Adequacy of the 10 mg/kg Daily Dose of Antituberculosis Drug Isoniazid in Infants under 6 Months of Age

In 2010, the WHO recommended an increase in the daily doses of first-line anti-tuberculosis medicines in children. We aim to characterize the pharmacokinetics of the once-daily isoniazid (INH) dose at 10 mg/kg of body weight in infants n = 1), heterozygous intermediate (n = 12), and homozygous slow (n = 7). INH median (IQR) Cmax and AUC0–24h values were 4.8 (3.7–6.7) mg/L and 23.5 (13.4–36.7) h*mg/L and the adult targets (>3 mg/L and 11.6–26.3 h*mg/L) were not reached in three and five cases, respectively. The age at assessment or acetylator status had no impact on Cmax values, but a larger INH AUC0–24h (p = 0.025) and trends towards a longer half-life (p = 0.055) and slower clearance (p = 0.070) were observed in homozygous slow acetylators. Treatment was well tolerated; mildly elevated alanine aminotransferase levels were observed in three cases. In our series of young infants receiving isoniazid, no major safety concerns were raised, and the target adult levels were reached in most patients.