Isoniazid

證據等級: L5

預測適應症: 2 個

Isoniazid: From Tuberculosis to Conjunctivitis

One-Sentence Summary

Isoniazid is a first-line antitubercular agent, most commonly used for treatment and prevention of tuberculosis (including latent TB infection). The TxGNN model predicts it may be effective for Conjunctivitis, but this prediction is supported by only 1 loosely related clinical trial and 20 publications, most of which describe tuberculous conjunctivitis (a TB disease manifestation) rather than a pharmacological effect of isoniazid on conjunctivitis generally — and at least one source suggests isoniazid can itself cause drug-induced conjunctivitis, an opposite-direction signal.

Note: The evidence pack’s original_indications field for this drug is empty (data gap); “Tuberculosis” is inferred from the clinical-trial context (isoniazid 5 mg/kg regimen for latent TB infection) included in this pack, not from a confirmed registry entry.

Quick Overview

Item	Content
Original Indication	Tuberculosis (inferred from trial context; not confirmed in registry data)
Predicted New Indication	Conjunctivitis
TxGNN Prediction Score	99.36%
Evidence Level	L4
Denmark Market Status	Not marketed
Number of Marketing Authorisations	0
Recommended Decision	Hold

Why is This Prediction Reasonable?

Detailed, registry-sourced mechanism of action data is not currently available for this candidate (data gap). Based on the mechanistic review included in this evidence pack, isoniazid inhibits mycolic acid synthesis in Mycobacterium tuberculosis — a narrow-spectrum antimycobacterial mechanism with no established anti-inflammatory or broad antimicrobial activity relevant to common (viral, bacterial, or allergic) conjunctivitis.

The only genuine mechanistic link identified in the literature is to tuberculous conjunctivitis — conjunctival involvement as a manifestation of active or latent TB infection, and its resolution as a downstream consequence of treating the underlying TB, not a direct pharmacological effect on conjunctival inflammation itself. Several older publications (e.g. PMID 14253168, PMID 5103251) describe isoniazid used prophylactically or topically in TB-endemic, TB-associated eye disease, which is a materially different clinical scenario from “conjunctivitis” as a general indication.

Importantly, one review in this evidence pack (PMID 1363080) lists conjunctivitis among the ocular side effects of systemic drugs, raising the possibility that the TxGNN association reflects an adverse-effect signal rather than a therapeutic one. This directional ambiguity — supportive evidence limited to TB-specific ocular disease, alongside a plausible adverse-effect explanation — is the primary reason this candidate is rated at a low evidence level despite the high TxGNN score.

Clinical Trial Evidence

Trial Number	Phase	Status	Enrollment	Key Findings
NCT04094012	Phase 3	Completed	490	Compared systemic drug reaction rates between 3HP (rifapentine + isoniazid) and 1HP regimens for latent TB infection. This is a safety-monitoring trial, not a conjunctivitis efficacy trial — relevance graded “C” (indirect) in this evidence pack.

Literature Evidence

PMID	Year	Type	Journal	Key Findings
14253168	1965	Prophylaxis study	Am Rev Respir Dis	Isoniazid prophylaxis evaluated for phlyctenular keratoconjunctivitis in a TB-endemic Alaskan population
5103251	1971	Case series	Annales d’oculistique	Describes local (topical) use of isoniazid in treatment of ocular tuberculosis
1363080	1992	Review	Optometry Clinics	Review of ocular side effects of systemic drugs; conjunctivitis listed as an adverse effect of several drug classes — a cautionary, not supportive, signal
14089390	1964	Case report	Archives of Ophthalmology	Primary tuberculosis of the conjunctiva
26692731	2015	Case report	Middle East Afr J Ophthalmol	Tuberculous conjunctivitis in an anophthalmic socket following miliary TB
17133069	2006	Case report	Cornea	Mycobacterium tuberculosis presenting as chronic red eye (conjunctival TB)
33607832	2021	Case report	Medicine	Pediatric sinonasal TB presenting with phlyctenular keratoconjunctivitis
10641112	1999	Case series	Oftalmologia	28 cases of tuberculous keratoconjunctivitis, mostly children with primary TB
25433746	2014	Case report	Can J Ophthalmol	Conjunctival phlyctenulosis as presenting sign of impending clinical TB
4233886	1968	Case report	Arch d’ophtalmologie	Tuberculosis of the bulbar conjunctiva

Denmark Market Information

Isoniazid is currently not marketed in Denmark, and no marketing authorisations are recorded in this evidence pack.

Safety Considerations

Please refer to the approved Summary of Product Characteristics (SmPC) for safety information. No drug interaction data were found in this evidence pack, and key warnings/contraindications are not currently recorded — this is flagged as a blocking data gap (see Conclusion).

Conclusion and Next Steps

Decision: Hold

Rationale: Evidence level is L4 — the only clinical trial is indirectly relevant (a TB-regimen safety trial, not a conjunctivitis efficacy study), and the supporting literature largely describes TB-related ocular disease rather than a pharmacological effect on conjunctivitis in general. One source raises the possibility that isoniazid causes rather than treats conjunctivitis, directly conflicting with the TxGNN prediction direction.

To proceed, the following is needed:

SmPC warnings/contraindications data (currently a blocking gap — required before any safety pre-assessment, per this evidence pack)
Confirmed mechanism of action documentation (currently a high-severity gap affecting mechanistic-relevance analysis)
A study or trial specifically designed to test isoniazid’s effect on non-tuberculous conjunctivitis, to resolve the directional ambiguity in current evidence
Clarification of whether the TxGNN association reflects a therapeutic signal or an adverse-effect signal
Disclaimer

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