Quickly Fixes For the RRAD Concerns

In mice, while increased doses of rifampicin alone after prolonged treatment were able to achieve organ CFU count negativity and reduced RPF-dependent bacteria; only high-dose of rifampicin (50 mg/kg) was able to eradicate the persisters in lungs (Table ?Table33). Furthermore, we have shown here that in the Cornell model, high-dose rifampicin regimen eliminates all persisters, even the RPF dependent subpopulation (Table ?Table44). It has been found that in human tuberculosis prior to treatment, smear-positive sputa contained a considerable amount of RPF dependent persisters (Mukamolova et al., 2010). Furthermore, the numbers of RPF-dependent persisters was enhanced after standard chemotherapy compared with the plate counts positive populations (Mukamolova et al., 2010). It is not known whether the persisters we found in vitro and in vivo were the same as those in humans and if rifampicin treatment in mice necessarily predicts the situation with rifampicin in humans. We have recently highlighted (Coates et al., 2013) contradictory results with high-dosage rifamycin in mice and humans. Tuberculosis infections are different between mice and man, not least the absence of RRAD caseating granulomas in mice. Therefore, the interpretation of our data and the subsequent translation into human studies need to be undertaken with caution. It has been proposed recently (Mitchison, 2012) that peak drug concentrations are better indicators than AUC for predicting higher degrees of persister-eradication and lower relapse rates. This is based on TB patients (rapid or slow acetylators) treated with isoniazid in whom the magnitude of clinical response was related to peak concentration of the drug (Mitchison, 2012). Repeated peaks can kill low-level resistant mutants. The same may be true for rifampicin (Mitchison, 2012) because repeated peak concentrations of rifamycins kill low antibiotic-tolerant persisters (Hu et al., 2000; Mitchison, 2012). Our results show that the PK value at 10 mg/kg gave a Cmax in blood of 11 mg/L and an AUC0-24 h of 121 mg h/L which was very similar to those of previous studies in mice (Rosenthal et al., 2012; de Steenwinkel et al., 2013) and in humans (Doble et al., 1988; Sirgel et al., 2005). The PK values of rifampicin increased proportionally with increasing doses of rifampicin which was also in agreement with previous murine study (Rosenthal et al., 2012; de Steenwinkel et al., 2013). Although standard doses of rifampicin achieved a blood level of 11 mg/L, only 3.3% of free drug (de Steenwinkel et al., 2013) was able to diffuse to the lesion and inhibit bacterial growth as 97�C98% of rifampicin or rifapentine was bound to plasma protein (Mitchison, 1998; de Steenwinkel et al., 2013). This suggests that a standard dose of rifampicin is not high enough to kill persistent organisms which are present at the beginning of the treatment and formed during the antibiotic treatment.