What is the appropriate management of visual disturbances in a patient receiving intravenous gentamicin?

Management of Visual Disturbances with Intravenous Gentamicin

Gentamicin does not cause visual disturbances—you are likely dealing with either ethambutol toxicity if the patient is on concurrent anti-mycobacterial therapy, or an unrelated ocular condition that requires immediate ophthalmologic evaluation. 1

Critical Distinction: Gentamicin Toxicity Profile

Gentamicin causes ototoxicity and nephrotoxicity, NOT visual disturbances when given systemically (IV/IM). The key toxic effects are: 1, 2

• Vestibulotoxicity: Vertigo, ataxia, nystagmus, imbalance (most common) 1, 2, 3
• Auditory toxicity: Hearing loss, tinnitus 1
• Nephrotoxicity: Renal impairment, often concurrent with vestibulotoxicity 2

Visual toxicity from gentamicin occurs only with direct intraocular injection (intravitreal), causing catastrophic retinal ischemia, hemorrhages, and often permanent blindness—this is not relevant to IV administration. 4, 5, 6

Immediate Action Required

If a patient on IV gentamicin reports visual disturbances, immediately investigate alternative causes:

Most Likely Culprit: Ethambutol (if applicable)

Ethambutol causes optic neuritis and retrobulbar neuritis, presenting with: 1

• Blurred vision 1
• Decreased visual acuity 1
• Central scotomas 1
• Impaired red-green color discrimination 1
• Peripheral visual field defects 1

Risk is dose-dependent: Very rare at 15 mg/kg/day but increases to ~3% at 25 mg/kg/day, especially with prolonged therapy and renal impairment. 1 In NTM treatment, ocular toxicity occurred in 6% with daily therapy versus 0% with intermittent therapy. 1

Management Algorithm for Visual Symptoms

1. Stop ethambutol immediately if patient is receiving it 1
2. Urgent ophthalmologic consultation to assess visual acuity, color vision, and fundoscopic examination 1
3. Continue gentamicin unless there are signs of ototoxicity or nephrotoxicity 1, 7
4. Do not restart ethambutol until ophthalmologic clearance 1

Monitoring Recommendations for Gentamicin (Not Visual)

Since gentamicin doesn't cause visual problems, focus monitoring on its actual toxicities:

Mandatory Monitoring 1, 7

• Serum creatinine and renal function: Monitor throughout therapy 1, 7
• Serum gentamicin levels: Peak (3-4 μg/mL, never >12 μg/mL) and trough (<1 μg/mL, never >2 μg/mL) 7
• Audiometry: Baseline and intermittent testing during treatment 1
• Patient education: Instruct to report tinnitus, vertigo, or hearing loss immediately and stop gentamicin 1

Dose Adjustment Critical 7

Patients with renal impairment require dose reduction. With creatinine clearance <50 mL/min, extend dosing intervals and reduce doses. 7 Consultation with infectious disease or clinical pharmacy is strongly recommended for dose optimization. 7

Common Clinical Pitfall

The most common error is attributing visual symptoms to gentamicin when the patient is actually on concurrent ethambutol therapy for mycobacterial infection. 1 Always review the complete medication list, as multi-drug regimens for NTM or TB commonly include both agents. 1

If No Ethambutol Exposure

Investigate other causes of acute visual disturbance: 1

• Giant cell arteritis (if elderly with systemic symptoms) 1
• Cerebrovascular event 1
• Other medication effects 8
• Primary ophthalmologic conditions 1

Visual disturbances warrant immediate ophthalmologic evaluation regardless of cause, but gentamicin is not the culprit. 1