Glucuronides in Pain Management
Norman Roberts of Liverpool University Hospital asked me the following question concerning the use of Disposible Pipette Extraction for the measurement of pain management drugs in urine, having just read a copy of a poster on the topic:
I am just wondering why urines were hydrolysed as we dilute and then direct inject to the MS. This is because we can see the morph 3 and 6 glucuronides as well as codeine gluc. These are very important metabolites in pain management!
I didn’t know the answer to that one and Bill Brewer of DPX laboratories (who produced the poster) kindly provided the answer:
I have been working with several pain management labs recently, and it seems that each laboratory uses a different protocol regarding hydrolysis. Some laboratories choose to perform the hydrolysis step in order to determine a total concentration of morphine, codeine, etc. These labs seem to be the larger and more established ones, probably labs that have traditionally used GC/MS for opiate analysis.
There are also laboratories that do not hydrolyze samples for the mere reason of getting higher throughput–these labs do not target the glucuronide conjugates at all. They perform a “dilute and shoot” and simply target the parent compounds. In my opinion, these labs are more focused on the business side of pain management testing than the quality of the results. These labs will not likely get consistent results with other clinical labs. This could be a problem, depending on how their results are interpreted. They will certainly get false negative results for many benzos.
In your case, there is nothing wrong with analyzing the parent compounds and the glucuronides. I actually think this would be preferred, but the only problem would be dealing with the additional costs of maintaining glucuronide standards. Do you also maintain deuterated internal standards for glucuronide conjugated metabolites? I personally don’t know if this is necessary or if these standards even exist.
Do you analyze the glucuronide conjugates for benzos? I have found that the analysis of benzos seem to be even more problematic when it comes to hydrolysis–oftentimes the parent metabolites (not conjugated) are not even detected.
It is really more of a preference for the laboratory. Our method was set up to use the hydrolysis because we have found that most established labs performed hydrolysis–no other reason. I have not tried to analyze the glucuronides directly using our method, but this is definitely worth exploring.