The therapeutic range within which the 4-drug FDC (RHZE) recommended by WHO is effective and not toxic is illustrated in Figures 2-5 below. The charts demonstrate that, for the anti-TB drugs included in the FDC tablet, varying the dosage schedule according to body weight ensures that the dose remains within the therapeutic margin.
Figures 2-5: Dose distributions of the four FDC drugs
(rifampicin 150 mg, isoniazid 75 mg, pyrazinamide 400 mg, ethambutol 275 mg) recommended by WHO (by body weight cut-off points of 30-37 kg, 38-54 kg, 55-70 kg, 71 kg and above).
Figure 2: Rifampicin dosage
Figure 3: Isoniazid dosage
Note: The body weight range is adequately covered by all drugs in the 4-drug FDC formulation, i.e. the doses in mg per kg body weight do not breach the minimum or maximum cut-off points.
Figure 4: Pyrazinamide dosage
Figure 5: Ethambutol dosage