Gentamicin is used topically in the treatment of superficial infections of the eye caused by susceptible bacteria.
Although most cases of mild bacterial conjunctivitis improve without anti-infective therapy, topical application of anti-infectives may shorten the infectious process. In addition, topical application of anti-infectives may reduce recurrence rate and morbidity associated with bacterial conjunctivitis.
Gentamicin also is used topically in conjunction with topical corticosteroids in some cases of bacterial ocular infections. Concomitant therapy with a corticosteroid may be used for steroid-responsive ocular inflammatory conditions for which a corticosteroid is indicated and where a superficial ocular bacterial infection or risk of ocular bacterial infection exists. However, the benefit of concomitant therapy must be weighed against reduced resistance to bacterial, fungal, or viral infections and suppression of signs and symptoms of infection or hypersensitivity. (See Cautions: Precautions and Contraindications.)
For systemic uses of gentamicin, see the Aminoglycosides General Statement 8:12.02; for use in superficial infections of the skin, see 84:04.04.
Dosage and Administration
Gentamicin sulfate is applied topically to the eye in the form of a solution or ointment containing 0.3% gentamicin. Gentamicin sulfate ophthalmic solution is not for injection and should not be injected subconjunctivally or directly into the anterior chamber of the eye.
For the treatment of superficial infections of the eye caused by susceptible bacteria, 1 or 2 drops of gentamicin sulfate ophthalmic solution may be instilled into the infected eye every 4 hours. In severe infections, up to 2 drops every hour may be used. Alternatively, a small amount of the ointment (approximately 1.3-cm ribbon) may be placed into the conjunctival sac 2 or 3 times daily taking care to avoid contamination of the tip of the ointment tube.
Gentamicin appears to have a low order of toxicity when applied topically to the eye; however, sensitization to the drug may occasionally result from topical application. In addition, commercially available gentamicin preparations contain other ingredients such as parabens which may also cause allergic contact dermatitis. If irritation or hypersensitivity occurs during topical gentamicin therapy, gentamicin should be discontinued.
Transient irritation, burning, or a stinging sensation has occurred occasionally following topical application of gentamicin ophthalmic preparations. Rarely, increased redness and lacrimation have been reported.
Precautions and Contraindications
The use of gentamicin may result in overgrowth of nonsusceptible organisms including fungi. If superinfection occurs during gentamicin therapy, the drug should be discontinued and appropriate therapy instituted.
Topical corticosteroids, when used in combination with gentamicin, may mask the clinical signs of bacterial, fungal, or viral infections, or may suppress hypersensitivity reactions to the antibiotic or other ingredients in the formulations. The possibility of corticosteroid-induced adverse ocular effects, including increased intraocular pressure, glaucoma, delayed wound healing, and cataract formation, also must be considered. When gentamicin is used in fixed combination with a corticosteroid, other cautions, precautions, and contraindications associated with EENT corticosteroids also must be considered in addition to those associated with the anti-infective. (See Cautions, in the EENT Corticosteroids General Statement 52:08.08.) In addition, such fixed combinations are contraindicated following uncomplicated removal of a corneal foreign body.
Gentamicin sulfate ophthalmic preparations are contraindicated in patients who are hypersensitive to the drug or any ingredients in the formulations. Cross-allergenicity among the aminoglycosides has been demonstrated and the possibility that patients who become sensitized to topical gentamicin may also be sensitive to other topical and/or systemic aminoglycosides should be considered.
Studies in rabbits suggest that gentamicin is absorbed into the aqueous humor following topical application of the ophthalmic ointment or solution to the eye; no antibiotic was detected in the vitreous humor. Absorption of the drug is greatest when the cornea is abraded.