What are the concentrations of fortified Vancomycin (vancomycin) and Tobramycin (tobramycin) for corneal ulcer treatment?

From the Guidelines

For corneal ulcers, fortified vancomycin is typically prepared at a concentration of 25-50 mg/mL (2.5-5%), while fortified tobramycin is usually prepared at 14 mg/mL (1.4%). These concentrated formulations are used because standard commercial antibiotic eye drops often don't achieve sufficient drug levels to effectively treat severe corneal infections.

Key Considerations

• Fortified antibiotics are typically administered every 30-60 minutes initially, then gradually tapered as the infection improves.
• These medications are usually prepared by hospital pharmacies since they're not commercially available in these concentrations.
• Treatment should be initiated promptly after corneal cultures are obtained.
• The combination of vancomycin (which targets gram-positive organisms including MRSA) and tobramycin (effective against gram-negative bacteria) provides broad-spectrum coverage until culture results guide more targeted therapy.
• Patients should be monitored closely for clinical improvement, and treatment may need adjustment based on clinical response and culture results, as indicated by recent studies 1.

Rationale

The use of fortified antibiotics for corneal ulcers is supported by recent guidelines and studies, which emphasize the importance of achieving high tissue levels of antibiotics to effectively treat severe corneal infections 1. The preparation of fortified vancomycin and tobramycin at specific concentrations is crucial to ensure optimal therapeutic benefits.

Administration and Monitoring

• The administration of fortified antibiotics should be guided by the severity of the infection and the patient's response to treatment.
• Close monitoring of the patient's clinical improvement and adjustment of treatment based on culture results are essential to ensure effective management of corneal ulcers, as highlighted in recent studies 1.

From the FDA Drug Label

DESCRIPTION: Tobramycin ophthalmic solution USP, 0.3% is a sterile topical ophthalmic antibiotic formulation prepared specifically for topical therapy of external ophthalmic infections. Each mL of tobramycin ophthalmic solution USP, 0.3% contains:Active: tobramycin 0.3 % (3 mg). The concentration of tobramycin for corneal ulcer is 0.3% (3 mg/mL).

• There is no information about the concentration of fortified vancomycin in the provided drug label. 2

From the Research

Concentration of Fortified Vancomycin and Tobramycin for Corneal Ulcer

• The concentration of fortified tobramycin and vancomycin for corneal ulcers is not explicitly stated in the provided studies 3, 4, 5, 6, 7.
• However, study 5 mentions that the dosing schedule for fortified tobramycin-cefazolin included 1.3% tobramycin and 5.0% cefazolin.
• Study 6 suggests using a combination of antibiotics including cefazolin and tobramycin or gentamicin, but does not specify the concentration.
• Study 7 compares the use of fluoroquinolone drops with combined fortified antibiotics (tobramycin 1.3%-cefazolin 5%) for treating bacterial corneal ulcers.
• It is worth noting that the concentration of fortified vancomycin and tobramycin may vary depending on the specific treatment protocol and the severity of the corneal ulcer, as mentioned in study 3.

Treatment Protocols

• Study 3 describes a treatment protocol that includes hourly fortified tobramycin and vancomycin eye drops, as well as tobramycin-soaked collagen shields.
• Study 5 outlines a dosing schedule for fortified tobramycin-cefazolin that includes 1 to 2 drops every 30 minutes for 6 hours, then hourly for the remainder of day 1.
• Study 7 compares the clinical efficacy of fluoroquinolone drops with combined fortified antibiotics (tobramycin 1.3%-cefazolin 5%) and finds that monotherapy with fluoroquinolone eye drops leads to shorter duration of intensive therapy and shorter hospital stay.