Isoniazid
| Evidence Level: L4 | Predicted Indications: 1 |
Table of Contents
Isoniazid: From Tuberculosis to Conjunctivitis
One-Sentence Summary
Isoniazid is a first-line antitubercular agent, established practice for tuberculosis. The TxGNN model predicts it may be relevant to Conjunctivitis, but supporting evidence is thin: 1 clinical trial (not directly testing this indication) and 20 historical publications, most describing tuberculosis-associated eye disease rather than a direct treatment trial for conjunctivitis.
Quick Overview
| Item | Content |
|---|---|
| Original Indication | Tuberculosis (established clinical use; no formal marketing-authorisation indication text on file in this dataset) |
| Predicted New Indication | Conjunctivitis |
| TxGNN Prediction Score | 99.36% |
| Evidence Level | L4 |
| UK Market Status | Not marketed |
| Number of Marketing Authorisations | 0 |
| Recommended Decision | Hold |
Why is This Prediction Reasonable?
Currently, detailed mechanism of action data is not available (flagged as a data gap). Based on established pharmacological knowledge, isoniazid is a prodrug activated by mycobacterial catalase-peroxidase (KatG), which inhibits mycolic acid synthesis in Mycobacterium tuberculosis; its efficacy in tuberculosis is well proven.
The link to conjunctivitis in the evidence base is not a direct antimicrobial or anti-inflammatory action on the eye itself. Instead, the literature consistently points to phlyctenular keratoconjunctivitis and other conjunctival manifestations that occur as a hypersensitivity reaction to tuberculoprotein, secondary to underlying (often latent or unrecognised) tuberculosis infection. In this context, isoniazid resolves the conjunctivitis indirectly, by treating the causative tuberculous infection rather than by a distinct ocular mechanism.
This distinction matters clinically: the prediction should be interpreted as “isoniazid may resolve conjunctivitis of tuberculous aetiology,” not “isoniazid is a general treatment for conjunctivitis.” The one included clinical trial (NCT04094012) does not test this indication at all — it compares isoniazid-containing regimens for latent TB infection safety/tolerability, and was likely surfaced because it involves isoniazid, not because it studies conjunctivitis outcomes.
Clinical Trial Evidence
| Trial Number | Phase | Status | Enrolment | Key Findings |
|---|---|---|---|---|
| NCT04094012 | Phase 3 | Completed | 490 | Compared systemic drug reaction rates between 3-month weekly (3HP) and 1-month daily (1HP) isoniazid + rifapentine regimens for latent tuberculosis infection. Addresses isoniazid safety/tolerability, not a conjunctivitis outcome. |
No trial in this evidence pack directly evaluates isoniazid for treatment of conjunctivitis.
Literature Evidence
| PMID | Year | Type | Journal | Key Findings |
|---|---|---|---|---|
| 14253168 | 1965 | Field/Prophylaxis study | Am Rev Respir Dis | Isoniazid prophylaxis studied in a population with phlyctenular keratoconjunctivitis linked to TB exposure (Alaska Eskimo cohort) |
| 5103251 | 1971 | Case series | Annales d’oculistique | Local (topical) use of isoniazid reported in treatment of ocular tuberculosis |
| 25433746 | 2014 | Review/Commentary | Can J Ophthalmol | Highlights conjunctival phlyctenulosis as a presenting sign of impending clinical tuberculosis |
| 10641112 | 1999 | Case series | Oftalmologia | 28 cases of tuberculous phlyctenular keratoconjunctivitis, mostly paediatric, linked to primary TB |
| 33607832 | 2021 | Case report | Medicine | Paediatric sinonasal TB presenting with phlyctenular keratoconjunctivitis |
| 17133069 | 2006 | Case report | Cornea | M. tuberculosis presenting as chronic red eye (conjunctival TB) |
| 26692731 | 2015 | Case report | Middle East Afr J Ophthalmol | Tuberculous conjunctivitis in an anophthalmic socket following prior miliary TB |
| 14089390 | 1964 | Case report | Arch Ophthalmol | Primary tuberculosis of the conjunctiva |
| 4233886 | 1968 | Case report | Arch Ophtalmol | Tuberculosis of the bulbar conjunctiva |
| 32674602 | 2020 | Case report | Clin Pediatr | Unusual paediatric conjunctivitis case with a tuberculous cause |
Note: study-type classification for these records was still “pending” in the source evidence pack; types above are inferred from titles/context and should be verified. Several additional retrieved records (e.g. BCG-induced polyarthritis reports, a Munchausen syndrome case, a rifampicin monograph) were excluded as not materially relevant to this indication.
UK Market Information
Isoniazid currently has no marketing authorisation on file in this jurisdiction (0 licences; market status: not marketed). No product-level licence, dosage form, or approved-indication text is available to report.
Safety Considerations
Please refer to the SmPC and BNF for safety information. Report suspected adverse reactions via the Yellow Card Scheme.
Note: a Blocking data gap exists for local SmPC/label warnings and contraindications, and drug interaction data returned no results — safety information cannot be independently verified from this evidence pack.
Conclusion and Next Steps
Decision: Hold
Rationale: A Blocking data gap on label warnings/contraindications means safety cannot be assessed at all, the mechanism-of-action record is missing, the drug is not currently marketed in this jurisdiction, and the clinical/literature evidence for “conjunctivitis” is essentially all historical case reports of TB-associated eye disease rather than trials of isoniazid for conjunctivitis itself.
To proceed, the following is needed:
- Official SmPC/PIL warnings and contraindications (resolve DG001, Blocking)
- Confirmed mechanism of action from DrugBank (resolve DG002)
- Clarification of the true target population — this signal appears specific to tuberculosis-associated phlyctenular keratoconjunctivitis, not conjunctivitis in general — before any indication framing is used
- A regulatory pathway assessment, given isoniazid holds no current marketing authorisation in this jurisdiction
Disclaimer
This content is for research purposes only and does not constitute medical advice. Clinical validation is required before any clinical application.