Electrochemistry of the antibacterial and antifungal drug nitroxoline and its determination in bulk form, pharmaceutical formulation and human blood.

Nitroxoline has been reduced at the mercury electrode in buffered solutions (pH 2-11) in two irreversible cathodic steps. The first step was attributed to reduction of -NO(2) group to the hydroxylamine stage and the second one to reduction-saturation of the C=N double bond. DC-polarographic and various adsorptive stripping voltammetric methods were developed for determination of nitroxoline in bulk form. Limits of quantitation of 1.02×10(-6), 3.05×10(-8), 9.01×10(-9), and 9.12×10(-10)M nitroxoline were achieved by means of the developed DC-polarography, differential-pulse-, linear-sweep-, and square-wave-adsorptive cathodic stripping voltammetric methods, respectively. All these electroanalytical methods were successfully applied for determination of nitroxoline in its Nibiol(®) tablets. While only the developed adsorptive stripping voltammetry methods were successfully applied for determination of the drug in spiked human serum and for pharmacokinetic studies in real human plasma. The analysis was carried out without interference from common excipients and without the necessity for prior extraction or interaction with any reagent during the analysis.

Determination of N-(3-nitro-4-quinoline)morpholino-4-carboxamidine in plasma high-performance liquid chromatography.

A high-performance liquid chromatographic (HPLC) method was developed for the determination of the radiosensitizing agent N-(3-nitro-4-quinoline)morpholino-4-carboxamidine (EGIS-4136) in plasma using an internal standard. HPLC separation was achieved on a LiChrosorb C18 column using acetonitrile-sodium acetate buffer (pH 7.2) (40:60) as the mobile phase and UV detection at 330 nm. The plasma samples were prepared for measurement by protein precipitation with methanol and centrifugation. The assay was validated with respect to linearity, sensitivity, accuracy, precision, stability and recovery in plasma. The limit of detection for EGIS-4136 in plasma was 0.05 microgram/ml. A straight line was obtained on plotting the peak-area ratio of EGIS-4136 to the internal standard against concentration in plasma in the range 0.1-20 microgram/ml. The method was applied to study the pharmacokinetics of EGIS-4136 in six male rats after a single oral dose of 50 mg/kg, and allowed the compound to be monitored in the concentration range 5-10 micrograms/ml occurring in rats 24 h post-administration.

High-performance liquid chromatographic analysis of nitroxoline in plasma and urine.

A high-performance liquid chromatographic method has been developed for the determination of nitroxoline in 50-microliter plasma and urine samples. A structural analogue of nitroxoline, 8-hydroxyquinoline, was added to the eluent in order to suppress peak asymmetry. Several parameters of the eluent were studied for the optimisation of the chromatographic system. Plasma concentration-time curves were constructed for three volunteers after they had received an oral dose of 100 mg of nitroxoline. Plasma half-life was about 1 h. Within 12 h, about 1% of the dose was excreted in the urine as free nitroxoline and about 30% as conjugated metabolite of the parent compound.

Clinical pharmacokinetics of nitroxoline.

14C-Nitroxoline was given orally to the rats, and its distribution as well as plasma and bile levels were determined autoradiographically and by the aid of radioactivity measurements, respectively. Nitroxoline was also given to the human volunteers orally and intravenously in three various doses and the corresponding urine concentrations of unconjugated and conjugated nitroxoline were determined spectrophotometrically. A pharmacokinetical model was generated on the basis of the results. The curve fitting procedure between total nitroxoline cumulative quantities in urine and the model response simulated on analog-hybrid computer enabled the evaluation of the validity of the chosen model as well as of the identification of its parameters.

Determination of oxamniquine in serum.

A method for the analysis of oxamniquine in serum (or plasma), sensitive to 10 ng/ml, was developed. Oxamniquine and a close structural analog as the internal standard were extracted from serum with ether. After derivatization with N,O-bis(trimethylsilyl)acetamide, oxamniquine was determined as its trimethylsilyl ether derivative by GLC using an electron-capture detector. The method was developed to study serum concentration profiles of different dosage forms of oxamniquine.