CPxP Practice Test

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CPxP Practice Test (V1)

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Question 1

A patient who recently had a stent placed is prescribed clopidogrel. A pharmacogenomic test reveals the patient has a CYP2C19 *1/*2 genotype. What is the correct interpretation of this result and the appropriate therapeutic recommendation?

  1. Normal metabolizer; continue clopidogrel at the standard dose.
  2. Intermediate metabolizer; consider an alternative antiplatelet agent like prasugrel or ticagrelor.
  3. Poor metabolizer; the dose of clopidogrel should be doubled to ensure efficacy.
  4. Ultrarapid metabolizer; the patient is at an increased risk of bleeding with clopidogrel.

Question 2

A patient with acute lymphoblastic leukemia is scheduled to start therapy with mercaptopurine. Pre-treatment genetic testing shows the patient is homozygous for a low-activity TPMT allele (e.g., *3A/*3A). What is the pharmacist's responsibility based on this result?

  1. Recommend starting mercaptopurine at the standard dose with weekly monitoring of TPMT activity.
  2. Advise the provider that mercaptopurine is contraindicated in this patient.
  3. Recommend starting at a drastically reduced dose (e.g., reduced by ~90%) and frequency (e.g., three times a week) with close hematologic monitoring.
  4. Inform the provider that this genotype only affects the metabolism of azathioprine, not mercaptopurine.

Question 3

A patient of Southeast Asian descent is being started on carbamazepine for a new seizure diagnosis. Which of the following pharmacogenomic tests is considered standard of care to perform before initiating therapy in this patient?

  1. CYP2D6, to check for metabolic rate.
  2. HLA-B*15:02, to screen for risk of Stevens-Johnson Syndrome (SJS).
  3. VKORC1, to determine the patient's sensitivity to the drug.
  4. SLCO1B1, to assess for risk of carbamazepine-induced myopathy.

Question 4

According to the Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines, a patient who is a CYP2D6 ultrarapid metabolizer is prescribed codeine for pain. What is the primary safety concern?

  1. The patient will experience little to no pain relief due to rapid clearance of codeine.
  2. The patient will rapidly convert codeine to morphine, leading to an increased risk of opioid toxicity and respiratory depression.
  3. The patient is at high risk for developing a severe rash and hypersensitivity reaction.
  4. The patient will experience severe gastrointestinal side effects, such as nausea and vomiting.

Answer Key

  • Question 1: B. Intermediate metabolizer; consider an alternative antiplatelet agent like prasugrel or ticagrelor. (The *2 allele is a loss-of-function allele. As an intermediate metabolizer, the patient has reduced conversion of clopidogrel to its active form, increasing the risk of stent thrombosis. CPIC guidelines recommend an alternative.)
  • Question 2: C. Recommend starting at a drastically reduced dose (e.g., reduced by ~90%) and frequency (e.g., three times a week) with close hematologic monitoring. (TPMT poor metabolizers are at extremely high risk of life-threatening myelosuppression and require a significant dose reduction.)
  • Question 3: B. HLA-B*15:02, to screen for risk of Stevens-Johnson Syndrome (SJS). (The presence of this allele in certain Asian populations is strongly associated with carbamazepine-induced SJS/TEN, and the FDA recommends screening.)
  • Question 4: B. The patient will rapidly convert codeine to morphine, leading to an increased risk of opioid toxicity and respiratory depression. (Codeine is a prodrug converted to morphine by CYP2D6. Ultrarapid metabolizers can develop dangerously high morphine levels even at standard codeine doses.)