Brand name: Gentak
Drug class: Antibacterials
CAS number: 1405-41-0

Medically reviewed by Drugs.com on Oct 19, 2023. Written by ASHP.

Introduction

Antibacterial; aminoglycoside.^{101 102}

Uses for Gentamicin (EENT)

Bacterial Ophthalmic Infections

Topical treatment of superficial bacterial infections of the eye caused by susceptible bacteria, including Staphylococcus aureus, S. epidermidis, Streptococcus pyogenes, S. pneumoniae, Enterobacter aerogenes, Escherichia coli, Haemophilus influenzae, Klebsiella pneumoniae, Neisseria gonorrhoeae, Serratia marcescens, and Pseudomonas aeruginosa.^{101 102}

Mild, acute bacterial conjunctivitis often resolves spontaneously without anti-infective treatment.^{135 136 137 141} Although topical ophthalmic anti-infectives may shorten time to resolution and reduce severity and risk of complications,^{135 136 137 141} avoid indiscriminate use of topical anti-infectives.^{135 141} Treatment of acute bacterial conjunctivitis generally is empiric;^{135 136 141} use of a broad-spectrum topical ophthalmic antibacterial usually recommended.^{135 136 141} In vitro staining and/or cultures of conjunctival material may be indicated in management of recurrent, severe, or chronic purulent conjunctivitis or when acute conjunctivitis does not respond to initial empiric topical treatment.^{135 136 141}

Because bacterial keratitis may be associated with subsequent loss of vision as the result of corneal scarring or topographic irregularities and because untreated or severe bacterial keratitis may result in corneal perforation with potential for endophthalmitis and possible loss of the eye, optimal management involves rapid evaluation and diagnosis, timely initiation of treatment, and appropriate follow-up.¹³⁸ Treatment of community-acquired bacterial keratitis generally is empiric;¹³⁸ use of a broad-spectrum topical ophthalmic antibacterial usually recommended.¹³⁸ Subconjunctival anti-infectives may be necessary if scleral spread or perforation is imminent.¹³⁸ In vitro staining and/or cultures of corneal material indicated in management of keratitis involving corneal infiltrates that are central, large, and extend to the middle to deep stroma; when keratitis is chronic or unresponsive to a broad-spectrum topical anti-infective; or when atypical features suggest fungal, amebic, or mycobacterial infection.¹³⁸

Ocular Inflammation

Fixed-combination ophthalmic preparations containing gentamicin and a corticosteroid (i.e., prednisolone): Topical treatment of corticosteroid-responsive ocular conditions when a corticosteroid indicated and superficial bacterial ocular infection or risk of such infection exists.^{107 108}

Although manufacturers state that use of a fixed-combination ophthalmic preparation containing an anti-infective and a corticosteroid may be indicated in ocular inflammatory conditions when risk of superficial ocular infection is high or when potentially dangerous numbers of bacteria are expected to be present in the eye,^{107 108} experts state avoid use of such preparations in patients with bacterial conjunctivitis because of risk of potentiating the infection.¹³⁶

Consider that use of fixed-combination ophthalmic preparations containing an anti-infective and a corticosteroid may mask clinical signs of bacterial, fungal, or viral infections; prevent recognition of ineffectiveness of the anti-infective; and/or increase IOP.^{107 108} (See Use of Fixed combinations Containing Corticosteroids under Cautions.)

Related/similar drugs

ciprofloxacin ophthalmic, azithromycin ophthalmic, levofloxacin ophthalmic, erythromycin ophthalmic, gentamicin ophthalmic

Gentamicin (EENT) Dosage and Administration

Administration

Ophthalmic Administration

Apply gentamicin ophthalmic ointment or solution topically to the eye.^{101 102}

Apply fixed-combination ophthalmic ointment or suspension containing gentamicin and a corticosteroid (i.e., prednisolone) topically to the eye.^{107 108}

For topical ophthalmic use only;^{101 102 107 108} do not inject subconjunctivally or directly into anterior chamber of the eye.^{101 102 108}

Avoid contaminating container tip with material from eye, eyelid, or any other source.^{101 102 107 108}

Shake fixed-combination ophthalmic suspension well prior to use.¹⁰⁸

Dosage

Available as gentamicin sulfate alone^{101 102} or in fixed combination with prednisolone acetate.^{107 108} Dosage of gentamicin expressed in terms of the base;^{101 102 107 108} dosage of prednisolone acetate expressed in terms of the salt.^{107 108}

Pediatric Patients

Bacterial Ophthalmic Infections

Ophthalmic

Gentamicin 0.3% (ophthalmic ointment) in pediatric patients ≥1 month of age: Apply approximately 1.25-cm (½-inch) ribbon in affected eye(s) 2 or 3 times daily.¹⁰²

Gentamicin 0.3% (ophthalmic solution) in pediatric patients ≥1 month of age: Instill 1 or 2 drops into affected eye(s) every 4 hours.¹⁰¹ For severe infections, up to 2 drops may be instilled every hour.¹⁰¹

Usual duration of topical anti-infective treatment for bacterial conjunctivitis is 5–10 days;^{135 136 141} 5–7 days usually adequate for mild bacterial conjunctivitis.¹³⁵

Adults

Bacterial Ophthalmic Infections

Ophthalmic

Gentamicin 0.3% (ophthalmic ointment): Apply approximately 1.25-cm (½-inch) ribbon in affected eye(s) 2 or 3 times daily.¹⁰²

Gentamicin 0.3% (ophthalmic solution): Instill 1 or 2 drops into affected eye(s) every 4 hours.¹⁰¹ For severe infections, up to 2 drops may be instilled every hour.¹⁰¹

Usual duration of topical anti-infective treatment for bacterial conjunctivitis is 5–10 days;^{135 136 141} 5–7 days usually adequate for mild bacterial conjunctivitis.¹³⁵

Ocular Inflammation

Ophthalmic

Gentamicin 0.3% and prednisolone acetate 0.6% (ophthalmic ointment): Apply approximately 1.25-cm (½-inch) ribbon into conjunctival sac of affected eye(s) 1–3 times daily.¹⁰⁷

Gentamicin 0.3% and prednisolone acetate 1% (ophthalmic suspension): Instill 1 drop into conjunctival sac of affected eye(s) 2–4 times daily.¹⁰⁸ During initial 24–48 hours, 1 drop may be instilled every hour if necessary.¹⁰⁸

If no improvement after 2 days, reevaluate patient.^{107 108} Do not discontinue prematurely.^{107 108}

Cautions for Gentamicin (EENT)

Contraindications

• Gentamicin ophthalmic ointment or solution: Hypersensitivity to gentamicin or any ingredient in the formulation.^{101 102}

• Fixed-combination ophthalmic preparations containing gentamicin and a corticosteroid (i.e., prednisolone): Known or suspected hypersensitivity to gentamicin, prednisolone or other corticosteroids, or any ingredient in the formulation.^{107 108} Also, patients with viral diseases of the cornea and conjunctiva, including epithelial herpes simplex keratitis (dendritic keratitis), vaccinia, and varicella; with mycobacterial infections of the eye; or fungal diseases of ocular structures.^{107 108}

Warnings/Precautions

Sensitivity Reactions

Hypersensitivity

Allergic reactions reported.^{101 102}

If hypersensitivity occurs, immediately discontinue^{101 102} and initiate appropriate therapy.^{101 102}

Superinfection

Prolonged use may result in overgrowth of nonsusceptible organisms, including fungi.^{101 102}

Bacterial resistance to gentamicin may occur.^{101 102}

Bacterial and fungal corneal ulcers have developed.^{101 102}

Precautions Related to Ophthalmic Administration

Manufacturer cautions that ophthalmic ointments may delay corneal healing.¹⁰²

Use of Fixed Combinations Containing Corticosteroids

When ophthalmic preparations containing gentamicin in fixed combination with a corticosteroid (i.e., prednisolone) used, consider cautions, precautions, and contraindications associated with EENT corticosteroids.^{107 108}

Provide initial prescriptions for fixed-combination ophthalmic preparations containing a corticosteroid or renewal prescriptions (beyond 8 g of ophthalmic ointment or beyond 20 mL of ophthalmic solution) only after measuring IOP and examining patient with slit lamp microscopy and, when appropriate, fluorescein staining.^{107 108}

Prolonged use of fixed-combination ophthalmic preparations containing a corticosteroid may result in glaucoma, with optic nerve damage, defects in visual acuity and fields of vision, and posterior subcapsular cataract formation.^{107 108} If such preparation used for ≥10 days, routinely monitor IOP, even though this may be difficult in children and uncooperative patients.^{107 108} Use fixed combinations containing a corticosteroid with caution in patients with glaucoma; check IOP frequently in such patients.^{107 108}

Use of fixed-combination ophthalmic preparations containing a corticosteroid after cataract surgery may delay healing and increase incidence of bleb formation.^{107 108}

Corneal and scleral thinning reported with various ocular diseases and with long-term use of topical corticosteroids.^{107 108} Use of topical corticosteroids in patients with thin corneal and scleral tissue may result in perforation.^{107 108}

Prolonged use of fixed-combination ophthalmic preparations containing a corticosteroid may suppress host responses and increase risk of secondary ocular infections.^{107 108} Use in patients with acute purulent conditions of the eye may mask infection or enhance existing infection.^{107 108}

May prolong course and exacerbate severity of many viral infections of the eye (including herpes simplex).^{107 108} Use with great caution in patients with herpes simplex; frequent slit lamp microscopy recommended.^{107 108}

Consider possibility of fungal infections of the cornea after prolonged use of ophthalmic preparations containing a corticosteroid.^{107 108} Perform fungal cultures when appropriate.^{107 108}

Specific Populations

Pregnancy

No adequate and well-controlled studies using ophthalmic preparations containing gentamicin in pregnant women.¹⁰²

Use gentamicin ophthalmic preparations, including fixed-combination preparations containing gentamicin and a corticosteroid, during pregnancy only if potential benefits justify potential risks to fetus.^{101 102 107 108}

Lactation

Systemic gentamicin is distributed into milk.¹⁴⁰

Discontinue nursing or the drug, taking into account importance of the drug to the woman.^{107 108}

Pediatric Use

Gentamicin ophthalmic ointment or solution: Safety and efficacy not established in neonates.^{101 102}

Fixed-combination ophthalmic preparations containing gentamicin and a corticosteroid (i.e., prednisolone): Safety and efficacy not established in pediatric patients.^{107 108}

Geriatric Use

Fixed-combination ophthalmic preparations containing gentamicin and prednisolone: No overall differences in safety or efficacy relative to younger adults.^{107 108}

Common Adverse Effects

Ocular burning and irritation, nonspecific conjunctivitis, conjunctival epithelial defects, conjunctival hyperemia.^{101 102}

Gentamicin (EENT) Pharmacokinetics

Absorption

Extent

Studies in rabbits suggest that gentamicin is absorbed into aqueous humor following topical application of the ophthalmic ointment or solution to the eye; also detected in vitreous humor.^a Absorption greatest when cornea is abraded.^a

Distribution

Extent

Systemic gentamicin crosses the placenta and is distributed into breast milk.¹⁴⁰

Stability

Storage

Ophthalmic

Ointment

Gentamicin 0.3%: 2–30°C.¹⁰²

Gentamicin 0.3% and prednisolone acetate 0.6%: 15–25°C.¹⁰⁷

Solution

Gentamicin 0.3%: 20–25°C; avoid excessive heat.¹⁰¹

Suspension

Gentamicin 0.3% and prednisolone acetate 1%: 15–25°C.¹⁰⁸ Do not freeze; protect from excessive heat (≥40°C).¹⁰⁸

Actions and Spectrum

• Aminoglycoside antibiotic obtained from cultures of Micromonospora purpurea.^{101 102}

• Usually bactericidal.^a

• Mechanism of action not fully elucidated; appears to inhibit protein synthesis in susceptible bacteria by irreversibly binding to 30S ribosomal subunits.^a

• Spectrum of activity of gentamicin includes many aerobic gram-negative and some aerobic gram-positive bacteria.^a Inactive against fungi, viruses, and most anaerobic bacteria.^a

• Gram-positive bacteria: Active in vitro against Staphylococcus aureus, S. epidermidis, Streptococcus pneumoniae, and S. pyogenes.^{101 102}

• Gram-negative bacteria: Active in vitro against Haemophilus influenzae, Enterobacter aerogenes, Escherichia coli, Klebsiella pneumoniae, Neisseria gonorrhoeae, Serratia marcescens, and Pseudomonas aeruginosa.^{101 102}

• Natural and acquired resistance to gentamicin demonstrated in both gram-negative and gram-positive bacteria.^a

• Partial cross-resistance occurs between gentamicin and other aminoglycosides.^a

Advice to Patients

• Advise patients to avoid contaminating container tip with material from eye, eyelid, or any other source.^{101 102} Keep container tightly closed when not in use; do not share with others.^{107 108}

• Advise patients to immediately discontinue gentamicin ophthalmic preparation and contact a clinician if irritation or hypersensitivity occurs.^{101 102} Also discontinue and contact a clinician if there is an increase in purulent discharge or aggravation of inflammation or pain.^{101 102}

• Advise patients using fixed-combination ophthalmic preparation containing a corticosteroid to discontinue the drug and contact a clinician if inflammation or pain persists for >48 hours or becomes aggravated.^{107 108}

• Importance of informing clinicians of existing or contemplated concomitant therapy, including prescription and OTC drugs, as well as any concomitant illnesses.^{101 102 107 108}

• Importance of women informing clinicians if they are or plan to become pregnant or plan to breast-feed.^{101 102 107 108}

• Importance of informing patients of other important precautionary information.^{101 102 107 108} (See Cautions.)

Additional Information

The American Society of Health-System Pharmacists, Inc. represents that the information provided in the accompanying monograph was formulated with a reasonable standard of care, and in conformity with professional standards in the field. Readers are advised that decisions regarding use of drugs are complex medical decisions requiring the independent, informed decision of an appropriate health care professional, and that the information contained in the monograph is provided for informational purposes only. The manufacturer’s labeling should be consulted for more detailed information. The American Society of Health-System Pharmacists, Inc. does not endorse or recommend the use of any drug. The information contained in the monograph is not a substitute for medical care.

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