What are the uses of Polymyxin (Polymyxin B) eye drops?

From the Guidelines

Polymyxin eye drops are not the preferred initial treatment for bacterial keratitis, and fluoroquinolones such as ciprofloxacin, ofloxacin, or levofloxacin are recommended instead. When considering the use of polymyxin eye drops, it's essential to weigh the potential benefits against the risks, particularly in the context of increasing resistance to fluoroquinolones 1. The most recent guidelines suggest that topical antibiotic eye drops, such as fluoroquinolones, are capable of achieving high tissue levels and are the preferred method of treatment in most cases of bacterial keratitis 1.

Some key points to consider when treating bacterial keratitis include:

• The use of ocular ointments is not recommended due to their lack of solubility and limited ability to penetrate the cornea 1
• Subconjunctival antibiotic injections may be helpful in cases where adherence is questionable or a delay in obtaining fortified antibiotics is anticipated 1
• Systemic therapy may be useful in cases of scleral or intraocular extension of infection or systemic infection such as N. gonorrhoeae 1
• Cycloplegic agents may be used to decrease synechiae formation and decrease pain from anterior segment inflammation associated with bacterial keratitis 1

It's also important to note that polymyxin has been shown to be effective in combination with other treatments, such as aerosolized polymyxin, in reducing mortality rate, clinical treatment failure, and increasing clearance of pathogens in cases of carbapenem-resistant gram-negative bacilli 1. However, this does not necessarily apply to the treatment of bacterial keratitis, and fluoroquinolones remain the preferred initial treatment 1.

In terms of administration, it's crucial to follow proper techniques to ensure the effective delivery of the medication and minimize potential side effects. This includes washing hands thoroughly, tilting the head back, pulling down the lower eyelid to create a pocket, and placing the drop in this pocket without touching the eye or eyelid with the dropper.

From the FDA Drug Label

INDICATIONS AND USAGE Polymyxin B Sulfate and Trimethoprim Ophthalmic Solution, USP is indicated in the treatment of surface ocular bacterial infections, including acute bacterial conjunctivitis, and blepharoconjunctivitis, caused by susceptible strains of the following microorganisms: Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pneumoniae, Streptococcus viridans, Haemophilus influenzae and Pseudomonas aeruginosa. CLINICAL PHARMACOLOGY Trimethoprim is a synthetic antibacterial drug active against a wide variety of aerobic gram-positive and gram-negative ophthalmic pathogens. Polymyxin B, a cyclic lipopeptide antibiotic, is bactericidal for a variety of gram-negative organisms, especially Pseudomonas aeruginosa The Polymixin eye drops are used to treat surface ocular bacterial infections, including:

• Acute bacterial conjunctivitis
• Blepharoconjunctivitis Caused by susceptible strains of microorganisms such as:
• Staphylococcus aureus
• Staphylococcus epidermidis
• Streptococcus pneumoniae
• Streptococcus viridans
• Haemophilus influenzae
• Pseudomonas aeruginosa 2 2

From the Research

Polymixin Eye Drops

• Polymixin eye drops are used to treat bacterial conjunctivitis, with studies showing their effectiveness in reducing signs and symptoms of the infection 3, 4.
• A study from 1988 compared the efficacy of trimethoprim-polymyxin B (TP) with gentamicin sulfate (GS) and sodium sulfacetamide (SS) in treating acute bacterial conjunctivitis, finding similar clinical responses among the three treatments 3.
• Another study from 1983 found that trimethoprim-polymyxin B was significantly better than chloramphenicol in reducing signs and symptoms of presumptive bacterial conjunctivitis 4.
• The use of polymixin eye drops is supported by systematic reviews, which have found that topical antibiotics, including polymixin, can decrease the duration of bacterial conjunctivitis and allow for earlier return to school or work 5, 6.

Mechanism of Action

• Polymixin works by disrupting the bacterial cell membrane, ultimately leading to the death of the bacterial cells 3.
• The combination of trimethoprim and polymyxin B has been shown to be effective against a range of bacterial species, including Haemophilus influenzae and Streptococcus pneumoniae 3.

Comparison with Other Treatments

• Polymixin eye drops have been compared with other topical antibiotics, such as gentamicin and chloramphenicol, with varying results 3, 4.
• A systematic review from 2001 found that topical antibiotics, including polymixin, were associated with significantly better rates of early clinical remission and microbiological remission compared to placebo 6.