Mass fragmentographic determination of pyrazinamide and its metabolites in serum and urine.

A combined gas chromatographic-mass spectrometric technique is described for the simultaneous determination of pyrazinamide and its two main metabolites, pyrazinoic acid and 5-hydroxypyrazinoic acid. Serum (200 microliter) is deproteinized and evaporated to dryness; urine (20 microliter) is evaporated. The crude residues are silylated and selected ions are monitored in the chemical-ionization mode with isobutane as both chromatographic carrier and reagent gas. The sensitivity is 10 ng/ml for pyrazinamide and pyrazinoic acid and 20 ng/ml for the 5-hydroxy metabolite in a single analysis. Nicotinic acid and nicotinamide are internal standards. Both unchanged drug and metabolites were identified and quantified in the serum and urine of human subjects.