What is Isoniazid?
Isoniazid (INH) is a first-line antibiotic medication used for the prevention and treatment of tuberculosis (TB). While effective against Mycobacterium tuberculosis, isoniazid is associated with potential side effects, including hepatotoxicity and peripheral neuropathy. Optic neuritis is another, less common, neurological adverse effect.
The Link Between Isoniazid and Optic Neuritis
Yes, isoniazid can cause optic neuritis, which is inflammation of the optic nerve. While less common than peripheral neuropathy, a connection has been established through case reports and studies. This form of toxic neuropathy is linked to the drug's effects on the body.
The Mechanism: Pyridoxine Deficiency
The primary cause of isoniazid-induced optic neuritis is the depletion of pyridoxine (vitamin B6). Isoniazid interferes with pyridoxine metabolism, and since vitamin B6 is vital for nervous system function, its deficiency can damage the optic nerve. Pyridoxine supplementation is a standard part of isoniazid therapy, especially for those at higher risk.
Signs and Symptoms
Symptoms often resemble other forms of toxic optic neuropathy and are typically symmetrical, affecting both eyes. These include decreased visual acuity, color vision deficits (particularly red-green), central or cecocentral scotoma (a blind spot), and eye pain that can occur with eye movement.
Risk Factors for Isoniazid Optic Neuritis
Factors that increase the risk include higher dosage and longer duration of treatment, nutritional deficiencies, comorbid conditions like diabetes, HIV, or kidney disease, alcoholism, and slow acetylator status.
Diagnosis, Management, and Prevention
Diagnosis involves an ophthalmologic exam and review of medication history. Report any visual changes to a healthcare provider immediately.
Management includes stopping isoniazid in severe cases, high doses of pyridoxine (50–100 mg daily), and ophthalmologic monitoring. Prevention involves prophylactic pyridoxine (25–50 mg daily) alongside isoniazid, particularly for those with risk factors.
Isoniazid vs. Ethambutol: A Comparison of Ocular Toxicity
Both isoniazid and ethambutol can cause optic neuropathy, but their mechanisms differ. Ethambutol is more commonly associated with optic neuropathy, while isoniazid's ocular toxicity is less frequent. Isoniazid-induced optic neuropathy is linked to pyridoxine deficiency, whereas ethambutol's mechanism may involve direct toxicity. Risk factors, symptom presentation, and prevention strategies also differ between the two medications. For a detailed comparison, refer to the table provided in {Link: LWW https://journals.lww.com/njpt/fulltext/2024/02010/antitubercular_treatment_induced_chronic.14.aspx}.
Prognosis and Long-Term Outcomes
Prognosis is generally good with early diagnosis and prompt discontinuation of isoniazid. Vision can often improve over weeks to months. However, delays can lead to permanent vision loss if optic atrophy occurs. Early detection is vital for the best possible outcome.
Conclusion
Isoniazid, an effective antitubercular drug, can rarely cause optic neuritis due to vitamin B6 interference. This risk is higher with certain factors like malnutrition or high doses. Visual changes require immediate medical attention. Routine pyridoxine supplementation is a key preventative measure. While vision recovery is often possible with timely action, permanent damage can occur. Patient education and monitoring are crucial for safe isoniazid use.
For further information on isoniazid, consult resources like the {Link: MedlinePlus drug information page https://medlineplus.gov/druginfo/meds/a682401.html}.
