Pharmacogenomics Practice Questions

Q: A 57-year-old man with myocardial infarction is admitted in cardiac emergency. Which of the following drugs might cause unexpected results based on the patient's CYP2C19 genotype?

Clopidogrel. **Explanation:** The correct answer is **Clopidogrel**. **Mechanism and Genetic Link:** Clopidogrel is a **prodrug** that requires a two-step hepatic bioactivation to its active thiol metabolite. The enzyme **CYP2C19** plays a critical role in this conversion. Patients with specific genetic polymorphisms (e.g., *CYP2C19\*2* or *\*3* alleles) are "poor metabolizers." In these individuals, clopidogrel is not efficiently converted to its active form, leading to reduced platelet inhibition and an increased risk of major adverse cardiovascular events (MACE), such as stent thrombosis or recurrent MI. **Analysis of Incorrect Options:** * **Prasugrel:** While also a prodrug, its activation is more efficient and involves multiple enzymes (CYP3A4, CYP2B6). It is significantly less dependent on CYP2C19 than clopidogrel. * **Warfarin:** Its metabolism is primarily influenced by **CYP2C9** (not 2C19) and its pharmacodynamics are affected by the **VKORC1** gene. * **Ticagrelor:** This is a **direct-acting** P2Y12 inhibitor. It is not a prodrug and does not require metabolic activation; therefore, its efficacy is not affected by CYP2C19 polymorphisms. **High-Yield NEET-PG Pearls:** * **Black Box Warning:** The FDA has a boxed warning for Clopidogrel regarding its reduced effectiveness in CYP2C19 poor metabolizers. * **Drug Interaction:** **Omeprazole** (a proton pump inhibitor) inhibits CYP2C19 and can reduce the clinical efficacy of clopidogrel. If a PPI is needed, Pantoprazole is preferred as it has less inhibitory effect on CYP2C19. * **Alternative:** In known poor metabolizers, Prasugrel or Ticagrelor are the preferred antiplatelet agents.

Q: Hemolysis in glucose-6-phosphate dehydrogenase enzyme deficiency may occur with all of the following drugs except:

Penicillin. Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an X-linked recessive disorder where RBCs are unable to regenerate NADPH, making them vulnerable to oxidative stress [1]. When exposed to oxidizing agents, hemoglobin precipitates as **Heinz bodies**, leading to hemolysis. **Why Penicillin is the Correct Answer:** Penicillin is not an oxidizing agent and does not cause hemolysis in G6PD deficiency. While Penicillin can cause immune-mediated hemolytic anemia (Type II Hypersensitivity) via a hapten mechanism, it is safe to use in patients with G6PD deficiency. **Analysis of Incorrect Options:** * **Primaquine:** This is the classic "prototype" drug known to trigger severe hemolysis in G6PD-deficient individuals. It is an antimalarial that generates reactive oxygen species. * **Phenacetin:** An older NSAID/analgesic (metabolite of paracetamol) known to be a potent oxidizing agent. It is rarely used now due to nephrotoxicity and hemolytic potential. * **Probenecid:** A uricosuric agent used in gout that is documented to cause oxidative stress and hemolysis in susceptible G6PD-deficient patients. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for G6PD Triggers:** "**S**ell **A**ll **F**ava **B**eans" (**S**ulfonamides/Sulfones like Dapsone, **A**ntimalarials like Primaquine, **F**ava beans, **B**enzocaine/Nitrofurantoin). * **Diagnosis:** Peripheral smear shows **Heinz bodies** (denatured hemoglobin) and **Bite cells** (degluticytes) formed by splenic macrophages. * **Testing Tip:** Do not perform the G6PD enzyme assay during an acute hemolytic episode, as young reticulocytes have normal enzyme levels and may yield a **false-normal** result. Wait 6–8 weeks.

Q: Which drug does NOT cause hemolysis in G6PD deficiency?

Corticosteroids. **Explanation:** **G6PD deficiency** is an X-linked recessive disorder where the lack of Glucose-6-Phosphate Dehydrogenase leads to a failure in generating NADPH [2]. NADPH is essential for maintaining a pool of **reduced glutathione**, which protects red blood cells (RBCs) from oxidative damage. Without it, oxidizing agents cause hemoglobin to denature into **Heinz bodies**, leading to hemolysis. **Why Corticosteroids are the correct answer:** Corticosteroids (Option C) are anti-inflammatory and immunosuppressive agents [1]. They do not possess oxidizing properties and do not interfere with the pentose phosphate pathway or glutathione metabolism. Therefore, they do not trigger hemolytic crises in G6PD-deficient individuals. **Why the other options are incorrect:** * **Primaquine (Option A):** A classic antimalarial and the most notorious trigger for G6PD-related hemolysis. It generates reactive oxygen species (ROS) that overwhelm the RBC's limited antioxidant capacity. * **Dapsone (Option B):** Used for leprosy and dermatitis herpetiformis, this sulfonamide derivative is a potent oxidizing agent that consistently causes hemolysis in deficient patients. * **Methylene Blue (Option D):** Used to treat methemoglobinemia, it acts as an electron acceptor. In G6PD deficiency, it can actually worsen oxidative stress and is contraindicated. **NEET-PG High-Yield Pearls:** 1. **Diagnosis:** Look for "Bite cells" (degluticytes) and "Heinz bodies" (crystal violet stain) on a peripheral smear. 2. **Common Triggers:** Fava beans (Favism), Nitrofurantoin, Sulfonamides, and Infections (the most common cause). 3. **Genetics:** X-linked recessive; provides a protective advantage against *Plasmodium falciparum* malaria. 4. **Mnemonic (AAA):** Avoid **A**ntimalarials (Primaquine), **A**ntibiotics (Sulfas), and **A**spirin (high doses).

Q: Which drug does NOT cause hemolysis in a patient with G6PD deficiency?

Chloroquine. **Explanation:** Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency is an X-linked recessive disorder where RBCs lack the ability to regenerate reduced glutathione, making them highly susceptible to oxidative stress. When exposed to certain oxidizing drugs, hemoglobin precipitates into **Heinz bodies**, leading to hemolysis. **Why Chloroquine is the correct answer:** While Chloroquine is an antimalarial, it is considered **safe** in standard therapeutic doses for G6PD-deficient individuals. It does not possess significant oxidizing potential compared to other drugs in its class. In contrast, its cousin **Primaquine** is the classic prototype for drug-induced hemolysis in these patients. **Analysis of Incorrect Options:** * **Primaquine (Option A):** This is the most high-yield trigger. It is an 8-aminoquinoline that causes significant oxidative stress. G6PD testing is mandatory before prescribing Primaquine for the radical cure of *P. vivax*. * **Nalidixic Acid (Option C):** A first-generation quinolone known to trigger hemolytic anemia in G6PD-deficient patients. * **Nitrofurantoin (Option D):** Commonly used for UTIs, this drug is a well-documented oxidizing agent that must be avoided in these patients. **NEET-PG High-Yield Pearls:** * **Mnemonic for G6PD Triggers:** "**S**ell **P**ins **A**nd **N**eedles" (**S**ulfonamides, **P**rimaquine, **A**ntipyretics/Dapsone, **N**itrofurantoin/Nalidixic acid). * **Safe Antimalarials:** Chloroquine, Quinine, and Proguanil. * **Diagnosis:** Peripheral smear shows **"Bite cells"** (degmacytes) and **Heinz bodies** (denatured hemoglobin) visualized with supravital stains like Crystal Violet. * **Key Contraindication:** Rasburicase (used in Tumor Lysis Syndrome) is strictly contraindicated in G6PD deficiency.

Q: Which of the following drugs can cause hemolysis in patients with Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency?

Chloroquine. **Explanation:** **Mechanism of Action:** G6PD deficiency is an X-linked recessive disorder where erythrocytes lack the enzyme necessary to maintain levels of **reduced glutathione**. Reduced glutathione is essential for neutralizing reactive oxygen species (ROS). When patients are exposed to "oxidant drugs," ROS accumulate, leading to the denaturation of hemoglobin (forming **Heinz bodies**) and subsequent hemolysis. **Chloroquine**, an antimalarial, is a well-known oxidant drug that triggers this hemolytic process in susceptible individuals. **Analysis of Options:** * **Chloroquine (Correct):** It is a classic trigger for oxidative stress in RBCs. While its cousin, Primaquine, is a more potent trigger, Chloroquine remains a high-yield contraindication in G6PD deficiency. * **Cephalosporins & Ampicillin (Incorrect):** These are beta-lactam antibiotics. While they can rarely cause immune-mediated hemolytic anemia (Type II hypersensitivity), they do not cause oxidative hemolysis related to G6PD deficiency. * **Erythromycin (Incorrect):** This macrolide is generally safe in G6PD-deficient patients. It is more commonly associated with GI upset and cholestatic jaundice. **NEET-PG High-Yield Pearls:** * **Mnemonic for G6PD Triggers:** "**AAA**" – **A**ntimalarials (Primaquine, Chloroquine), **A**ntibiotics (Sulfonamides, Nitrofurantoin, Dapsone), and **A**ntipyretics (high-dose Aspirin). * **Peripheral Smear Findings:** Look for **Heinz Bodies** (denatured Hb) and **Bite Cells** (deformed RBCs after splenic macrophages remove Heinz bodies). * **Key Contraindication:** **Primaquine** is the most notorious trigger; always test for G6PD levels before initiating radical cure for *P. vivax*. * **Other Triggers:** Fava beans (Favism) and infections (the most common cause of hemolysis in these patients).

Q: What does X represent in the given graph?

Therapeutic window. ***Therapeutic window*** - The **therapeutic window** represents the drug concentration range between the **minimum effective concentration (MEC)** and **minimum toxic concentration (MTC)**. - This region (X) indicates the safe and effective dosing range where the drug provides **therapeutic benefit** without causing **toxicity**. *Therapeutic index* - The **therapeutic index** is a numerical ratio calculated as **TD50/ED50** (toxic dose/effective dose), not a region on a graph. - It represents the **safety margin** of a drug as a single value, not a concentration range. *Therapeutic dose* - **Therapeutic dose** refers to a specific **amount of drug administered** to achieve desired effects. - It is not represented as a region between two concentration thresholds but as a **discrete dosing amount**. *Therapeutic efficacy* - **Therapeutic efficacy** describes the **maximum response** a drug can produce regardless of dose. - It relates to drug **effectiveness** and **intrinsic activity**, not to concentration ranges between safety thresholds.

Q: A patient with history of ischemic stroke was started on clopidogrel. However, she had another attack of stroke after 6 months. Which of the following is likely to be responsible for the failure of clopidogrel in this patient?

Downregulation of CYP2C19. ***Reduced function/Loss of function of CYP2C19*** - **Clopidogrel** is a **prodrug** that requires activation by **hepatic cytochrome P450 (CYP) enzymes**, primarily **CYP2C19**, to its active metabolite. - **Genetic polymorphisms** causing **reduced function or loss of function of CYP2C19** (e.g., CYP2C19*2, *3 alleles) result in insufficient conversion of clopidogrel to its active form, leading to **clopidogrel resistance** and increased risk of thrombotic events like recurrent stroke. - These **poor metabolizers** have significantly reduced antiplatelet response to standard clopidogrel doses. *Upregulation of CYP1A1* - **CYP1A1** is involved in the metabolism of various xenobiotics but plays a **minimal role** in clopidogrel activation. - Upregulation of CYP1A1 would not be a primary factor in clopidogrel failure as it is not the main enzyme responsible for its bioactivation. *Downregulation of CYP2E1* - **CYP2E1** is primarily involved in the metabolism of small organic molecules, some drugs, and toxins, and has **no significant role** in the bioactivation of clopidogrel. - Therefore, changes in its expression would not impact clopidogrel's efficacy. *Downregulation of CYP2D6* - **CYP2D6** is a major enzyme involved in the metabolism of many psychoactive drugs, beta-blockers, and opioids, but plays only a **minor role** in clopidogrel activation compared to CYP2C19. - Downregulation of CYP2D6 would not be the primary cause of clopidogrel failure.

Q: Prolonged apnea may occur in patients with a genetically determined abnormal variant of cholinesterase following intravenous administration of

Succinylcholine or mivacurium. ***Succinylcholine or mivacurium*** - **Both succinylcholine and mivacurium** are metabolized by **plasma cholinesterase (pseudocholinesterase)**. - Patients with **atypical (abnormal) plasma cholinesterase** have reduced or absent enzyme activity, leading to **prolonged duration of action** and extended paralysis/apnea with both drugs. - **Succinylcholine** is a depolarizing neuromuscular blocker whose duration increases from 5-10 minutes to several hours in affected patients. - **Mivacurium** is the only non-depolarizing neuromuscular blocker metabolized by plasma cholinesterase; its duration increases from 15-20 minutes to several hours in these patients. - This is a classic **pharmacogenetic** condition requiring prolonged ventilatory support until the drug effect dissipates. *Succinylcholine (alone)* - While succinylcholine is affected by atypical cholinesterase, this option is incomplete as it excludes mivacurium, which is equally affected by the genetic variant. *Mivacurium (alone)* - While mivacurium is affected by atypical cholinesterase, this option is incomplete as it excludes succinylcholine, the more commonly used drug that is also affected. *Tubocurarine* - **Tubocurarine** is a non-depolarizing neuromuscular blocker that undergoes **renal excretion** and hepatic metabolism, not plasma cholinesterase degradation. - Its duration of action is **not affected** by variations in cholinesterase activity.

Q: Which enzyme deficiency is associated with severe reactions to sulfonamides in HIV patients?

Glucose-6-phosphate dehydrogenase. ***Glucose-6-phosphate dehydrogenase*** - **G6PD deficiency** is the key enzyme deficiency associated with severe hemolytic reactions to sulfonamides - G6PD is essential for protecting RBCs against **oxidative stress** by maintaining glutathione in its reduced form - Sulfonamides (especially cotrimoxazole used for PCP prophylaxis in HIV) cause **oxidative damage** leading to **acute hemolytic anemia** in G6PD-deficient patients - In **HIV patients**, this is particularly important as sulfonamides are commonly prescribed *N-acetyltransferase* - NAT enzyme is involved in Phase II metabolism of sulfonamides through acetylation - Deficiency leads to **slow acetylator phenotype** with higher drug levels - Associated with different toxicities like hypersensitivity reactions and lupus-like syndrome - Does not cause the acute hemolytic anemia characteristic of G6PD deficiency *Cytochrome P450 2D6* - CYP2D6 metabolizes codeine, tramadol, antidepressants, and antipsychotics - Plays **minimal role** in sulfonamide metabolism - Deficiency affects metabolism of its specific substrates, not sulfonamides *Glutathione S-transferase* - GST enzymes conjugate glutathione to xenobiotics for detoxification - While involved in oxidative stress protection, GST deficiency is not the primary cause of severe sulfonamide reactions - G6PD deficiency is the specific enzymatic defect causing acute hemolytic crisis with sulfonamides

Q: Best predictor of varenicline response in smoking cessation is:

CHRNA5 gene variant. ***CHRNA5 gene variant*** - Genetic variations in the **CHRNA5 gene** (part of the CHRNA5-CHRNA3-CHRNB4 gene cluster on chromosome 15q25) encode subunits of nicotinic acetylcholine receptors and influence nicotine dependence and smoking behavior. - In the context of **pharmacogenomics**, CHRNA5 variants represent the **biological/genetic predictor** of treatment response, distinguishing individual variability in varenicline efficacy. - Among the options provided, this is the only **genetic factor** that can predict differential drug response at a molecular level. *Nicotine dependence score* - While a higher **nicotine dependence score** (measured by tools like Fagerström Test) indicates greater addiction severity and may correlate with treatment outcomes, it is a **clinical assessment**, not a biological predictor. - It reflects the phenotype (observable addiction) rather than the underlying genetic mechanism affecting drug response. *Pack-years* - **Pack-years** quantify cumulative tobacco exposure (packs per day × years smoked), indicating health risk and damage burden. - This is a **historical exposure metric**, not a predictor of varenicline's pharmacological efficacy or individual response variability. *Previous quit attempts* - The number of **previous quit attempts** reflects **behavioral patterns** and motivation but does not predict how an individual's nicotinic receptors will respond to varenicline. - This is a psychosocial factor rather than a pharmacogenomic predictor of drug response.

Question 1

A 57-year-old man with myocardial infarction is admitted in cardiac emergency. Which of the following drugs might cause unexpected results based on the patient's CYP2C19 genotype?

Accepted Answer

Clopidogrel

Answer

Prasugrel

Answer

Warfarin

Answer

Ticagrelor

Question 2

Hemolysis in glucose-6-phosphate dehydrogenase enzyme deficiency may occur with all of the following drugs except:

Accepted Answer

Penicillin

Answer

Primaquine

Answer

Phenacetin

Answer

Probenecid

Question 3

Which drug does NOT cause hemolysis in G6PD deficiency?

Accepted Answer

Corticosteroids

Answer

Primaquine

Answer

Dapsone

Answer

Methylene blue

Question 4

Which drug does NOT cause hemolysis in a patient with G6PD deficiency?

Accepted Answer

Chloroquine

Answer

Primaquine

Answer

Nalidixic acid

Answer

Nitrofurantoin

Question 5

Which of the following drugs can cause hemolysis in patients with Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency?

Accepted Answer

Chloroquine

Answer

Cephalosporins

Answer

Ampicillin

Answer

Erythromycin

Question 6

What does X represent in the given graph?

Accepted Answer

Therapeutic window

Answer

Therapeutic index

Answer

Therapeutic dose

Answer

Therapeutic efficacy

Question 7

A patient with history of ischemic stroke was started on clopidogrel. However, she had another attack of stroke after 6 months. Which of the following is likely to be responsible for the failure of clopidogrel in this patient?

Accepted Answer

Downregulation of CYP2C19

Answer

Upregulation of CYP1A1

Answer

Downregulation of CYP2E1

Answer

Downregulation of CYP2D6

Question 8

Prolonged apnea may occur in patients with a genetically determined abnormal variant of cholinesterase following intravenous administration of

Accepted Answer

Succinylcholine or mivacurium

Answer

Mivacurium

Answer

Tubocurarine

Answer

Succinylcholine

Question 9

Which enzyme deficiency is associated with severe reactions to sulfonamides in HIV patients?

Accepted Answer

Glucose-6-phosphate dehydrogenase

Answer

N-acetyltransferase

Answer

Cytochrome P450 2D6

Answer

Glutathione S-transferase

Question 10

Best predictor of varenicline response in smoking cessation is:

Accepted Answer

CHRNA5 gene variant

Answer

Nicotine dependence score

Answer

Pack-years

Answer

Previous quit attempts

Pharmacogenomics — MCQs

Pharmacogenomics — MCQs

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