Determination of iron by the Ferrochem II: interference by tuberculostatics

Iron levels in samples from certain treated tuberculous patients are underestimated by the Ferrochem II analyser. Of the tuberculostatic drugs examined for a possible interference, isoniazid, ethambutol, rifampicin, pyrazinamide and Rifater (a mixture of rifampicin, isoniazid and pyrazinamide), only pyrazinamide and Rifater (due to its pyrazinamide content) were associated with iron levels differing significantly (p < 0.001) from those of controls, with means of -317.2 and -185.6 mumol l-1 for pyrazinamide and Rifater respectively as against 9.91 mumol l-1 for the controls. The negative interference (I) due to pyrazinamide was independent of iron level in the samples but dependent on pyrazinamide concentration in the same (P) (r = 0.9993), I = -0.4380P-0.4276.