A more simple, rapid and sensitive fluorimetric method for the determination of isoniazid and acetylisoniazid in serum. Application for acetylator phenotyping.

A simple, rapid and sensitive fluorimetric method for isoniazid determination in serum is described. The method is based on the reaction of isoniazid with 2-hydroxy-1-naphthaldehyde in acidic medium in the presence of excess of scandium. Within-run precision (CV) was 1.5%, 1.0% and 1.2% at mean isoniazid concentration in serum of 0.244, 1.94, and 25.9 mg/l respectively (n = 10); between-run precision (CV) was 3.0%, 2.6%, and 1.9% at mean isoniazid concentration of 0.265, 1.93, and 26.2 mg/l respectively (n = 10). The linearity of the method extended over the range of 0-300 mg isoniazid/l serum. The detection limit (defined as three times the SD of the mean blank) for the method is 0.008 mg/l of serum. Samples from 80 tuberculous patients treated with isoniazid were analysed by the proposed method (y) and by the modified spectrofluorimetric method of Miceli et al (x). Linear regression analysis of the results yielded the equation y = 0.98x + 0.05 (r = 0.986, Sxy = 0.22).