Validation of a simple isocratic HPLC-UV method for rifampicin and isoniazid quantification in human plasma

A simple and selective reversed phase HPLC-UV method for rifampicin and isoniazid quantification in human plasma was developed and validated. The method consisted of drug extraction with trichloroacetic acid and organic solvent followed by derivatization of isoniazid. Using an isocratic mode, rifampicin was analyzed on a C18 (250 × 4.6 mm, 5 μm) column at 339 nm, while isoniazid was analyzed on a C8 (250 × 4.6 mm, 5 μm) column at 273 nm. All validation parameters fulfilled the FDA requirements, as the method was accurate (bias% < 10.26), precise (CV% < 10.39) and linear from 0.31 to 37.80 μg/mL of rifampicin and 0.89 to 71.36 μg/mL of isoniazid. The samples remained stable during the usual processing and analysis times and also during the two freeze/thaw cycles. The recovery of both analytes was reproducible (CV% < 11.2) in the range of 97.3-99.6% of rifampicin and 89.8-96.6% of isoniazid. The low volume of plasma necessary for the quantification of the samples (750 μL in total) and the low limit of quantification (0.31 μg/mL for rifampicin and 0.89 μg/mL for isoniazid) made this method useful for carrying out pharmacokinetic tests both in humans or animal models. In addition, the method can be successfully applied for bioavailability studies or drug monitoring in tuberculosis treatment.