Isoniazid Blood Levels in Patients with Pulmonary Tuberculosis at a Tuberculosis Referral Center

Abstract

BACKGROUND: Serum concentrations of isoniazid (INH) were evaluated in Iranian patients admitted to the Tuberculosis Ward of Masih Daneshvari Hospital, Tehran, Iran. Factors correlated to plasma INH levels were determined. METHODS: Blood samples were obtained 2 h after ingestion of 5 mg/kg INH in 82 patients (1 sample/patient) on days 3-15 of treatment. The following variables were investigated: INH plasma level, duration of therapy, age, sex, weight, dose of INH administered and smoking status. RESULTS: The average (±SD) age and weight of patients were 60.68 ± 18.53 years and 74.96 ± 7.15 kg, respectively. INH concentrations were low in 14.63% and high in 23.17% of the patients (INH reference range: 3-5 μg/ml). Plasma INH was statistically correlated with duration of INH administration (Kendall's rank correlation, r = 0.66, p < 0.001) but not with other variables. CONCLUSION: Based on the result of this study, plasma INH concentrations were not within the therapeutic range for 37.80% of the patients on conventional therapy. Therefore therapeutic drug monitoring may be needed to optimize INH dosage, especially in patients with inadequate clinical response or toxicity to INH.