Simultaneous Analysis of Tramadol, O-Desmethyltramadol, and N-Desmethyltramadol Enantiomers in Rat Plasma by High-Performance Liquid Chromatography-Tandem Mass Spectrometry: Application to Pharmacokinetics

Tramadol (T) is available as a racemic mixture of (+)-trans-T and (-)-trans-T. The main metabolic pathways are O-demethylation and N-demethylation, producing trans-O-desmethyltramadol (M1) and trans-N-desmethyltramadol (M2) enantiomers, respectively. The analgesic effect of T is related to the opioid activity of (+)-trans-T and (+)-M1 and to the monoaminergic action of (+/-)-trans-T. This is the first study using tandem mass spectrometry as a detection system for the simultaneous analysis of trans-T, M1, and M2 enantiomers. The analytes were resolved on a Chiralpak (R) AD column using hexane: ethanol (95.5:4.5, v/v) plus 0.1% diethylamine as the mobile phase. The quantitation limits were 0.5 ng/ml for trans-T and M1 and 0.1 ng/ml for M2. The method developed and validated here was applied to a pharmacokinetic study in rats. Male Wistar rats (n = 6 at each time point) received a single oral dose of 20 mg/kg racemic trans-T. Blood samples were collected up to 12 h after drug administration. The kinetic disposition of trans-T and M2 was enantioselective (AUC((+)/(-)) ratio = 4.16 and 6.36, respectively). The direction and extent of enantioselectivity in the pharmacokinetics of trans-T and M2 in rats were comparable to data previously reported for healthy volunteers, suggesting that rats are a suitable model for enantioselective studies of trans-T pharmacokinetics. Chirality 23: 287-293, 2011. (C) 2010 Wiley-Liss, Inc.

Courtyard, Hill House, Chapel Hill, Brisbane

Central courtyard space. Door to master bedroom and ensuite on right.

Upper west elevation, Hill House, Chapel Hill, Brisbane

Ensuite corner window in foreground on right, with planter to garden on left.

Trusses, Hill House, Chapel Hill, Brisbane

Trusses to living room roof.

Garden, Hill House, Chapel Hill, Brisbane

As seen from master bedroom, looking across to living room.

Garage, Hill House, Chapel Hill, Brisbane

Garage with store above (south elevation).

Courtyard, Hill House, Chapel Hill, Brisbane

Central courtyard space with strip windows to kitchen/dining on left.

Kitchen, Hill House, Chapel Hill, Brisbane

Dining room and courtyard space beyond.

Courtyard, Hill House, Chapel Hill, Brisbane

Courtyard to west elevation at completion of construction. Planter in foreground to right.

Courtyard, Hill House, Chapel Hill, Brisbane

Paved courtyard area to Western elevation.

West elevation, Hill House, Chapel Hill, Brisbane

As seen from the street, looking north-east.

Door openings, Hill House, Chapel Hill, Brisbane

Openings under construction.

Fireplace, Hill House, Chapel Hill, Brisbane

Fireplace to living room.

Entry hallway, Hill House, Chapel Hill, Brisbane

As seen from top of stairs.

Entry, Hill House, Chapel Hill, Brisbane

Entry stairs and front door, with garden area beyond.