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Isoniazid (INH)

Antitubercularprescriptionoral · inferred

First-line tuberculosis drug and cornerstone of the RIPE regimen (Rifampin+Isoniazid+Pyrazinamide+Ethambutol). Prodrug activated by mycobacterial KatG catalase-peroxidase; inhibits mycolic acid synthesis in the cell wall. NAT2 acetylation polymorphism produces fast (t1/2 1-4h) and slow (t1/2 3-6h) acetylator phenotypes. CYP2E1 inhibition (~40%) increases acetaminophen hepatotoxicity risk via NAPQI shunting. Hepatotoxicity from CYP2E1-generated hydrazine metabolites is additive with other RIPE drugs. Peripheral neuropathy from B6 (pyridoxine) depletion — always co-administer pyridoxine 25-50 mg/day.

Projected serum levels — 300 mg, once daily

Isoniazid (INH)
Isoniazid (INH) modeled serum levels, 300 mg once daily over 15 days Population-based pharmacokinetic estimate. Steady state reached after approximately 1 days. 0 50 100 150 200 Day 0 Day 4 Day 8 Day 11 Day 15 Time on a regular schedule ≈ steady state · day 1

Maintenance schedule: 300 mg once daily (oral).

Modeled steady state after ~1 days: peak ≈ 195 mg, trough ≈ 1.2 mg body load. Population-based estimate over 15 days for a 300 mg dose at a 70 kg reference body mass — the interactive app scales curves to your doses, timing, and body mass.

Key facts

Category
Antitubercular
Route modeled
Oral
Model confidence
inferred
Half-life
3 h
Common dose
300 mg
Suggested maximum
300 mg/day
Reference dose range
100–300 mg (single dose)
Suggested cadence
once daily
Validated against
300 mg oral — Cmax 4 mg/L at 1.5 h

Documented interactions

  • danger
    7-Hydroxymitragynine (7-OH) + Isoniazid (INH) CYP inhibition

    Isoniazid (INH) reversible_inhibitor of CYP3A4 predicted to change 7-Hydroxymitragynine (7-OH) AUC by ~2.20x

  • danger
    Alfuzosin (Uroxatral) + Isoniazid (INH) CYP inhibition

    Isoniazid (INH) reversible_inhibitor of CYP3A4 predicted to change Alfuzosin (Uroxatral) AUC by ~3.33x

  • danger
    Alprazolam (Xanax) + Isoniazid (INH) CYP inhibition

    Isoniazid (INH) reversible_inhibitor of CYP3A4 predicted to change Alprazolam (Xanax) AUC by ~3.33x

  • danger
    Amlodipine (Norvasc) + Isoniazid (INH) CYP inhibition

    Isoniazid (INH) reversible_inhibitor of CYP3A4 predicted to change Amlodipine (Norvasc) AUC by ~3.33x

  • danger
    Anastrozole (Arimidex) + Isoniazid (INH) CYP inhibition

    Isoniazid (INH) reversible_inhibitor of CYP3A4 predicted to change Anastrozole (Arimidex) AUC by ~2.68x

  • danger
    Astaxanthin + Isoniazid (INH) CYP inhibition

    Isoniazid (INH) reversible_inhibitor of CYP3A4 predicted to change Astaxanthin AUC by ~3.33x

Serum checks 224 modeled interaction pairings for isoniazid (inh) across your whole stack — absorption conflicts, enzyme inhibition, and nutrient depletion included.

Research behind this entry

  1. Three months of rifapentine and isoniazid for latent tuberculosis infection Sterling TR et al. · New England Journal of Medicine, 2011 DOI

    Landmark PREVENT TB trial establishing 12-dose once-weekly rifapentine+isoniazid (3HP) as non-inferior to 9 months of daily isoniazid for LTBI, with higher completion rates (82% vs 69%) and lower hepatotoxicity (0.4% vs…

  2. American Thoracic Society/CDC/IDSA: Treatment of Tuberculosis Blumberg HM et al. · American Journal of Respiratory and Critical Care Medicine, 2003 DOI

    Foundational ATS/CDC/IDSA guidelines establishing the standard 6-month RIPE regimen and 9-month INH monotherapy for LTBI, with detailed hepatotoxicity monitoring protocols emphasizing baseline and monthly LFTs for…

2 published studies referenced in the app, each with a plain-language summary.