Should I stop Ethambutol (Ethambutol) in a TB (Tuberculosis) patient who develops blurred vision after 10 days of HRZE (Isoniazid, Rifampicin, Pyrazinamide, and Ethambutol) treatment, and how to confirm Ethambutol-associated optic neuritis?

Management of Ethambutol-Associated Visual Changes in TB Treatment

You should immediately stop ethambutol in this TB patient who developed blurring of vision after 10 days of HRZE treatment, as this is likely ethambutol-associated optic neuritis requiring prompt discontinuation to prevent permanent vision loss. 1

Diagnosis of Ethambutol-Associated Optic Neuritis

To confirm ethambutol-associated optic neuritis, perform the following evaluations:

1. Visual acuity testing using Snellen chart (compare with baseline if available) 2
2. Color vision assessment with emphasis on red-green color discrimination 2, 3
3. Visual field testing to detect central scotomas and peripheral visual field defects 3
4. Ophthalmology referral for comprehensive evaluation 3

The diagnosis is primarily clinical and based on:

• Temporal relationship between ethambutol initiation and symptom onset (10 days in this case)
• Characteristic symptoms (blurred vision)
• Exclusion of other causes of visual disturbance

Management Algorithm

Immediate Steps:

1. Discontinue ethambutol immediately 2, 1

   • Do not wait for confirmatory tests when visual symptoms appear
   • The FDA label explicitly states: "Progressive decreases in visual acuity during therapy must be considered to be due to ETHAMBUTOL HCl" 1

2. Arrange urgent ophthalmological evaluation 3

   • To confirm diagnosis and assess severity
   • To rule out other causes of visual disturbance

3. Modify TB treatment regimen

   • Continue other drugs (HRZ - Isoniazid, Rifampicin, Pyrazinamide)
   • Consider adding a fluoroquinolone (e.g., levofloxacin or moxifloxacin) as replacement for ethambutol 3

Monitoring:

• Schedule frequent follow-up visits to monitor visual function
• Recovery of visual acuity generally occurs over weeks to months after drug discontinuation 1
• Some patients may not experience complete recovery, particularly if diagnosis is delayed 4

Important Considerations

Risk Factors for Ethambutol Toxicity:

• Higher doses (particularly >25 mg/kg/day) 3
• Renal impairment (ethambutol is primarily excreted by the kidneys) 4
• Older age 3
• Duration of treatment (though toxicity can occur early, as in this case)

Prognosis:

• Most cases of ethambutol-induced optic neuritis are reversible upon prompt discontinuation 5
• However, irreversible vision loss can occur, particularly with delayed recognition 1, 6
• Recovery typically occurs over weeks to months 1

Common Pitfalls to Avoid:

1. Delaying discontinuation of ethambutol while awaiting confirmatory tests
2. Failing to perform baseline visual testing before starting ethambutol (for future reference)
3. Reintroducing ethambutol after an episode of optic neuritis (high risk of recurrence)
4. Overlooking renal function which affects ethambutol clearance and toxicity risk

Prevention for Future Patients

• Perform baseline visual acuity and color vision testing before starting ethambutol 2, 3
• Educate patients to report visual changes immediately 2, 1
• Consider monthly visual monitoring for high-risk patients (those on >15 mg/kg/day) 1
• Adjust dosage in patients with renal impairment 3, 4

Remember that while ethambutol is an important component of TB treatment, preserving vision is critical for quality of life. Prompt recognition and management of ocular toxicity is essential to prevent permanent visual impairment.