Abstract
Therapeutic drug monitoring may improve multidrug-resistant tuberculosis (MDR-TB) treatment outcomes. Levofloxacin demonstrates significant individual pharmacokinetic variability. Thus, we sought to develop and validate a high-performance liquid chromatography (HPLC) method with ultraviolet (UV) detection for levofloxacin in patients on MDR-TB treatment. The HPLC-UV method is based on a solid phase extraction (SPE) and a direct injection into the HPLC system. The limit of quantification was 0.25 μg/mL, and the assay was linear over the concentration range of 0.25—15 μg/mL (y = 0.5668x—0.0603, R2 = 0.9992) for the determination of levofloxacin in plasma. The HPLC-UV methodology achieved excellent accuracy and reproducibility along a clinically meaningful range. The intra-assay RSD% of low, medium, and high quality control samples (QC) were 1.93, 2.44, and 1.90, respectively, while the inter-assay RSD% were 3.74, 5.65, and 3.30, respectively. The mean recovery was 96.84%. This method was then utilized to measure levofloxacin concentrations from patients’ plasma samples from a retrospective cohort of consecutive enrolled subjects treated for MDR-TB at the national TB hospital in Tanzania during 5/3/2013–8/31/2015. Plasma was collected at 2 hours after levofloxacin administration, the time of estimated peak concentration (eCmax) treatment. Forty-one MDR-TB patients had plasma available and 39 had traceable programmatic outcomes. Only 13 (32%) patients had any plasma concentration that reached the lower range of the expected literature derived Cmax with the median eCmax being 5.86 (3.33–9.08 μg/ml). Using Classification and Regression Tree analysis, an eCmax ≥7.55 μg/mL was identified as the threshold which best predicted cure. Analyzing this CART derived threshold on treatment outcome, the time to sputum culture conversion was 38.3 ± 22.7 days vs. 47.8 ± 26.5 days (p = 0.27) and a greater proportion were cured, in 10 out of 15 (66.7%) vs. 6 out of 18 (33.3%) (p = 0.06) respectively. Furthermore, one patient with an eCmax/minimum inhibitory concentration (MIC) of only 1.13 acquired extensively drug resistant (XDR)-TB while undergoing treatment. The individual variability of levofloxacin concentrations in MDR-TB patients from Tanzania supports further study of the application of onsite therapeutic drug monitoring and MIC testing.
Highlights
Multidrug-resistant tuberculosis (MDR-TB), defined as resistance to both isoniazid and rifampin, has inferior treatment outcomes when compared to drug-susceptible TB in part because second-line medications have lower potency, higher side effect profiles and require longer durations of treatment [1,2]
We have previously shown among patients being treated with a standardized MDR-TB regimen in Tanzania that plasma drug activity as measured by an in vitro assay was driven by the concentrations relative to the minimum inhibitory concentrations (MICs) of kanamycin and levofloxacin [4,5]
These findings suggested that routine measurement of drug concentrations, termed therapeutic drug monitoring (TDM), could be of programmatic benefit
Summary
Multidrug-resistant tuberculosis (MDR-TB), defined as resistance to both isoniazid and rifampin, has inferior treatment outcomes when compared to drug-susceptible TB in part because second-line medications have lower potency, higher side effect profiles and require longer durations of treatment [1,2]. We have previously shown among patients being treated with a standardized MDR-TB regimen in Tanzania that plasma drug activity as measured by an in vitro assay was driven by the concentrations relative to the minimum inhibitory concentrations (MICs) of kanamycin and levofloxacin [4,5]. The in vitro assay does not quantify specific drug concentrations that would be necessary for dose adjustment. These findings suggested that routine measurement of drug concentrations, termed therapeutic drug monitoring (TDM), could be of programmatic benefit
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