High pressure liquid chromatographic determination and biophamaceutical studies of 9-methoxycanthin-6-one from eurycoma longifolia jack
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Date
2004-01
Authors
Saadiah, Tan
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Abstract
A specific and sensitive reversed phase high performance liquid chromatography
method using fluorescence detection was developed to determine quantitatively the
plasma concentration of 9-methoxycanthin-6-one in biopharmaceutical studies. The
HPLC method entailed direct injection of plasma sample onto the column after
deproteinization using acetonitrile. The mobile phase comprised acetonitrile arid
distilled water (55 : 45, v/v). Analysis was run at a flow rate of 1.0 ml/min with the
detector operating at an excitation wavelength of 371 nm and emission wavelength of
504 nm. The linearity curve was in the range of 1.6 ng/ml to 1600 ng/ml with the
detection limit of 0.6 ng/ml. The mean recovery was approximately 108 %. The
accuracy and precision of between-day and within-day were all less than 12 %. The
compound, 9-methoxycanthin-6-one was isolated from the roots of Eurycoma
longifolia Jack by sequential extraction and acid-base extraction methods followed by
various chromatographic techniques. The pure compound was characterised using
ultraviolet, infrared and nuclear magnetic resonance spectroscopies. Biopharmaceutical
studies were then conducted on the compound using rats. The oral absolute
bioavailability of the 9-methoxycanthin-6-one determined using oral and intravenous
administrations revealed that it was poorly absorbed, with bioavailability of less than 1
%. The mean T max and Cmax values obtained from the oral route were 0.50 ± 0.19 hr and
30.33 ± 10.61 ng/ml respectively while the mean volume of distribution estimated from
intravenous data was 0.049 L/kg. The intravenous plasma profile of the compound
exhibited a two-compartment phannacokinetic behaviour, with an initial fast
distribution phase followed by a slower elimination phase. Finally, investigations were
also carried out to determine various factors that could result in the poor oral
bioavailability observed, which included studying the chemical stability of the
compound and the influence ofP-gp and CYP3A4 in its absorption. The compound was
found to be stable, with no appreciable degradation detected in pH 1, 4 and 7. From the
in vivo study using ketoconazole as inhibitor of CYP3A4 and P-gp, the result revealed
that 9-methoxycanthin-6-one might be a substrate of CYP3A4 and P-gp when
administered orally but merits further studies using a larger number of rats.
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Keywords
Liquid chromatographic determination , 9-methoxycanthin-6-one