Isoniazid

證據等級: L5

預測適應症: 10 個

Isoniazid: From Tuberculosis to Conjunctivitis

One-Sentence Summary

Isoniazid (INH) is a cornerstone first-line antituberculosis drug, widely used for both active tuberculosis treatment and latent tuberculosis infection (LTBI) prophylaxis across the globe. The TxGNN model predicts it may be effective for Conjunctivitis, with 1 clinical trial and 20 publications currently identified in support of this direction — though the preponderance of evidence pertains specifically to the tuberculosis-caused subtype of conjunctivitis, not general conjunctivitis. Given this narrow mechanistic scope and the absence of Singapore regulatory registration, the current evidence supports a Hold decision.

Quick Overview

Item	Content
Original Indication	Tuberculosis (active disease treatment and latent infection prophylaxis)
Predicted New Indication	Conjunctivitis
TxGNN Prediction Score	99.36%
Evidence Level	L4
Singapore Market Status	✗ Not marketed
Number of Registrations	0
Recommended Decision	Hold

Why is This Prediction Reasonable?

Currently, detailed mechanism of action data is not available from the regulatory data on file. Based on known pharmacological information, Isoniazid is a prodrug that is activated by the mycobacterial catalase-peroxidase enzyme (KatG). Once activated, it inhibits the InhA and KasA enzymes responsible for mycolic acid biosynthesis — a structural lipid unique to mycobacterial cell walls. This mechanism makes INH highly selective against Mycobacterium tuberculosis and closely related mycobacterial species, explaining why it has remained the backbone of anti-TB therapy for over seven decades.

The connection between INH and conjunctivitis is mechanistically coherent but anatomically narrow: it operates through tuberculous conjunctivitis, a rare but well-documented form of ocular tuberculosis in which M. tuberculosis directly infects conjunctival tissue. In such cases, INH — as the centerpiece of standard anti-TB regimens — would logically confer therapeutic benefit. Historical clinical series from the 1950s–1970s documented direct use of INH in ocular tuberculosis, and modern case reports continue to identify phlyctenular keratoconjunctivitis as a hypersensitivity manifestation of primary TB infection that responds to anti-TB therapy including INH. A 1965 Alaskan cohort study (PMID 14253168) specifically evaluated INH prophylaxis in Eskimo populations with high rates of this TB-associated conjunctivitis, providing the most direct human evidence in this niche indication.

The critical limitation is that general conjunctivitis — most commonly caused by adenoviruses, bacteria such as Haemophilus influenzae or Streptococcus pneumoniae, or allergic mechanisms — lies entirely outside INH's antimicrobial spectrum. The TxGNN model appears to have captured the TB–conjunctivitis disease overlap, which is mechanistically valid but represents an exceedingly rare and highly specific subtype. The high prediction score (99.36%) therefore likely reflects knowledge graph connectivity between tuberculosis and eye disease rather than a genuine broad repurposing opportunity.

Clinical Trial Evidence

Trial Number	Phase	Status	Enrollment	Key Findings
NCT04094012	Phase 3	Completed	490	Pragmatic RCT comparing systemic drug reactions under 3HP vs 1HP regimens for LTBI treatment in Taiwan. Research objective is regimen tolerability, not conjunctivitis as a treatment target. Relevance to conjunctivitis indication is indirect at best (Grade C).

Literature Evidence

PMID	Year	Type	Journal	Key Findings
14253168	1965	Cohort Study	Am Rev Respir Dis	Most directly relevant. INH prophylaxis for phlyctenular keratoconjunctivitis in Alaskan Eskimos with primary tuberculosis — direct human evidence of INH reducing TB-associated conjunctivitis incidence
5103251	1971	Clinical Series	Ann d'Oculistique	Local treatment of ocular tuberculosis with isoniazid — earliest direct application of INH in conjunctival and other ocular TB manifestations
33607832	2021	Case Report	Medicine	Pediatric phlyctenular keratoconjunctivitis secondary to primary sinonasal tuberculosis; resolved with INH-containing anti-TB regimen
17133069	2006	Case Report	Cornea	M. tuberculosis presenting as chronic red eye; histopathologically confirmed tuberculous conjunctivitis treated with INH-based therapy
26692731	2015	Case Report	Middle East Afr J Ophthalmol	Tuberculous conjunctivitis in an anophthalmic socket in a 27-year-old; successfully treated with standard anti-TB regimen
10641112	1999	Case Series	Oftalmologia	28 cases of tuberculous keratoconjunctivitis (13 in children with primary TB); all had positive tuberculin skin test and responded to anti-TB treatment
25433746	2014	Case Report	Can J Ophthalmol	Conjunctival phlyctenulosis as the presenting sign of impending clinical tuberculosis — re-emphasises the sentinel role of ocular TB findings
14089390	1964	Case Report	Arch Ophthalmol	Primary tuberculosis of the conjunctiva — among the earliest documentation of conjunctival TB as a distinct clinical entity
32674602	2020	Case Report	Clin Pediatrics	Unexpected cause of conjunctivitis in an adolescent — illustrates how atypical/mycobacterial etiologies can mimic common conjunctivitis
1363080	1992	Review	Optom Clin	Systemic drugs and ocular side effects; contextualises the drug–eye relationship including conjunctivitis associations with multiple agents

Singapore Market Information

Isoniazid currently has no registered products in Singapore. No license records or approved indication text are available for this drug in the Singapore Health Sciences Authority (HSA) database.

Safety Considerations

Please refer to the package insert for safety information.

Conclusion and Next Steps

Decision: Hold

Rationale: The TxGNN prediction captures a mechanistically coherent but extremely narrow indication — INH targets M. tuberculosis, so it is active against tuberculous conjunctivitis (a rare disease subtype) but has no biological plausibility for the vastly more common viral, bacterial, or allergic forms of conjunctivitis. All retrieved evidence is at the case report or historical cohort level (L4), no Singapore regulatory presence exists, and the drug already provides this effect as part of standard anti-TB therapy without requiring a formal new indication label.

To proceed, the following is needed:

Indication scoping: Clearly define whether the repurposing target is tuberculous conjunctivitis specifically or general conjunctivitis; the former has biological rationale, the latter does not
Mechanism of action data: Complete MOA profile from DrugBank (DrugBank ID: DB00951) to confirm or refute broader immunomodulatory activity that could explain a wider conjunctivitis effect
Singapore regulatory safety data: Obtain TFDA or equivalent package insert to extract contraindications and key warnings before any safety assessment can proceed (currently Blocking data gap)
Unmet need assessment: Epidemiological data on tuberculous conjunctivitis incidence in Singapore to evaluate whether a distinct repurposing label adds value beyond existing anti-TB prescribing practices
Expert ophthalmology input: Consult with infectious disease ophthalmologists to assess whether an INH-specific ocular TB indication would change clinical management compared to standard TB treatment
Disclaimer

This content is for research purposes only and does not constitute medical advice. Clinical validation is required before any clinical application.