Reliable and sensitive determination of dutasteride in human plasma by liquid chromatography-tandem mass spectrometry

LC-MS/MS determination of dutasteride and its major metabolites in human plasma

Dutasteride is a specific and selective inhibitor of both 5α-reductase isoforms used mainly in benign prostatic hyperplasia and lower urinary tract symptoms. Although the drug is extensively metabolized in humans, data on the concentrations of its main metabolites are lacking. There is also a lack of data on dutasteride stability in frozen plasma samples. Our method was used to determine dutasteride and its active metabolites: 4'-hydroxydutasteride, 6β-hydroxydutasteride, and 1,2-dihydrodutasteride in plasma after a single administration of 0.5 mg of dutasteride. We also assessed the long-term stability (two years in the freezer) of dutasteride in clinical samples. The developed method covered the range of 0.1-3.5 ng/mL for dutasteride and 0.08-1.2 ng/mL for 1,2-dihydrodutasteride, 4'-hydroxydutasteride, 6β-hydroxydutasteride. It was proved to be reliable as it met all validation criteria required by the European Medicine Agency for bioanalytical methods. 4'-hydroxydutasteride and 1,2-dihydrodutasteride concentrations in plasma were higher than 6β-hydroxydutasteride. Dutasteride was stable in the freezer for up to 2 years in clinical samples. Thus within 1014 days of storage (below - 65 °C), samples can be reanalyzed without the risk of unreliable results.

Inhibition of 5α-reductase alters pregnane metabolism in the late pregnant mare

In the latter half of gestation in the mare, progesterone concentrations decline to near undetectable levels while other 5α-reduced pregnanes are elevated. Of these, 5α-dihydroprogesterone and allopregnanolone have been reported to have important roles in either pregnancy maintenance or fetal quiescence. During this time, the placenta is necessary for pregnane metabolism, with the enzyme 5α-reductase being required for the conversion of progesterone to 5α-dihydroprogesterone. The objectives of this study were to assess the effects of a 5α-reductase inhibitor, dutasteride on pregnane metabolism (pregnenolone, progesterone, 5α-dihydroprogesterone, 20α-hydroxy-5α-pregnan-3-one, 5α-pregnane-3β,20α-diol and allopregnanolone), to determine circulating dutasteride concentrations and to assess effects of dutasteride treatment on gestational parameters. Pregnant mares (n = 5) received dutasteride (0.01 mg/kg/day, IM) and control mares (n = 4) received vehicle alone from 300 to 320 days of gestation or until parturition. Concentrations of dutasteride, pregnenolone, progesterone, 5α-dihydroprogesterone, 20α-hydroxy-5α-pregnan-3-one, 5α-pregnane-3β,20α-diol, and allopregnanolone were evaluated via liquid chromatography–tandem mass spectrometry. Samples were analyzed as both days post treatment and as days prepartum. No significant treatment effects were detected in pregnenolone, 5α-dihydroprogesterone, 20α-hydroxy-5α-pregnan-3-one, 5α-pregnane-3β,20α-diol or allopregnanolone for either analysis; however, progesterone concentrations were increased (P < 0.05) sixfold in dutasteride-treated mares compared to control mares. Dutasteride concentrations increased in the treated mares, with a significant correlation (P < 0.05) between dutasteride concentrations and pregnenolone or progesterone concentrations. Gestational length and neonatal outcomes were not significantly altered in dutasteride-treated mares. Although 5α-reduced metabolites were unchanged, these data suggest an accumulation of precursor progesterone with inhibition of 5α-reductase, indicating the ability of dutasteride to alter progesterone metabolism.

Systematic evaluation of plasma phospholipids for reliable and precise determination of dronedarone and desbutyldronedarone by LC–MS/MS

Background: The objective of the present work was to minimize or eliminate the matrix effect due to plasma phospholipids as observed during sample preparation for accurate determination of dronedarone and its active metabolite, desbutyldronedarone by LC–ESI-MS/MS. Results: The extraction recovery and matrix factors ranged from 93.27 to 95.14% and 0.99 to 1.02, respectively, for both the analytes. A linear concentration range of 0.10 to 150 ng/ml was established for both the analytes. The analytes were efficiently resolved (Rs 2.37) on Kromasil® (AkzoNobel, Bohus, Sweden) C18 column within 3.0 min. The assay reproducibility was determined by reanalysis of 72 incurred samples with % change within ±10%. Conclusion: The optimized solid-phase extraction provided cleaner extracts with reduced matrix effect from plasma phospholipids compared with protein precipitation and liquid–liquid extraction.