Answer: (C)

Fortified topical antibiotics are high-concentration preparations used to achieve bactericidal levels in the cornea and anterior chamber for sight-threatening infections. The most commonly used fortified agent is tobramycin, prepared at a high dose (often around 14 mg/mL) to maximize coverage against gram-negative bacteria, including Pseudomonas. It’s typically used in combination with another antibiotic (such as cefazolin) to provide broad-spectrum coverage, especially for severe keratitis or endophthalmitis.

So, the fortified agent described here is tobramycin. Cefazolin alone provides gram-positive coverage but is not the fortified agent by itself; vancomycin and gentamicin can be used in fortifications in certain scenarios, but tobramycin is the standard first choice for sight-threatening cases.