Quantification of pyrazinamide and its metabolites in plasma by ionic-pair high-performance liquid chromatography. Implications for the separation mechanism

Pyrazinamide, the amide of pyrazinoic acid, is one of the basic therapeutic agents currently used in combination for chemotherapy of tuberculosis. A reversed-phase high-performance liquid chromatography method based on ionic pair chromatography, was developed after solid-phase extraction of the analytes from plasma with prior addition of internal standard. The main metabolites, pyrazinoic acid, 5-hydroxypyrazinoic acid and 5-hydroxypyrazinamide, were included as well as uric acid and other purine derivatives to allow detailed study of the pharmacokinetics of the drug, especially in patients with impaired kidney function. Some interesting features of the chromatographic system giving some insight in the retention mechanism and of the solid-phase extraction are discussed in detail.

Determination of pyrazinamide and its main metabolites in rat urine by high-performance liquid chromatography

A new high-performance liquid chromatograhic procedure for simultaneous determination of pyrazinamide (PZA) and its three metabolites 5-hydroxypyrazinamide (5-OH-PZA), pyrazinoic acid (PA), and 5-hydroxypyrazinoic acid (5-OH-PA), in rat urine was developed. 5-OH-PZA and 5-OH-PA standards were obtained by enzymatic synthesis (xanthine oxidase) and checked by HPLC and GC-MS. Chromatographic separation was achieved in 0.01 M KH2PO4 (pH 5.2), circulating at 0.9 ml/min, on a C18 silica column, at 22 degrees C. The limits of detection were 300 microg/l for PZA, 125 microg/l for PA, 90 microg/l for 5-OH-PZA and 70 microg/l for 5-OH-PA. Good linearity (r2>0.99) was observed within the calibration ranges studied: 0.375-7.50 mg/l for PZA, 0.416-3.33 mg/l for PA, 0.830-6.64 mg/l for 5-OH-PZA and 2.83-22.6 mg/l for 5-OHPA. Accuracy was always lower than +/- 10.8%. Precision was in the range 0.33-5.7%. The method will constitute a useful tool for studies on the influence of drug interactions in tuberculosis treatment.