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

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 mu g/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. Copyright (C) 2010 S. Karger AG, Basel