Drug Metabolism

Author: Robert E. Moore, MLS(ASCP)CMSCCM, TC(NRCC)
Reviewers: Kevin F. Foley PhD, MT, DABCC and Laurie Bjerklie, MA, MLS(ASCP)CM
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Continuing Education Credits

P.A.C.E.® Contact Hours: 2 hour(s)

Florida Board of Clinical Laboratory Science CE Credit Hours

Florida Board of Clinical Laboratory Science CE - General (Clinical Chemistry/UA/Toxicology): 2 hour(s)

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This is an advanced course, intended to present and discuss drug metabolism of the major drugs of abuse and its Importance in the interpretation of drug test results in the clinical laboratory. Topics include the effects of phase I and phase II metabolic reactions, the body's elimination of drugs and drug metabolites, and the various factors that affect drug metabolism.

Objectives

  • Define drug metabolism.
  • Discuss the effects of phase I and phase II metabolic reactions on the drug molecule in the context of the enzymes that mediate them.
  • Describe the role that cytochrome P450 enzymes play in phase I metabolism.
  • Identify the CYP enzymes that are polymorphic and how these polymorphisms affect metabolism in some individuals.
  • Review enzyme inhibition and enzyme induction in the context of active or inactive parent or metabolite.
  • Summarize the metabolism of the major drugs of abuse.

Course Outline

  • Metabolism
    • Drug Metabolism: Conversion of Parent Drug to Metabolites
  • Phase I Metabolic Reactions
    • Phase I Reactions: Hydrolysis, Reduction, and Oxidation
    • Which of the following statements is true concerning oxidative reactions?
    • Cytochrome P450
    • Cytochrome P450, continued
    • Polymorphisms
    • Polymorphisms, continued
    • Polymorphisms: Prodrugs
    • Enzyme Induction
    • Enzyme Induction, continued
    • Enzyme Inhibition
    • Enzyme Inhibition, continued
    • CYP2D6 is:
    • A patient taking a calcium channel blocker for high blood pressure has not experienced a significant improvement in blood pressure control. What could be the reason for this?
    • A patient is taking carbamazepine, a strong inducer of CYP3A4, for seizures. Their physician has prescribed cyclosporine to prevent rejection after a recent liver transplant. Which of the following may result?
    • First-Pass Hepatic Metabolism
    • A drug administered orally undergoes first-pass metabolism in the liver and demonstrates 32% bioavailability. The drug is available in the following dosages per tablet. Which tablet, given orally, would achieve the same effect as a 50 mg intravenous dose?
  • Phase II Metabolic Reactions
    • Phase II Metabolic Reactions
    • Conjugation
    • Which of the following statements is false concerning metabolic reactions?
    • The metabolism of morphine to morphine-6-glucuronide:
  • Elimination of Drugs and Drug Metabolites
    • Elimination of Weak Acid and Weak Base Drugs
    • Elimination, continued
    • Which of the following scenarios would increase the distribution of a drug in the body and thus give a longer window of detection in the urine?
  • Factors Affecting Drug Metabolism
    • Factors Affecting Drug Metabolism
    • Genetics
    • Age Factors
    • Age Factors, continued
    • Diet
    • Hepatic Impairment
    • Renal Impairment
    • Weight and Gender
    • Which of the following could potentially show an accumulation of a drug that is metabolized by CYP2D6?
    • Which statement is true for a newborn baby?
  • Drug Metabolism and Importance in the Interpretation of Drug Tests in the Clinical Laboratory
    • Drug Metabolism and Importance in the Interpretation of Drug Tests in the Clinical Toxicology Laboratory
    • If a drug has a half-life of 12 hours, how long will it take for the concentration of the drug in the urine to reach negligible levels?
    • Amphetamine
    • Methamphetamine
    • Methamphetamine is detected in a urine drug confirmation at 205 ng/mL and amphetamine at 830 ng/mL. Which of the following is the best interpretation of these results?
    • MDMA
    • Cocaine
    • Why is benzoylecgonine measured in routine drug screens instead of the parent compound, cocaine?
    • Marijuana
    • To determine if a car accident was due to impairment, a urine specimen was sent to a laboratory that can differentiate THC-OH and THC-COOH. THC-OH was negative, and THC-COOH was positive. Which is the most appropriate conclusion?
    • Opiates: 6-AM
    • Opiates: Codeine
    • Opiates: Morphine
    • Opiates: Hydrocodone
    • Opiates: Hydromorphone
    • Opiates: Oxycodone
    • Opiates: Oxymorphone
    • A urine sample screens positive for opiates (cutoff = 300 ng/mL) and positive for oxycodone (cutoff = 100 ng/mL). The confirmation yields a positive result for oxymorphone only. Which is the most likely explanation for the screen results?
    • A pain management patient has been prescribed oxycodone. The most recent drug test shows oxycodone at 9,815 ng/mL and oxymorphone below the cutoff. Oxymorphone is a metabolite of oxycodone and is generally detected at about 1/6th the concentration of oxycodone. What is a possible reason for not detecting oxymorphone?
    • A patient has a prescription for morphine and oxymorphone. Which of the following opiates would you expect to be confirmed?
    • A patient’s opiate confirmation yields the following results:Morphine = 13,689 ng/mLHydromorphone = 56 ng/mLCodeine = 98 ng/mLHow would you explain these results?
  • Conclusion
    • Conclusion
    • Conclusion, continued
  • References
    • References

Additional Information

Level of Instruction: Advanced
Intended Audience: Medical laboratory scientists, medical laboratory technicians, laboratory supervisors, and laboratory managers. This course is also appropriate for MLS and MLT students and pathology residents.
Author Information: Robert E. Moore, MLS(ASCP)CMSCCM, TC(NRCC), is the lead technologist in the toxicology laboratory at Kaiser Permanente in Portland, Oregon. His responsibilities include methods development and validation, review of QC data, instrument troubleshooting, and employee training/competency assessment. As a medical laboratory scientist, he has been a chemistry supervisor, toxicology supervisor, and laboratory director. He holds a bachelor's degree in Biology from Marshall University. 
The author has no conflict of interest to disclose.
Reviewer Information:
Kevin F. Foley, PhD, DABCC, MT, SC, is the director of clinical pathology for the Kaiser Permanente Northwest region. He also teaches clinical chemistry at Oregon Health Sciences University. Dr. Foley earned his PhD in clinical pharmacology and toxicology at East Carolina School of Medicine in North Carolina. He received a PhD in clinical pharmacology and toxicology from Brody School of Medicine, Greenville, NC. He has worked in laboratory medicine for over 15 years, starting his career as a medical technologist. 
Laurie Bjerklie, MA, MLS(ASCP)CM, is a Lead Education Developer. She earned a B.S. in Medical Laboratory Science from the University of North Dakota and an M.A. in Curriculum and Instruction from Saint Xavier University. She has over 15 years of experience in higher education and has held program director and faculty positions in both MLT and MLS programs.