Telcagepant (MK-0974) is a novel oral calcitonin gene-related peptide (CGRP) 
receptor antagonist and is currently under clinical development. Results from 
phases II and III clinical trials have suggested that telcagepant is effective 
for migraine treatment. A reliable and high throughput protein precipitation 
(PPT) method for determination of telcagepant in human plasma using liquid 
chromatography coupled with atmospheric pressure chemical ionization (APCI) 
tandem mass spectrometry has been developed. Clinical samples, internal standard 
(IS) and acetonitrile are transferred into 96-well plates using a robotic liquid 
handling system. An aliquot of 10 microL supernatant is directly injected into 
the LC-MS/MS system where separation is performed on a FluoPhase RP (150 x 
2.1mm, 5 microm) column with an isocratic mobile phase (60% acetonitrile with 
0.1% formic acid and 40% water with 0.1% formic acid) at 0.2 mL/min. The 
interfering 3S-diastereomer of telcagepant, which is observed in clinical 
samples, is chromatographically resolved from telcagepant. The PPT procedure 
significantly reduces the time required for sample processing and the assay is 
sufficiently sensitive for detection using both API 4000 and API 3000 mass 
spectrometers. The linear calibration range is 5-5000 nM using 200 microL of 
plasma. Assay intraday validation was conducted using six calibration curves 
derived from six lots of human control plasma. Calibration standard accuracy did 
not deviate by more than 3% and 6% of nominal values, and precision did not 
exceed 4% coefficient of variation (CV) and 10% CV, respectively on the API 4000 
and API 3000. Several clinical phases IIb and III studies have been successfully 
supported with this assay.