[HPLC determination of diprafenone and its active metabolite 5-hydroxydiprafenone in human plasma]

A simple, specific and sensitive HPLC method is described, which allows the quantitation of diprafenone and its active metabolite 5-hydroxydiprafenone in human plasma. Propafenone is used as internal standard. After extraction by diethyl ether from plasma, the analytes are reextracted with 5% phosphoric acid from the organic phase. Chromatographic separation on a RP-18 column and UV detection (220 nm) allows the sensitive determination of diparafenone and 5-hydroxydiprafenone in plasma with a lower limit of quantitation of 5.0 ng/ml for both substances. The method was successfully applied to human plasma samples from 24 subjects after oral or i.v. administration of 300 mg or 50 mg diprafenon hydrochloride, respectively.