The REMEDI™ will no longer be supported. Therefore, we had to introduce a new procedure for the general unknown screening. We introduced the GC-MS screening procedure published by Maurer et al. (1) and compared its performance with the REMEDI™ for the four different drug classes: antidepressants, antipsychotics, non-opioid analgesics and anticonvulsants.
Half of the urine sample has been hydrolysed by acid hydrolyses and then been combined
with the other half. Trimipramine-d3 has been added as internal standard and liquid-liquid extraction was performed with dichloromethane/ isopropanol/ethylacetate. The organic phase was evaporated and the residue derivatized with acetanhydride/pyridine using microwave energy.
After evaporation, the residue was dissolved in 50 μl toluene/ethylacetat
e and injected into a TraceTM GC 2000 coupled to a MD 800 mass spectrometer (ThermoQuest, San José, USA). With the exception of sertraline, all antidepressants used in Switzerland could be detected with both methods below the concentration usually found in urine after therapeutic use (cU). The GC-MS procedure had a higher sensitivity for all compounds analysed. Many antipsychotic drugs are only minimally excreted in urine as unchanged drug. Therefore, the detection limit of the
parent drug was often much higher than the cU. The metabolites however could be detected
sufficiently. With the exception of amisulpride, sulpiride and tiapride, all antipsychotics had a
higher sensitivity with the GC-MS procedure.
The non-opioid analgesics and anticonvulsants can only incompletely be detected by the REMEDI™. With the GC-MS procedure all acid drugs of the before mentioned drug classes can only be detected in toxic concentrations. The introduction of a second extraction step using an acidic pH did not improve the sensitivity.
In conclusion, the modified GC-MS screening procedure allows a very complete detection of the antidepressants, antipsychotics, non-opioid analgesics and anticonvulsants. The disadvantage of this new procedure is a turnaround time of about 2 hours.