Direct quantitation of tenofovir diphosphate in human blood with mass spectrometry for adherence monitoring.

Inadequate adherence to chronic medications is a far-reaching problem with financial and human health consequences. By a wide margin, non-adherence is the leading cause of therapeutic failures of HIV pre-exposure chemoprophylaxis (PrEP) and antiretroviral therapy (ART). It has been proven that HIV infection can be prevented by daily dosing of emtricitabine and tenofovir disoproxil fumarate. Measurement of intracellular tenofovir diphosphate in red blood cells has been established as an effective way to assess cumulative adherence, however, the LC-MS-based analytical method developed for the purpose is both complicated and expensive. Here, we report a simple method for adherence monitoring based on direct MS quantification of intracellular tenofovir diphosphate in human whole blood. The method requires only microliters of whole blood, employs special membranes to perform plasma separation and concomitant desalting during blood collection, and uses nanoelectrospray on a triple quadrupole instrument. Quantitative performance in this proof-of-concept study includes RSDs of < 15% and successful analysis of a small number of patient samples with medium to high adherence levels. The results correlate with those of a validated LC-MS/MS method, and an R2 value of 0.9962 is achieved. This methodology has promise for extension to point-of-care testing using miniature mass spectrometers. Graphical abstract.

Method development in quantitative NMR towards metrologically traceable organic certified reference materials used as (31)P qNMR standards.

Quantitative nuclear magnetic resonance (qNMR) spectroscopy is employed by an increasing number of analytical and industrial laboratories for the assignment of content and quantitative determination of impurities. Within the last few years, it was demonstrated that (1)H qNMR can be performed with high accuracy leading to measurement uncertainties below 1 % relative. It was even demonstrated that the combination of (1)H qNMR with metrological weighing can lead to measurement uncertainties below 0.1 % when highly pure substances are used. Although qNMR reference standards are already available as certified reference materials (CRM) providing traceability on the basis of (1)H qNMR experiments, there is an increasing demand for purity assays on phosphorylated organic compounds and metabolites requiring CRM for quantification by (31)P qNMR. Unfortunately, the number of available primary phosphorus standards is limited to a few inorganic CRM which only can be used for the analysis of water-soluble analytes but fail when organic solvents must be employed. This paper presents the concept of value assignment by (31)P qNMR measurements for the development of CRM and describes different approaches to establish traceability to primary Standard Reference Material from the National Institute of Standards and Technology (NIST SRM). Phosphonoacetic acid is analyzed as a water-soluble CRM candidate, whereas triphenyl phosphate is a good candidate for the use as qNMR reference material in organic solvents. These substances contain both nuclei, (1)H and (31)P, and the concept is to show that it is possible to indirectly quantify a potential phosphorus standard via its protons using (1)H qNMR. The same standard with its assigned purity can then be used for the quantification of an analyte via its phosphorus using (31)P qNMR. For the validation of the concept, triphenyl phosphate and phosphonoacetic acid have been used as (31)P qNMR standards to determine the purity of the analyte tris(2-chloroethyl) phosphate, and the resulting purity values perfectly overlap within their expanded measurement uncertainties.

Long-term efficacy and safety of fosamprenavir plus ritonavir versus lopinavir/ritonavir in combination with abacavir/lamivudine over 144 weeks.

PURPOSE: The KLEAN study extension assessed the long-term efficacy and safety of fosamprenavir-ritonavir (FPV/r) and lopinavir-ritonavir (LPV/r), both administered with abacavir/lamivudine (ABC/3TC) fixed dose combination, over 144 weeks. METHODS: KLEAN was an open-label, noninferiority study that randomised antiretroviral-naïve patients to FPV/r twice daily (bid) or LPV/r bid with ABC/3TC once daily (qd). Patients with a viral load of <400 copies/mL at Week 48 were eligible to participate in the KLEAN study extension (up to 144 weeks) and continued with their previously randomised therapy. RESULTS: The KLEAN study extension (48 to 144 weeks) randomized 199 patients. The proportion of TLOVR responders (HIV-1 RNA <50 copies/mL) at Week 144 was 73% and 60% in the FPV/r and LPV/r arms, respectively. The proportion of TLOVR responders (<50 copies/mL) was the same irrespective of baseline HIV-1 RNA (>100,000 or 100,000 copies/mL). The Week 144 median (interquartile range) change from baseline CD4+ cell count was 300 (236-433) cells/mm3 and 335 (225-444) cells/mm3 in the FPV/r and LPV/r arms, respectively. Diarrhea was the most frequently reported adverse event. A small proportion of patients (FPV/r, 13%; LPV/r, 9%) discontinued study medication due to adverse events. Three patients (FPV/r, 1; LPV/r, 2) experienced virological failure between Week 48 and Week 144. CONCLUSION: The findings of the KLEAN study extension (48 to 144 weeks) support durable viral suppression with both FPV/r and LPV/r treatment regimens when used in combination with ABC/3TC irrespective of viral load at baseline. Both regimens were well tolerated and had similar safety profiles.

Quantification of erufosine, the first intravenously applicable alkylphosphocholine, in human plasma by isotope dilution liquid chromatography-tandem mass spectrometry using a deuterated internal standard.

A sensitive and specific liquid chromatography-tandem mass spectrometry method was developed and validated for the quantification of erucylphosphohomocholine (erufosine, ErPC(3)) in pharmacokinetic studies. Nine-fold deuterated ErPC(3) was used as the internal standard. Following protein precipitation, reversed phase chromatography was performed. For analyte detection, electrospray ionization in the positive mode was applied. The mass transition m/z 504.4>139.1 was recorded for ErPC(3), and the transition m/z 513.7>139.1 for the internal standard, respectively. Good linearity with a correlation coefficient >0.99 was found for the range of 0.48-15 mg/L ErPC(3) in plasma (0.93-29.8 microM), the important range for clinical pharmacokinetic analysis. Interassay coefficients (n=10) of variation between 4.2% and 5.5% were found for ErPC(3) pool samples with concentrations between 4.7 mg/L and 44.0mg/L, respectively. The method has been used for analyses during a phase I clinical trial of ErPC(3).