Therapeutic monitoring of antituberculosis drugs by direct in-line extraction on a high-performance liquid chromatography system

A direct in-line pre-column extraction technique in which guanidinium and ammonium sulfate are used, followed by column switching, was employed to analyze serum, plasma and cerebrospinal fluid samples of patients treated for tuberculous meningitis. Resolution of a wide range of polar to non-polar xenobiotics was obtained on a C₈ silica column by using a linear gradient from a binary system consisting of solvent A (0.05 M KH₂PO₄) and solvent B (acetonitrile—isopropanol, 4:1, v/v). Apart from the anti-tuberculosis drugs (isoniazid, pyrazinamide, ethionamide and rifampicin) the patients received up to sixteen different medicines for prevention of complications and the treatment of symptoms. Qualitative resolution of all the drugs was obtained by the chromatographic system. Quantitation of pyrazinamide and ethionamide was achieved with high precision and low inter-sample variation.