Quantification of piroxicam and 5′-hydroxypiroxicam in human plasma and saliva using liquid chromatography–tandem mass spectrometry following oral administration

• Human plasma and saliva samples used for pharmacokinetics studies.
• Validation methods of piroxicam and 5′-hydroxypiroxicam extraction in plasma and saliva.
• Piroxicam and 5′-hydroxypiroxicam in saliva samples can be quantified using LC–MS/MS.

Saliva sampling used to quantify piroxicam and 5′-hydroxypiroxicam is a noninvasive and painless method when compared to sequential blood sampling. For that, a rapid, selective and sensitive liquid chromatography–tandem mass spectrometric method for simultaneous determination of piroxicam and 5′-hydroxypiroxicam in saliva and human plasma was developed and validated. Piroxicam and its major metabolite were separated using a LiChroCART 125-4 RP Select-B Sorbent C18 column using a mixture of methanol and 2% phosphoric acid (pH 2.7) (70:30, v/v) for the mobile phase with a flow injection of 1 mL/min. The run time was 4 min. Volunteers had saliva and blood sampled before, 1, 2, 3, 4, 5, 6, 8, 11, 24, 48 and 72 h after taking a 20 mg oral dose of piroxicam. The pharmacokinetic parameters of piroxicam in plasma samples were as follows: AUC0−72 (64819 h ng/mL), predicted clearance (0.2 L/h), distribution volume (14.8 L), elimination half-life (50.7 h) and saliva/plasma concentration ratio (0.003). The estimation of all pharmacokinetic parameters for 5′-hydroxypiroxicam would require collections beyond 72 h; however, it was possible to quantify the mean maximum concentration (133 ng/mL), time to peak concentration (53.6 h), mean AUC0−72 (6213 h ng/mL), predicted clearance (110.3 L/h) and saliva/plasma concentration ratio (0.04). The developed methods proved effective and sensitive for determining the lower quantification limit of piroxicam in plasma (6.1 ng/mL) and saliva (0.15 ng/mL) and of 5′-hydroxypiroxicam in plasma (1.2 ng/mL) and saliva (0.15 ng/mL).