Isoniazid: an update on the multiple mechanisms for a singular action

Area of Science:

• Microbiology
• Pharmacology
• Medicinal Chemistry

Background:

• Isoniazid (INH) is a cornerstone drug for treating tuberculosis (TB), known for its high efficacy.
• Despite its long history and simple structure (C₆H₇N₃O), INH's exact mechanism of action against Mycobacterium tuberculosis remains incompletely understood.
• Existing resistance patterns and INH's specific potency are not fully explained by current models.

Purpose of the Study:

• To critically review and synthesize existing literature on isoniazid's diverse proposed mechanisms of action.
• To explore the molecular basis for isoniazid's effectiveness and resistance in Mycobacterium tuberculosis.
• To provide a comprehensive understanding of INH's action in light of current scientific knowledge.

Main Methods:

• Literature review and critical analysis of published studies on isoniazid's mechanism of action.
• Examination of biochemical pathways and molecular targets implicated in INH activity.
• Correlation of proposed mechanisms with observed isoniazid resistance profiles.

Main Results:

• The most accepted mechanism involves INH conversion to an active metabolite that inhibits InhA, an essential enzyme for M. tuberculosis survival.
• However, this consensual mechanism alone does not account for all observed resistance profiles or INH's unique efficacy.
• The high reactivity of INH suggests potential for multiple targets and co-existing pathways contributing to its action.

Conclusions:

• A single, unified mechanism may not fully explain isoniazid's complex action and resistance patterns.
• Further research into the molecular intricacies of INH's interaction with M. tuberculosis is necessary.
• Understanding these mechanisms is crucial for optimizing tuberculosis treatment and combating drug resistance.