The best antibiotic for an eye infection in adults depends on the type and severity of the infection. Topical antibiotics are generally recommended to deliver high levels of the drug directly to the site of infection, exceeding what is normally achieved in body tissues by oral or parenteral routes. According to the search results, some of the most commonly prescribed antibiotics for bacterial eye infections include:

• Azithromycin: This is a macrolide antibiotic that is effective in treating bacterial conjunctivitis caused by CDC coryneform group G bacteria, H influenzae, S aureus, S mitis group, and S pneumoniae. It is especially effective against pediatric conjunctivitis owing to its efficient dosage regimen requiring only 9 drops of medication over 7 days.

• Chloramphenicol: This is a bacteriostatic broad-spectrum antibiotic that is commonly prescribed as a first-line treatment for red eye. However, it lacks activity against P. aeruginosa, and primary healthcare providers should not prescribe it when microbial keratitis is suspected as this delays appropriate treatment, with the risk of the patient losing vision or the eye.

• Ciprofloxacin: This is a fluoroquinolone antibiotic that is effective in the treatment of bacterial corneal ulcers and bacterial conjunctivitis. However, many bacterial-resistant strains are also emerging in keratitis, and later-generation fluoroquinolones should be reserved for more severe cases of conjunctivitis.

• Tobramycin: This is an aminoglycoside antibiotic that is effective in treating bacterial conjunctivitis. It is available as Tobrex, Tobrasol, Tomycine, and Tobralcon.

It is important to note that the choice of antibiotic should be guided by the severity of the infection, and cultures may be needed to guide the choice of antibiotic for severe conjunctivitis marked by copious purulent discharge and eye inflammation. It is also important to follow the exact instructions by the doctor or ophthalmologist and not stop using the eye drops sooner than the prescribed length of therapy to help clear up the eye infection completely.