title: Determination of plasma concentrations of levofloxacin by high performance liquid chromatography for use at a multidrug-resistant tuberculosis hospital in Tanzania.
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.
authors.affiliation: Division of Infectious Diseases and International Health, University of Virginia, Charlottesville, United States of America.
authors.forename: Andrew
authors.initials: A
authors.lastname: Ebers
authors.affiliation: Division of Infectious Diseases and International Health, University of Virginia, Charlottesville, United States of America.
authors.forename: Suzanne
authors.initials: S
authors.lastname: Stroup
authors.affiliation: Kibong'oto Infectious Disease Hospital, Kilimanjaro, Tanzania.
authors.forename: Stellah
authors.initials: S
authors.lastname: Mpagama
authors.affiliation: Kibong'oto Infectious Disease Hospital, Kilimanjaro, Tanzania.
authors.forename: Riziki
authors.initials: R
authors.lastname: Kisonga
authors.affiliation: Kibong'oto Infectious Disease Hospital, Kilimanjaro, Tanzania.
authors.forename: Isaack
authors.initials: I
authors.lastname: Lekule
authors.affiliation: Division of Infectious Diseases and International Health, University of Virginia, Charlottesville, United States of America.
authors.forename: Jie
authors.initials: J
authors.lastname: Liu
authors.affiliation: Division of Infectious Diseases and International Health, University of Virginia, Charlottesville, United States of America.
authors.forename: Scott
authors.initials: S
authors.lastname: Heysell
mesh_terms: D000328:Adult; D002138:Calibration; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D005260:Female; D006761:Hospitals; D006801:Humans; D064704:Levofloxacin / Q000097:blood*; D008297:Male; D012044:Regression Analysis; D015203:Reproducibility of Results; D013636:Tanzania; D016896:Treatment Outcome; D018088:Tuberculosis, Multidrug-Resistant / Q000097:blood* / Q000188:drug therapy*
chemical_list: D064704:Levofloxacin