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- Litjens, Carlijn H. C., et al.
(author)
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Protein binding of rifampicin is not saturated when using high-dose rifampicin
- 2019
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In: Journal of Antimicrobial Chemotherapy. - : OXFORD UNIV PRESS. - 0305-7453 .- 1460-2091. ; 74:4, s. 986-990
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Journal article (peer-reviewed)abstract
- Background Higher doses of rifampicin are being investigated as a means to optimize response to this pivotal TB drug. It is unknown whether high-dose rifampicin results in saturation of plasma protein binding and a relative increase in protein-unbound (active) drug concentrations. Objectives To assess the free fraction of rifampicin based on an in vitro experiment and data from a clinical trial on high-dose rifampicin. Methods Protein-unbound rifampicin concentrations were measured in human serum spiked with increasing total concentrations (up to 64mg/L) of rifampicin and in samples obtained by intensive pharmacokinetic sampling of patients who used standard (10mg/kg daily) or high-dose (35mg/kg) rifampicin up to steady-state. The performance of total AUC(0-24) to predict unbound AUC(0-24) was evaluated. Results The in vitro free fraction of rifampicin remained unaltered (approximate to 9%) up to 21mg/L and increased up to 13% at 41mg/L and 17% at 64mg/L rifampicin. The highest (peak) concentration in vivo was 39.1mg/L (high-dose group). The arithmetic mean percentage unbound to total AUC(0-24)in vivo was 13.3% (range=8.1%-24.9%) and 11.1% (range=8.6%-13.6%) for the standard group and the high-dose group, respectively (P=0.214). Prediction of unbound AUC(0-24) based on total AUC(0-24) resulted in a bias of -0.05% and an imprecision of 13.2%. Conclusions Plasma protein binding of rifampicin can become saturated, but exposures after high-dose rifampicin are not high enough to increase the free fraction in TB patients with normal albumin values. Unbound rifampicin exposures can be predicted from total exposures, even in the higher dose range.
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| 2. |
- Svensson, Elin M., 1985-, et al.
(author)
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The Potential for Treatment Shortening With Higher Rifampicin Doses : Relating Drug Exposure to Treatment Response in Patients With Pulmonary Tuberculosis
- 2018
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In: Clinical Infectious Diseases. - : OXFORD UNIV PRESS INC. - 1058-4838 .- 1537-6591. ; 67:1, s. 34-41
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Journal article (peer-reviewed)abstract
- Background. Tuberculosis remains a huge public health problem and the prolonged treatment duration obstructs effective tuberculosis control. Higher rifampicin doses have been associated with better bactericidal activity, but optimal dosing is uncertain. This analysis aimed to characterize the relationship between rifampicin plasma exposure and treatment response over 6 months in a recent study investigating the potential for treatment shortening with high-dose rifampicin. Methods. Data were analyzed from 336 patients with pulmonary tuberculosis (97 with pharmacokinetic data) treated with rifampicin doses of 10, 20, or 35 mg/kg. The response measure was time to stable sputum culture conversion (TSCC). We derived individual exposure metrics with a previously developed population pharmacokinetic model of rifampicin. TSCC was modeled using a parametric time-to-event approach, and a sequential exposure-response analysis was performed. Results. Higher rifampicin exposures increased the probability of early culture conversion. No maximal limit of the effect was detected within the observed range. The expected proportion of patients with stable culture conversion on liquid medium at week 8 was predicted to increase from 39% (95% confidence interval, 37%-41%) to 55% (49%-61%), with the rifampicin area under the curve increasing from 20 to 175 mg/L.h (representative for 10 and 35 mg/kg, respectively). Other predictors of TSCC were baseline bacterial load, proportion of culture results unavailable, and substitution of ethambutol for either moxifloxacin or SQ109. Conclusions. Increasing rifampicin exposure shortened TSCC, and the effect did not plateau, indicating that doses >35 mg/kg could be yet more effective. Optimizing rifampicin dosage while preventing toxicity is a clinical priority.
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