Increased bactericidal activity but dose-limiting intolerability at 50 mg·kg⁻¹ rifampicin

Background

Accumulating data have indicated that higher rifampicin doses are more effective and shorten tuberculosis treatment duration. This study evaluated the safety, tolerability, pharmacokinetics, and 7 and 14-day early bactericidal activity (EBA) of increasing doses of rifampicin. Here we report the results of the final cohorts of PanACEA HIGHRIF1, a dose-escalation study in treatment-naive adult smear-positive patients with tuberculosis. 

Methods

Patients received, in consecutive cohorts, 40 or 50 mg·kg⁻¹ rifampicin once daily in monotherapy (day 1–7), supplemented with standard dose isoniazid, pyrazinamide and ethambutol between day 8–14. 

Results

In the 40 mg·kg⁻¹ cohort (n=15), 13 patients experienced a total of 36 adverse events (AEs) during monotherapy, resulting in one treatment discontinuation. In the 50 mg·kg⁻¹ group (n=17), all patients experienced AEs during monotherapy, 93 in total; 11 patients withdrew or stopped study medication. AEs were mostly mild/moderate and tolerability- rather than safety-related, i.e. gastrointestinal disorders, pruritis, hyperbilirubinemia and jaundice. There was a more than proportional increase in the rifampicin geometric mean AUC_0–24h for 50 mg·kg⁻¹ compared to 40 mg·kg; 571 mg·L*h⁻¹ (range 320–995) versus 387 mg·L*h⁻¹ (201–847), while peak exposures saw proportional increases. Protein-unbound exposure after 50 mg·kg⁻¹ (11%, 8–17%) was comparable with lower rifampicin doses. Rifampicin exposures and bilirubin concentrations were correlated (day-3 Spearman's rho 0.670, p<0.001). EBA increased considerably with dose, with the highest seen after 50 mg·kg⁻¹; 14-day EBA −0.427 logCFU·mL⁻¹·day⁻¹ (95%CI −0.500, −0.355).

Conclusion

Although associated with an increased bactericidal effect, the 50 mg·kg⁻¹ dose was not well tolerated. Rifampicin at 40 mg·kg⁻¹ was well tolerated and therefore selected for evaluation in a phase IIC treatment shortening trial.