A validated HPLC method for the simultaneous determination of naftidrofuryl oxalate and its degradation product (metabolite), naftidrofuryl acid: applications to pharmaceutical tablets and biological samples

A simple, sensitive, and selective reverse phase-high performance liquid chromatography (RP-HPLC) method was developed and validated for the simultaneous determination of naftidrofuryl oxalate (NF) and its hydrolytic degradation product (metabolite), naftidrofuryl acid (NFA). Chromatographic separation was achieved on Spheri-5 RP-C8 (5 µm) (220 × 4.6 mm i.d.) column using a mobile phase composed of acetonitrile, 0.05 M sodium acetate and triethylamine (40 : 60 : 0.1, by volume) adjusted to pH 5.5 using glacial acetic acid. The mobile phase was pumped at flow rate 1.5 ml/min. The UV detector was set at 225 nm and quantification of the analytes was based on measuring the peak areas. The method was proved to be accurate and precise with linearity ranges of 0.1-25 and 0.2-25 µg ml(-1) for NF and NFA, respectively. The limits of detection were 0.03 and 0.04 µg ml(-1) for NF and NFA, respectively. The method was applied to serve three goals: (1) stability-indicating assay of the parent drug NF in its pharmaceutical formulation, (2) determination of the degradation product NFA down to a level of 0.005% in the presence of large excess of the parent drug, and (3) drug monitoring of naftidrofuryl and its metabolite, naftidrofuryl acid, in human plasma/urine samples taken from a healthy volunteer treated with 200 mg oral dose of naftidrofuryl oxalate. The proposed method proved to be accurate, precise, and reliable in all these application fields.