title: Quantification of free mycophenolic acid and its glucuronide metabolite in human plasma by liquid-chromatography using mass spectrometric and ultraviolet absorbance detection.
abstract: The immunosuppressant drug mycophenolic acid (MPA) and its major metabolite, mycophenolic acid glucuronide (MPAG), are highly bound to albumin. An HPLC-tandem-MS (HPLC/MS/MS) and an HPLC-UV assay were developed to measure free (unbound) concentrations of MPA and MPAG, respectively. Ultrafiltrate was prepared from plasma (500 microl) by ultrafiltration at 3000 x g for 20 min (20 degrees C). Both MPA and MPAG were isolated from ultrafiltrate (100 microl) by acidification and C18 solid-phase extraction. Free MPA was measured by electrospray tandem mass spectrometry using selected reactant monitoring (MPA: m/z 338.2--> 206.9) in positive ionisation mode. Chromatography was performed on a PFPP column (50 mm x 2 mm, 5 microm). Total analysis time was 7 min. The assay was linear over the range 1-200 microg/l with a limit of quantification of 1 microg/l. The inter-day accuracy and imprecision of quality controls (7.5, 40, 150 microg/l) were 94-99% and < 7%, respectively. Free MPAG was chromatographed on a C18 Nova-Pak column (150 mm x 3.9 mm, 5 microm) using a binary gradient over 20 min. The eluent was monitored at 254 nm. The assay was linear over the range 1-50 mg/l with the limit of quantification at 2.5 mg/l. The inter-day accuracy and imprecision of quality controls (5, 20, 45 mg/l) was 101-107% and < 8% (n = 4), respectively. For both methods no interfering substances were found in ultrafiltrate from patients not receiving MPA. The methods described have a suitable dynamic linear range to facilitate the investigation of free MPA and MPAG pharmacokinetics in transplant patients. Further, this is the first reported HPLC-UV method to determine free MPAG concentrations.
authors.affiliation: School of Pharmacy, University of Queensland, Brisbane, Qld., Australia. batcheson@soms.uq.edu.au
authors.forename: Bronwyn
authors.initials: B
authors.lastname: Atcheson
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Taylor
authors.forename: David W
authors.initials: DW
authors.lastname: Mudge
authors.forename: David W
authors.initials: DW
authors.lastname: Johnson
authors.forename: Peter I
authors.initials: PI
authors.lastname: Pillans
authors.forename: Susan E
authors.initials: SE
authors.lastname: Tett
mesh_terms: D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D006801:Humans; D009173:Mycophenolic Acid / Q000097:blood*; D012680:Sensitivity and Specificity; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D013056:Spectrophotometry, Ultraviolet / Q000379:methods*
chemical_list: D009173:Mycophenolic Acid