Validation of a sensitive LC/MS/MS method for the determination of zidovudine and lamivudine in human plasma

Abstract

A sensitive LC/MS/MS assay for determining zidovudine (ZDV) and lamivudine (3TC) in human plasma was validated to support antiretroviral pharmacology research programs. After addition of stable labeled isotopic zidovudine (ZDV-IS) and lamivudine (3TC-IS) as internal standard, a solid-phase extraction was performed with an Oasis HLB 1 cm(3) cartridge, with recoveries of 92.3% for ZDV and 93.9% for 3TC. A Phenomonex Synergi Hydro-RP (2.0 ×150 mm) reversed-phase analytical column was utilized for chromatographic separation. The mobile phase consisted of an aqueous solution of 15% acetonitrile and 0.1% acetic acid. Detection was accomplished by ESI/MS/MS in the positive ion mode, monitoring 268/127, 271/130, 230/112 and 233/115 transitions, for ZDV, ZDV-IS, 3TC and 3TC-IS, respectively. The method was linear from 1 to 3000 ng/mL with a minimum quantifiable limit of 1 ng/mL when 100 μL of plasma was analyzed. Validation results demonstrated high accuracy (≤8.3% deviation) and high precision (≤10% CV) for the quality control samples. The method was also shown to be specific and reproducible. The value of the high sensitivity was demonstrated by quantitation of approximately 100 existing samples that had ZDV below the limit of quantitation using a previously validated, less sensitive HPLC-UV method utilized in the laboratory.

Conflict of interest statement

Conflict of Interest: None to declare.

Copyright © 2011 John Wiley & Sons, Ltd.

Figures

Figure 1

Chemical structure of (A) zidovudine (MW 267) and (B) lamivudine (MW 229).

Figure 2

Representative LC/MS/MS chromatograms. (A) blank plasma sample; (B) blank plasma sample spiked with ZDV/3TC at the LLOQ (1.0 ng/mL) and internal standard; and (C) a subject unknown sample. The top chromatogram is the analyte while the bottom chromatogram is the internal standard; 3TC elutes first and is in the left chromatograms, followed by ZDV in the right chromatograms. The unknown subject sample (C) shows a peak retained at 5.65 minutes, which may be due to the presence of an ZDV 5′ glucuronide metabolite formed in vivo, which is separated from ZDV chromatographically and degraded in the MS/MS ESI source.

Figure 2

Representative LC/MS/MS chromatograms. (A) blank plasma sample; (B) blank plasma sample spiked with ZDV/3TC at the LLOQ (1.0 ng/mL) and internal standard; and (C) a subject unknown sample. The top chromatogram is the analyte while the bottom chromatogram is the internal standard; 3TC elutes first and is in the left chromatograms, followed by ZDV in the right chromatograms. The unknown subject sample (C) shows a peak retained at 5.65 minutes, which may be due to the presence of an ZDV 5′ glucuronide metabolite formed in vivo, which is separated from ZDV chromatographically and degraded in the MS/MS ESI source.

Figure 2

Representative LC/MS/MS chromatograms. (A) blank plasma sample; (B) blank plasma sample spiked with ZDV/3TC at the LLOQ (1.0 ng/mL) and internal standard; and (C) a subject unknown sample. The top chromatogram is the analyte while the bottom chromatogram is the internal standard; 3TC elutes first and is in the left chromatograms, followed by ZDV in the right chromatograms. The unknown subject sample (C) shows a peak retained at 5.65 minutes, which may be due to the presence of an ZDV 5′ glucuronide metabolite formed in vivo, which is separated from ZDV chromatographically and degraded in the MS/MS ESI source.

Figure 3

Graph showing the correlation of ZDV samples (n=27) analyzed by HPLC-UV (x axis) and LC/MS/MS (y axis). Square points indicate samples (n=9/27) that were reported as below limit of quantitation by the UV method.

Figure 4

Graph showing the correlation of 3TC samples (n=27) analyzed by HPLC-UV (x axis) and LC/MS/MS (y axis).