Correlation between serum isoniazid concentration and therapeutic response in patients of pulmonary tuberculosis in Central India: A prospective observational study

•There is an increasing numbers of tuberculosis patients not responding to therapy.•Early identification of patients prone for developing therapeutic failure is important in determining therapeutic outcome.•Low isoniazid levels serves as risk factor for treatment failure, relapse of disease and acquired secondary resistance.•The determination of serum isoniazid level is made less difficult and economical with use of spectrophotometric technique.