Overview of tuberculosis TB Treatment & Ethambutol Ocular Toxicity

👁 Overview of TB Treatment & Ethambutol Ocular Toxicity

Modern tuberculosis (TB) treatment relies on multi-drug regimens,
usually over a 6-month period, using first-line anti-TB drugs:

DrugAbbreviationFunction

Isoniazid	H	Bactericidal
Rifampin	R	Bactericidal
Ethambutol	E	Resistance prevention
Pyrazinamide	Z	Rapid kill effect

✅ Standard protocol: 2 HREZ / 4 HR

• First 2 months: H, R, E, Z
• Next 4 months: H, R

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💊 Fixed-Dose Combinations (FDC)

To improve adherence, FDCs combine 2–4 drugs into single tablets.
Effectiveness is comparable to separate dosing.

NameIncluded drugsDuration

TUBIS	H+R+E+Z	2 months
TUBIS-TWO	H+R	4 months

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⚠ Ethambutol-Induced Optic Neuropathy (EON)

• Occurs in 1–5% of patients
• Up to 50% risk of irreversible vision loss, even after stopping medication

❓ Why does it occur?

• 📉 Overdose? → Most regimens stay under 20 mg/kg
• 📆 Duration? → Typically used only for 2 months

➡️ Toxicity occurs even within standard guidelines, suggesting individual susceptibility plays a major role

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✅ Summary

• Ethambutol is effective but carries a known risk of optic nerve damage
• Visual monitoring is essential during treatment
• Prompt eye evaluation is crucial if any visual symptoms arise
• Physicians should be aware of EON risk, even in standard dosing