Proposal of anti-tuberculosis regimens based on susceptibility to isoniazid and rifampicin

Objective: To elaborate optimal anti-tuberculosis regimens following drug susceptibility testing (DST) to isoniazid (H) and rifampicin (R). Design: 12 311 M. tuberculosis strains (National Health Institute of Peru 2007-2009) were classified in four groups according H and R resistance. In each group the sensitivity to ethambutol (E), pirazinamide (Z), streptomycin (S), kanamycin (Km), capreomycin (Cm), ciprofloxacin (Cfx), ethionamide (Eto), cicloserine (Cs) and p-amino salicilic acid (PAS) was determined. Based on resistance profiles, domestic costs, and following WHO guidelines, we elaborated and selected optimal putative regimens for each group. The potential efficacy (PE) variable was defined as the proportion of strains sensitive to at least three or four drugs for each regimen evaluated. Results: Selected regimes with the lowest cost, and highest PE of containing 3 and 4 effective drugs for TB sensitive to H and R were: HRZ (99,5%) and HREZ (99,1%), respectively; RZECfx (PE=98,9%) and RZECfxKm (PE=97,7%) for TB resistant to H; HZECfx (96,8%) and HZECfxKm (95,4%) for TB resistant to R; and EZCfxKmEtoCs (82.9%) for MDR-TB. Conclusion: Based on resistance to H and R it was possible to select anti-tuberculosis regimens with high probability of success. This proposal is a feasible alternative to tackle tuberculosis in Peru where the access to rapid DST to H and R is improving progressively.