A HPLC-MS method to detect and quantify guanfacine in urine.

BACKGROUND: Guanfacine, an α2-adrenergic α2A)agonist long indicated to treat hypertension, is now being used to treat attention deficit-hyperactivity disorder (ADHD) in adolescents. This new therapeutic use may require urine testing to document compliance or abuse. A simple rapid high pressure liquid chromatography-mass spectrometry (HPLC-MS) method to detect and quantify guanfacine in urine following therapeutic administration is presented. METHODS: Guanfacine and protriptyline internal standard were extracted from alkalinized urine with ethyl acetate. The organic layer was evaporated, reconstituted with mobile phase and analyzed on a YMC Basic S-5 micron, 2.0 × 150 mm HPLC column connected to an MS detector operated in positive electrospray ionization mode with selected ion resonance. Elution times were <5 min. RESULTS: The analytical measurement range for guanfacine was 20-2000 ng/mL. The limit of detection and quantitation were 5 ng/mL and 20 ng/mL, respectively. Precision as %CV was <15% at 40, 100 and 500 ng/mL (n=6). Percentage recovery using the same concentrations was >89%. Interference with drugs and biological constituents was assessed; no interferences were noted. Analysis of 100 random post-diagnostic urine specimens yielded 11 guanfacine positive results with concentrations ranging from 11 to 6390 ng/mL. CONCLUSIONS: This HPLC-MS method provides a simple and rapid method for the routine detection and quantitation of guanfacine in urine specimens.

A novel method for the determination of guanfacine in urine by gas chromatography-mass spectrometry.

Guanfacine (Tenex), an antihypertensive available since 1975, has recently been indicated for the treatment of attention deficit hyperactivity disorder in children (Intuniv). Because of this new usage, a gas chromatography-mass spectrometry method was developed and validated for the determination of guanfacine in urine. Guanfacine and 100 ng of protriptyline (internal standard) were extracted from 1.0 mL urine with 0.5 mL of saturated carbonate/bicarbonate buffer and 2 mL of ethyl acetate. The solvent extract was evaporated and derivatized with heptaflurobutyric anhydride in n-butyl chloride. Chromatographic separation was achieved using a DB-5 capillary column (30 m x 0.32 mm, 0.25 microm). Ions monitored for guanfacine were m/z 86.1, 272.1, and 274.1, and ions monitored for protriptyline were m/z 191.1 and 189.1. Concentrations were determined using calibrators over the range of 0.1-2.0 mg/L. The linear regression for all calibration curves had r2 values > or = 0.99. The limit of detection was 0.05 mg/L; limit of quantitation was 0.1 mg/L; and upper limit of linearity was 10.0 mg/L. Percent recovery of guanfacine at 0.1 and 2.0 mg/L was 93% and 71%, respectively. The method was found acceptable for routine quantitative analysis of guanfacine in urine.