Conclusion

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The page below is a sample from the LabCE course Drug Metabolism. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Conclusion

Drugs metabolized primarily to glucuronic acid conjugates by UDP-glucuronyl transferase show negligible potential for drug-to-drug interactions caused by enzyme induction or inhibition.
Most laboratories do not test for glucuronides. Instead, they convert them back to the drug's free form by performing acid, alkaline, or enzyme hydrolysis on the urine specimen before extraction and analysis by GC/MS or LC/MS.
Drugs metabolized primarily by UDP-glucuronyl transferase:
  • THC-COOH
  • Morphine
  • Hydromorphone
  • Oxymorphone
Drugs metabolized primarily by CYP enzymes can produce unexpected and confusing results in drug tests. Patients taking medications or substances that interact with the drug being tested for by inhibiting the CYP enzymes involved or patients that are poor metabolizers of the enzyme will have elevated levels of the parent drug in their urine and lower metabolites. Conversely, patients taking medications or substances that interact with the drug being tested for by inducing the CYP enzymes involved or patients that are rapid metabolizers of the enzyme will have elevated levels of metabolites in their urine and lower levels of parent drug than usually seen. Patients who have a genetic polymorphism in combination with taking an interacting drug can have urine drug test results that are very confusing. More importantly, these patients can experience very high toxicity.