Article

Determination of lumefantrine in small-volume human plasma by LC-MS/MS: using a deuterated lumefantrine to overcome matrix effect and ionization saturation.

Drug Research Unit, Department of Clinical Pharmacy, School of Pharmacy, University of California, San Francisco, CA 94110, USA.
Bioanalysis (Impact Factor: 3.25). 01/2012; 4(2):157-66. DOI: 10.4155/bio.11.303
Source: PubMed

ABSTRACT To support pediatric study, a method to determine lumefantrine (LF) with small sample volume is needed. Matrix effect (ME) is a daunting issue in LF quantification in human plasma with LC-MS/MS.
Here we report an LC-MS/MS method with a deuterated LF as the internal standard (IS). Plasma sample (25 µl) was acidified with 5% formic acid prior to extraction with ethyl acetate. The recovery was over 80%. The absolute ME was within the range of 100 ± 8% for both LF and the IS, but cumulative ME was observed via large variation of IS signal. The cumulative ME and ionization saturation were overcome with the co-eluting LF-D(9) as the IS. The linear range of calibration curve was 50-20,000 ng/ml.
ME and ionization saturation was overcome with a deuterated IS. The method utilized a small sample volume, suitable for pediatric study with capillary tube blood collection method.

1 Bookmark
 · 
160 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The linear range of a liquid chromatography/tandem mass spectrometry (LC/MS/MS) bioanalytical assay is typically about three orders of magnitude. A broader standard curve range is favored since it can significantly reduce the time, labor and potential errors related to sample dilution - one of the bottlenecks in sample analysis. Using quadratic regression to fit the standard curve can, to a certain degree, extend the dynamic range. However, the use of a quadratic regression is controversial, particularly in regulated bioanalysis. A number of compounds, with different physicochemical properties and ionization efficiencies, were evaluated to understand the cause of the non-linear behavior of the standard curve. The standard curve behavior is primarily associated with the absolute analyte response but not the analyte concentration, the properties of the analyte, or the nature of the matrix when a stable-isotope-labeled internal standard (SIL-IS) is used. For all the test compounds, a non-linear curve was observed when signals exceeded a certain response, which depends on the detector used in the mass spectrometer. With typical API4000 instruments used for the experiments, this critical response level was determined to be ~1 E+6 counts per second (cps) and it was successfully used to predict the linear ranges for the test compounds. By simultaneously monitoring two selective reaction monitoring (SRM) channels of different intensity and using SIL-IS, a linear range of five orders of magnitude was achieved. In this work, the root cause of the non-linear behavior of the standard curve when using a SIL-IS was investigated and identified. Based on the findings, an improved multiple SRM channels approach was proposed and successfully applied to obtain a linear dynamic range of five orders of magnitude for one test compound. This approach may work particularly well for LC/MS/MS bioanalytical assay of dried blood spot (DBS) samples, for which a direct dilution is cumbersome.
    Rapid Communications in Mass Spectrometry 06/2012; 26(12):1465-74. · 2.51 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Background Human immunodeficiency virus (HIV) protease inhibitors show activity against Plasmodium falciparum in vitro. We hypothesized that the incidence of malaria in HIV-infected children would be lower among children receiving lopinavir-ritonavir-based antiretroviral therapy (ART) than among those receiving nonnucleoside reverse-transcriptase inhibitor (NNRTI)-based ART. Methods We conducted an open-label trial in which HIV-infected children 2 months to 5 years of age who were eligible for ART or were currently receiving NNRTI-based ART were randomly assigned to either lopinavir-ritonavir-based ART or NNRTI-based ART and were followed for 6 months to 2 years. Cases of uncomplicated malaria were treated with artemether-lumefantrine. The primary end point was the incidence of malaria. Results We enrolled 176 children, of whom 170 received the study regimen: 86 received NNRTI-based ART, and 84 lopinavir-ritonavir-based ART. The incidence of malaria was lower among children receiving the lopinavir-ritonavir-based regimen than among those receiving the NNRTI-based regimen (1.32 vs. 2.25 episodes per person-year; incidence-rate ratio, 0.59; 95% confidence interval [CI], 0.36 to 0.97; P=0.04), as was the risk of a recurrence of malaria after treatment with artemether-lumefantrine (28.1% vs. 54.2%; hazard ratio, 0.41; 95% CI, 0.22 to 0.76; P=0.004). The median lumefantrine level on day 7 after treatment for malaria was significantly higher in the lopinavir-ritonavir group than in the NNRTI group. In the lopinavir-ritonavir group, lumefantrine levels exceeding 300 ng per milliliter on day 7 were associated with a reduction of more than 85% in the 63-day risk of recurrent malaria. A greater number of serious adverse events occurred in the lopinavir-ritonavir group than in the NNRTI group (5.6% vs. 2.3%, P=0.16). Pruritus occurred significantly more frequently in the lopinavir-ritonavir group, and elevated alanine aminotransferase levels significantly more frequently in the NNRTI group. Conclusions Lopinavir-ritonavir-based ART as compared with NNRTI-based ART reduced the incidence of malaria by 41%, with the lower incidence attributable largely to a significant reduction in the recurrence of malaria after treatment with artemether-lumefantrine. Lopinavir-ritonavir-based ART was accompanied by an increase in serious adverse events. (Funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development; ClinicalTrials.gov number, NCT00978068 .).
    New England Journal of Medicine 11/2012; 367(22):2110-8. · 54.42 Impact Factor

Full-text (2 Sources)

View
20 Downloads
Available from
Jun 2, 2014