Sensitive biomonitoring of monoterpene exposure by gas chromatographic-mass spectrometric measurement of hydroxy terpenes in urine

An isocratic reversed-phase high-performance liquid chromatographic method with ultraviolet detection at 205 nm has been validated for the determination of indinavir, ritonavir and lopinavir (ABT 378) in human plasma. The ritonavir analogue A-86093.0 was used as internal standard. Good chromatographic separation was achieved using a stainless steel column packed with 5 microm Phenomenex phenyl hexyl material operated at 40 degrees C, and a mobile phase consisting of acetonitrile-10 mM potassium phosphate buffer (50:50, v/v). The calibration curve for indinavir was linear over the range of 50 to 1000 microg/l while the ritonavir and lopinavir calibration curves were linear over the range of 100 to 15,000 microg/l. The lower limit of quantitations for indinavir, ritonavir and lopinavir were 50, 100 and 100 microg/l, respectively, using 500 microl of human plasma. The validation data showed that the assay is sensitive, specific and reproducible for determination of indinavir, ritonavir and lopinavir. This method is being used in a therapeutic drug monitoring service to quantitate these therapeutic agents in patients infected with human immunodeficiency virus.