What is the recommended dose of tobramycin (an aminoglycoside antibiotic) eye drops for an adult patient with a bacterial eye infection?

Tobramycin Eye Drops Dosing

For mild to moderate bacterial conjunctivitis, instill 1-2 drops of tobramycin 0.3% into the affected eye(s) every 4 hours for 7 days, while for severe infections, instill 2 drops hourly until improvement, then taper before discontinuation. 1

Standard Dosing by Severity

Mild to Moderate Bacterial Conjunctivitis

• Instill 1-2 drops of tobramycin 0.3% every 4 hours (approximately 4-6 times daily) for 5-7 days 1, 2
• Enhanced viscosity formulations may be dosed twice daily with equivalent efficacy to standard four-times-daily regimens 3
• The 5-7 day course accelerates clinical and microbiological remission, reduces transmissibility, and allows earlier return to work/school 2

Severe Bacterial Conjunctivitis

• Instill 2 drops hourly until clinical improvement is observed, then reduce frequency prior to discontinuation 1
• Obtain conjunctival cultures and Gram staining before initiating treatment if severe purulent discharge is present 4, 2

Bacterial Keratitis (Corneal Ulcer) Dosing

Severe/Central Keratitis

• Loading dose: 1-2 drops every 5-15 minutes for the first 6 hours 5
• Day 1: Continue hourly for remainder of day after loading dose 5
• Days 2-3: Every hour around the clock 5
• Days 4-5: Every 2 hours 5
• Days 6-14: Every 4 hours, then taper based on clinical response 5
• Treatment may need to continue for 2 weeks or longer with gradual tapering 5

Fortified Tobramycin Preparation

• For severe corneal infections requiring higher concentrations, prepare fortified tobramycin 14 mg/mL by adding 2 mL of intravenous tobramycin (40 mg/mL) to a 5-mL bottle of tobramycin 0.3% ophthalmic solution 5, 2
• Refrigerate and shake well before each instillation 5
• Use the same dosing frequency as standard severe keratitis regimen 5

Blepharitis Dosing

• Apply tobramycin to eyelid margins one or more times daily or at bedtime for a few weeks 2, 5
• Frequency and duration should be guided by severity and response to treatment 2
• Consider combination therapy with tobramycin/dexamethasone for blepharoconjunctivitis 2

Critical Dosing Considerations

Tapering and Duration

• Never taper below 3-4 times daily, as subtherapeutic doses increase antibiotic resistance risk 2
• Prolonged use can cause medication toxicity manifesting as worsening inflammation or corneal melting 2
• Taper gradually as infection improves based on clinical response 2

Monitoring Clinical Response

• Positive response indicators include: reduced pain and discharge, lessened eyelid edema or conjunctival injection, sharper demarcation of stromal infiltrate perimeter, and initial re-epithelialization 2
• Advise patients to return for follow-up if no improvement after 3-4 days of treatment 2

Important Pitfalls and Caveats

When Tobramycin May Be Insufficient

• Gonococcal conjunctivitis requires systemic antibiotic therapy (ceftriaxone 1g IM plus azithromycin 1g orally), not topical treatment alone 2
• Chlamydial conjunctivitis requires systemic antibiotics (oral erythromycin or azithromycin), as topical therapy is insufficient 2
• MRSA conjunctivitis may require compounded topical vancomycin, as MRSA is resistant to aminoglycosides including tobramycin 2
• Contact lens wearers with suspected Pseudomonas infection should receive fluoroquinolones rather than tobramycin 2

Resistance Concerns

• In neonatal intensive care settings, gram-negative conjunctivitis is often resistant to gentamicin (and by extension, tobramycin) 2
• Use tobramycin intermittently with different antibiotic classes between courses to prevent resistance development 2
• Do not use chronically without medical supervision, as this promotes resistant organism growth 5

Special Populations

• For children under 5 years with systemic infections requiring aminoglycosides, use 2.5 mg/kg every 8 hours systemically 5
• Discontinue contact lens wear during the entire treatment period for contact lens-related infections 5

When to Refer to Ophthalmology

• Refer immediately for: visual loss, moderate-to-severe pain, severe purulent discharge, corneal involvement, conjunctival scarring, lack of response after 3-4 days of appropriate therapy, or recurrent episodes 2
• Hospitalization is mandatory for neonatal conjunctivitis and may be necessary for severe gonococcal conjunctivitis 2