Early Bactericidal Activity of Different Isoniazid Doses for Drug Resistant TB (INHindsight): A Randomized Open-label Clinical Trial.Am J Respir Crit Care Med 2020AJ
High-dose isoniazid is recommended in short-course regimens for multidrug-resistant TB (MDR-TB). The optimal dose of isoniazid and its individual contribution to efficacy against TB strains with inhA or katG mutations are unknown.
Define the optimal dose of isoniazid for patients with isoniazid-resistant TB mediated by inhA mutations.
AIDS Clinical Trials Group A5312 is a Phase 2A, open-label trial in which individuals with smear-positive pulmonary TB with isoniazid resistance mediated by an inhA mutation were randomized to receive isoniazid 5, 10 or 15 mg/kg daily for 7 days (inhA group), and controls with drug-sensitive TB received standard dose (5 mg/kg/day). Overnight sputum cultures were collected daily. The 7-day early bactericidal activity of isoniazid was estimated as the average daily change in log10 colony forming units on solid media (EBACFU0-7) or as time to positivity in liquid media in hours (EBATTP0-7) using nonlinear mixed effects models.
MEASUREMENTS AND MAIN RESULTS
Fifty-nine participants, 88% with cavitary disease, 20% HIV-positive, 16 with isoniazid-sensitive and 41 with isoniazid mono-resistant or MDR TB, were enrolled at one site in South Africa. Mean EBACFU0-7 at doses of 5, 10 and 15 mg/kg in the inhA group was 0.07, 0.17 and 0.22 log10CFU/mL/day, respectively, and 0.16 log10CFU/mL/day in controls. EBATTP0-7 patterns were similar. There were no drug-related Grade >3 adverse events.
Isoniazid 10-15 mg/kg daily had similar activity against TB strains with inhA mutations as 5 mg/kg against drug-sensitive strains. The activity of high-dose isoniazid against strains with katG mutations will be explored next. Clinical trial registration available at www.clinicaltrials.gov, ID: NCT01936831.