Eye Drops Containing Polymyxin B
Polymyxin B is available in several ophthalmic preparations, most commonly combined with trimethoprim as an antimicrobial eye drop for treating ocular infections. 1, 2
Available Formulations
- Polymyxin B is typically found in ophthalmic solutions combined with trimethoprim (Polytrim®) as a broad-spectrum antimicrobial for ocular infections 1, 2
- Polymyxin B is also available in combination with neomycin and gramicidin (Neosporin® ophthalmic solution) 3
- Some formulations combine polymyxin B with bacitracin as an ophthalmic ointment 4
- For high-risk patients with Boston keratoprosthesis, polymyxin B is used in combination with trimethoprim or with a fourth-generation fluoroquinolone for antimicrobial prophylaxis 4
Mechanism of Action
- Polymyxin B is a cyclic lipopeptide antibiotic that is bactericidal against a variety of gram-negative organisms, especially Pseudomonas aeruginosa 1, 2
- It increases bacterial cell membrane permeability by interacting with phospholipid components 1, 2
- When combined with trimethoprim, the preparation provides coverage against both gram-negative and gram-positive pathogens 1, 2
Antimicrobial Spectrum
- Polymyxin B is effective against: Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, Enterobacter aerogenes, and Haemophilus influenzae 1, 2
- When combined with trimethoprim, the spectrum extends to include Staphylococcus species, Streptococcus species, and other gram-positive organisms 1, 2
Clinical Efficacy
- Polymyxin B/trimethoprim ophthalmic solution has demonstrated effectiveness in treating bacterial conjunctivitis with 95% of infected eyes showing cure or improvement within 7 days 5
- In comparative studies, polymyxin B/trimethoprim has shown similar efficacy to chloramphenicol ophthalmic ointment in treating bacterial conjunctivitis 6, 7
- However, newer fluoroquinolones like moxifloxacin may provide faster resolution of bacterial conjunctivitis symptoms (81% resolution at 48 hours) compared to polymyxin B/trimethoprim (44% resolution at 48 hours) 8
Special Considerations
- For patients with Boston keratoprosthesis, polymyxin B combined with trimethoprim is recommended as lifelong antimicrobial prophylaxis to prevent endophthalmitis 4
- High-risk patients with autoimmune conditions and/or monocular vision may require dual coverage with vancomycin combined with polymyxin B/trimethoprim 4
- Allergic contact dermatitis can occur with polymyxin B sulfate, with a prevalence of contact sensitivity reported between 1-30% in patients with chronic otitis externa 4
- Patients with known anaphylactic reactions to polymyxin B should not receive these eye drops 4
Administration
- Typical dosing for bacterial conjunctivitis is 1 drop four times daily for 7 days 8, 5
- Absorption through intact skin and mucous membranes is insignificant, with minimal systemic exposure 1, 2
When selecting an ophthalmic antimicrobial, consider the likely pathogens, local resistance patterns, and patient-specific factors such as allergies and comorbidities.