The need for systematic therapeutic drug monitoring of isoniazid in tuberculosis: A real-world study.

OBJECTIVES: Isoniazid is a primary first-line antituberculosis agent, exhibiting concentration-dependent bactericidal effect while also posing a risk of hepatotoxicity. Therapeutic drug monitoring could optimize exposure but remains underused. This study aimed to assess isoniazid pharmacokinetic variability in real-world settings and the proportion of patients achieving therapeutic concentrations.

METHODS: We conducted a retrospective, single-centre study of adult tuberculosis patients receiving standard first-line therapy (isoniazid, rifampicin, pyrazinamide, ethambutol). Patients underwent fasted-state isoniazid monitoring via a 4-point limited-sampling protocol. We calculated AUCand acetylation status (rapid: half-life <2.2 h; slow: &#x2265;2.2 h). Expected exposure was defined by a Cof 3-6 mg/L, while target exposure was defined by an AUCabove 10.5 h&#xb7;mg/L for bactericidal efficacy and below 21.8 h&#xb7;mg/L to minimize the risk of hepatotoxicity.

RESULTS: Among 109 patients (66.1% male, median age 40.7 y, 69.8% pulmonary tuberculosis), AUCshowed high interindividual variability (range 3.4-62.8 h&#xb7;mg/L, coefficient of variation 59.4%), independent of weight-adjusted dosing (Pearson's r = -0.016, P = 0.875). Slow acetylators predominated (59%). With a median dose of 4.1 mg/kg, 24 patients (22%) had subtherapeutic AUC(<10.5 h&#xb7;mg/L), while 52 (47.7%) exceeded the hepatotoxicity risk threshold (>21.8 h&#xb7;mg/L). Nearly one-third had Cwithin the expected range but AUCabove the safety limit.

CONCLUSIONS: Real-world data reveal substantial isoniazid exposure variability, with frequent deviations from target AUC. These findings advocate for systematic therapeutic drug monitoring and individualized dosing, prioritizing AUCas a key monitoring parameter.