Clinical Pharmacology and Drug Toxicity — MCQs

Clinical Pharmacology and Drug Toxicity Indian Medical PG Practice Questions and MCQs

Question 61: Which of the following drugs is not associated with pure red cell aplasia?

A. Phenytoin
B. Isoniazid
C. Erythropoietin (Correct Answer)
D. Chloramphenicol

Explanation: **Explanation:** **Pure Red Cell Aplasia (PRCA)** is a rare hematologic syndrome characterized by a severe reduction in erythroid precursors in the bone marrow, leading to isolated anemia with normal leukocyte and platelet counts. **Why Erythropoietin is the correct answer:** In the context of standard pharmacological side effects, **Erythropoietin (EPO)** is actually used to *treat* various forms of anemia. While there is a rare clinical phenomenon where patients develop "Anti-EPO antibody-mediated PRCA" (typically associated with specific formulations like Eprex), it is considered an **idiosyncratic immune reaction** rather than a direct toxic effect of the drug itself. In most standardized examinations, Erythropoietin is categorized as a therapeutic agent for anemia, whereas the other options are classic causes of drug-induced bone marrow suppression or PRCA. **Analysis of Incorrect Options:** * **Phenytoin:** This antiepileptic is a well-documented cause of drug-induced PRCA and megaloblastic anemia (due to folate interference). * **Isoniazid (INH):** A primary anti-tubercular drug known to cause PRCA, likely through direct toxicity to erythroid progenitor cells. * **Chloramphenicol:** While most famous for causing **Aplastic Anemia** (pancytopenia), it can also manifest as isolated PRCA or dose-dependent reversible marrow suppression. **High-Yield Clinical Pearls for NEET-PG:** * **Most common viral cause of PRCA:** Parvovirus B19 (targets pro-erythroblasts). * **Most common tumor associated with PRCA:** Thymoma (reverses after thymectomy in 30% of cases). * **Diamond-Blackfan Anemia:** A congenital form of PRCA presenting in infancy. * **Key distinction:** Unlike Aplastic Anemia, PRCA shows **normal** WBC and Platelet counts.

Question 62: Which of the following drugs is implicated in causing urinary retention?

A. Lisinopril
B. Meperidine (Correct Answer)
C. Terazosin
D. Losartan

Explanation: **Explanation:** **Correct Option: B. Meperidine** Meperidine (Pethidine) is a synthetic opioid analgesic. While most opioids can cause urinary retention by increasing the tone of the bladder sphincter and decreasing the detrusor muscle's excitability, Meperidine has a distinct pharmacological profile. It possesses significant **anticholinergic (atropine-like) properties**. Anticholinergic drugs inhibit the parasympathetic nervous system, leading to relaxation of the detrusor muscle and contraction of the internal urethral sphincter, which directly results in acute urinary retention. **Incorrect Options:** * **A & D (Lisinopril & Losartan):** Lisinopril (an ACE inhibitor) and Losartan (an ARB) primarily affect the Renin-Angiotensin-Aldosterone System (RAAS). Their main side effects include hyperkalemia and renal impairment, but they do not typically cause urinary retention. * **C (Terazosin):** This is an **alpha-1 blocker**. It is actually used to *treat* urinary retention associated with Benign Prostatic Hyperplasia (BPH) by relaxing the smooth muscles of the bladder neck and prostate. **High-Yield NEET-PG Pearls:** * **Meperidine Metabolism:** It is metabolized to **normeperidine**, which is neurotoxic and can cause tremors, myoclonus, and **seizures** (especially in renal failure). * **Mydriasis:** Unlike most opioids that cause miosis (pinpoint pupils), Meperidine can cause mydriasis due to its anticholinergic effect. * **Drug Interaction:** Meperidine is contraindicated with **MAO inhibitors** as it can precipitate a life-threatening **Serotonin Syndrome**. * **Other drugs causing retention:** Tricyclic antidepressants (TCAs), first-generation antihistamines, and antiparkinsonian drugs (due to anticholinergic effects).

Question 63: Which drug is likely to cause livedo reticularis?

A. Gabapentin
B. Amantadine (Correct Answer)
C. Pramipexole
D. Levodopa

Explanation: **Explanation:** **Amantadine** is a tricyclic amine used in the management of Parkinson’s disease and formerly as an antiviral. The classic dermatological side effect associated with Amantadine is **Livedo Reticularis**. **Mechanism of Action for Side Effect:** Livedo reticularis is a purplish, net-like (reticulated) vascular pattern on the skin, most commonly seen on the lower extremities. It occurs because Amantadine causes the release of catecholamines from peripheral nerve terminals, leading to localized **vasoconstriction** of dermal arterioles and subsequent venous congestion. This reaction is usually benign and reversible upon discontinuation of the drug. **Analysis of Incorrect Options:** * **Gabapentin (A):** Primarily used for neuropathic pain and focal seizures. Common side effects include sedation, dizziness, and peripheral edema, but it does not cause livedo reticularis. * **Pramipexole (C):** A non-ergot dopamine agonist. Its characteristic side effects include sleep attacks (sudden onset of sleep), impulse control disorders (pathological gambling), and pedal edema. * **Levodopa (D):** The precursor to dopamine. Common side effects include nausea, orthostatic hypotension, dyskinesias, and "on-off" phenomena. It is not associated with livedo reticularis. **NEET-PG High-Yield Pearls:** * **Amantadine Triple Threat:** Remember its three distinct uses/features: 1. Anti-Parkinsonian (increases dopamine release), 2. Antiviral (Influenza A - M2 ion channel blocker), 3. Treatment for Levodopa-induced dyskinesia (NMDA receptor antagonism). * **Other Side Effects:** Apart from livedo reticularis, Amantadine can cause ankle edema and anticholinergic-like effects (dry mouth, blurred vision). * **Differential Diagnosis:** Livedo reticularis can also be a clinical sign of systemic conditions like Polyarteritis Nodosa (PAN) or Systemic Lupus Erythematosus (SLE).

Question 64: A patient on anti-psychotic drugs develops a temperature of 104°F, a blood pressure of approximately 150/100 mmHg, and abnormal behavior. What is the likely diagnosis?

A. Aggravation of psychosis
B. Parkinsonism
C. Dystonia
D. Neuroleptic malignant syndrome (Correct Answer)

Explanation: ### Explanation The patient is presenting with the classic triad of **Neuroleptic Malignant Syndrome (NMS)**: hyperpyrexia (104°F), autonomic instability (hypertension), and altered mental status (abnormal behavior), occurring in the context of antipsychotic use. **1. Why Neuroleptic Malignant Syndrome (NMS) is correct:** NMS is a life-threatening idiosyncratic reaction to dopamine antagonists (typically high-potency typical antipsychotics like Haloperidol). The underlying mechanism involves **severe dopamine (D2) blockade** in the nigrostriatal pathway (leading to "lead-pipe" rigidity) and the hypothalamus (causing impaired thermoregulation and hyperpyrexia). Autonomic dysfunction leads to fluctuating blood pressure and tachycardia. **2. Why other options are incorrect:** * **Aggravation of psychosis:** While abnormal behavior occurs, psychosis alone does not cause high-grade fever or significant autonomic instability. * **Parkinsonism:** This is an Extrapyramidal Side Effect (EPS) characterized by tremors, bradykinesia, and rigidity, but it lacks the systemic toxicity (fever/autonomic collapse) seen here. * **Dystonia:** This involves acute, painful muscle spasms (e.g., torticollis, oculogyric crisis) usually occurring within hours of drug administration, without systemic symptoms. **3. NEET-PG High-Yield Pearls:** * **Clinical Marker:** Elevated **Creatine Kinase (CK)** levels due to intense muscle rigidity. * **Treatment of Choice:** Immediate drug withdrawal + Supportive care + **Dantrolene** (muscle relaxant) or **Bromocriptine** (D2 agonist). * **Differential Diagnosis:** Differentiate from *Serotonin Syndrome* (which presents with hyperreflexia and myoclonus) and *Malignant Hyperthermia* (triggered by inhalational anesthetics/succinylcholine). * **Mnemonic (FEVER):** **F**ever, **E**ncephalopathy, **V**itals unstable, **E**levated enzymes (CK), **R**igidity.

Question 65: A 40-year-old male patient presents with abdominal pain and vomiting following exposure to arsenic and cadmium. Which detoxifying agent is indicated for this patient?

A. Desferrioxamine
B. British antilewisite (Correct Answer)
C. Deferiprone
D. D-Penicillamine

Explanation: ### Explanation The correct answer is **British antilewisite (BAL)**, also known as **Dimercaprol**. **1. Why British antilewisite (BAL) is correct:** BAL is a chelating agent containing two sulfhydryl (-SH) groups. It works by forming stable, non-toxic, heterocyclic ring complexes with heavy metals, which are then excreted in the urine. It is the drug of choice for acute poisoning with **Arsenic, Mercury (inorganic), and Antimony**. It is also used as an adjuvant to EDTA in **Lead poisoning**. Its ability to compete with endogenous sulfhydryl groups in enzymes makes it effective against the multi-organ toxicity caused by arsenic and cadmium. **2. Why the other options are incorrect:** * **Desferrioxamine (Option A):** This is a specific chelating agent used for **Acute Iron poisoning** and chronic iron overload (hemosiderosis). It has no role in heavy metal poisoning like arsenic. * **Deferiprone (Option C):** This is an orally active iron chelator primarily used for **Thalassemia major** patients with iron overload. * **D-Penicillamine (Option D):** While it is a chelator, it is the drug of choice for **Wilson’s disease (Copper poisoning)** and is also used in cystinuria and rheumatoid arthritis. It is not the primary choice for acute arsenic or cadmium toxicity. **Clinical Pearls for NEET-PG:** * **BAL Administration:** It must be administered via **deep intramuscular (IM)** injection because it is dispensed in peanut oil (contraindicated in patients with peanut allergies). * **Cadmium Toxicity:** While BAL can be used, **Calcium disodium EDTA** is often preferred for chronic cadmium exposure; however, in the context of combined arsenic/cadmium exposure, BAL remains a standard answer. * **Succimer (DMSA):** This is a water-soluble analog of BAL that can be given orally and has a better safety profile. * **Arsenic Classic Sign:** Look for "Raindrop pigmentation" of the skin and "Mees' lines" on nails in chronic cases.

Question 66: Low molecular weight dextran is contraindicated in which of the following conditions?

A. Fetal distress syndrome
B. Cerebrovascular accident
C. Electrical burns
D. Thrombocytopenia (Correct Answer)

Explanation: **Explanation:** **Low Molecular Weight Dextran (Dextran-40)** is a plasma volume expander used to improve microcirculation. However, it is strictly contraindicated in **Thrombocytopenia** and other bleeding disorders. **Why Thrombocytopenia is the correct answer:** Dextran-40 exerts a potent anti-platelet effect. It coats the surface of platelets and vascular endothelium, reducing platelet adhesiveness and interfering with the function of **von Willebrand Factor (vWF)** and Factor VIII. In a patient with a low platelet count (thrombocytopenia), this further impairment of primary hemostasis significantly increases the risk of life-threatening hemorrhage. Additionally, it can induce "Dextran-induced nephrosis," which is exacerbated in dehydrated states. **Analysis of Incorrect Options:** * **Fetal Distress Syndrome:** Dextran is not contraindicated here; in fact, volume expanders may be used in maternal resuscitation to improve placental perfusion. * **Cerebrovascular Accident (CVA):** Dextran-40 is often used in ischemic stroke to decrease blood viscosity and improve cerebral blood flow (rheological effect), though its routine use is now debated. * **Electrical Burns:** Fluid resuscitation is the mainstay of burn management. While crystalloids are preferred (Parkland formula), dextrans are not specifically contraindicated unless there is associated acute kidney injury or active bleeding. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Reduces blood viscosity and prevents "sludging" of RBCs. * **Adverse Effects:** Anaphylaxis (most common serious reaction), prolonged bleeding time, and acute renal failure. * **Interference:** Dextran can interfere with blood grouping and cross-matching; therefore, blood samples should be drawn *before* administration. * **Contraindications:** Severe CHF, Renal failure, Thrombocytopenia, and Hypofibrinogenemia.

Question 67: All of the following drugs cause hemolysis in G-6 PD deficiency except?

A. Primaquine
B. Nitrofurantoin
C. Sulfonamide
D. Erythromycin (Correct Answer)

Explanation: **Explanation:** **Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency** is an X-linked recessive disorder where red blood cells (RBCs) lack the enzyme necessary to maintain levels of reduced glutathione. Without glutathione, RBCs cannot neutralize reactive oxygen species, leading to hemoglobin oxidation (Heinz bodies) and subsequent hemolysis when exposed to oxidative stress. **Why Erythromycin is the correct answer:** Erythromycin is a macrolide antibiotic that does not possess oxidative properties. It is considered safe to use in patients with G6PD deficiency. It does not interfere with the redox cycle of the RBC, thus it does not trigger hemolytic anemia. **Analysis of incorrect options (Oxidative triggers):** * **Primaquine:** This is the classic "high-risk" drug. As an antimalarial, it induces significant oxidative stress and is the most common pharmacological cause of hemolysis in G6PD-deficient individuals. * **Nitrofurantoin:** Frequently used for UTIs, this drug is a potent oxidizing agent and is strictly contraindicated in G6PD deficiency. * **Sulfonamides (e.g., Sulfamethoxazole):** These drugs increase the production of free radicals, which overwhelm the limited antioxidant capacity of G6PD-deficient cells. **NEET-PG High-Yield Pearls:** * **Mnemonic for G6PD triggers:** "**S**ell **P**ainful **A**ntimalarials **N**ow" (**S**ulfonamides, **P**rimaquine, **A**spirin/Dapsone, **N**itrofurantoin). * **Diagnosis:** Look for **"Bite cells"** (degmacytes) and **"Heinz bodies"** (denatured hemoglobin) on a peripheral smear. * **Fava Beans:** Ingestion causes "Favism," a severe hemolytic reaction in certain G6PD variants (Mediterranean type). * **Other notable triggers:** Dapsone, Rasburicase, and Methylene blue.

Question 68: What is Cerliponase alpha?

A. Recombinant tripeptidyl peptidase 1 (TPP-1) (Correct Answer)
B. Recombinant beta-glucuronidase
C. NMDA receptor blocker
D. GLP analogue

Explanation: **Explanation:** **Cerliponase alfa** is a hydrolytic lysosomal exopeptidase. It is the first FDA-approved enzyme replacement therapy (ERT) for **Neuronal Ceroid Lipofuscinosis Type 2 (CLN2)**, also known as Late Infantile Batten Disease. 1. **Why Option A is Correct:** CLN2 is an autosomal recessive neurodegenerative disorder caused by a deficiency in the enzyme **tripeptidyl peptidase 1 (TPP-1)**. This deficiency leads to the accumulation of storage materials (lipofuscins) in lysosomes, causing progressive neurodegeneration. Cerliponase alfa is a **recombinant human TPP-1** that is administered via intraventricular infusion to bypass the blood-brain barrier and restore enzymatic activity in the CNS. 2. **Why Other Options are Incorrect:** * **Option B (Recombinant beta-glucuronidase):** This refers to **Vestronidase alfa**, used for treating Mucopolysaccharidosis type VII (Sly syndrome). * **Option C (NMDA receptor blocker):** Drugs like Memantine or Ketamine act via this mechanism. They are not enzyme replacement therapies. * **Option D (GLP-1 analogue):** Drugs like Liraglutide or Semaglutide are GLP-1 analogues used in Diabetes Mellitus and obesity management. **High-Yield Clinical Pearls for NEET-PG:** * **Route of Administration:** It is unique because it is administered via an **intracerebroventricular (ICV)** device (Ommaya reservoir) to ensure it reaches the brain. * **Indication:** Specifically for CLN2 to slow the loss of ambulation (walking ability) in symptomatic pediatric patients. * **Naming Convention:** The suffix **"-ase"** denotes an enzyme, and **"alfa"** typically refers to the first recombinant version of that protein.

Question 69: Which of the following drugs can produce urinary retention?

A. Alcohol
B. Captopril
C. Cinnarizine (Correct Answer)
D. All of the above

Explanation: **Explanation:** The correct answer is **Cinnarizine**. **1. Why Cinnarizine is correct:** Cinnarizine is a piperazine derivative primarily used as an H1-receptor antagonist (antihistamine) for motion sickness and vertigo. Like many first-generation antihistamines, it possesses significant **anticholinergic (antimuscarinic) properties**. By blocking M3 muscarinic receptors on the detrusor muscle of the bladder, it prevents contraction, leading to **urinary retention**. This is a critical side effect to monitor, especially in elderly male patients with pre-existing Benign Prostatic Hyperplasia (BPH). **2. Why the other options are incorrect:** * **Alcohol:** Alcohol acts as a diuretic. It inhibits the release of Antidiuretic Hormone (ADH/Vasopressin) from the posterior pituitary, leading to increased free water clearance and **polyuria** (increased urination), rather than retention. * **Captopril:** This is an ACE inhibitor. Its primary side effects include dry cough (due to bradykinin accumulation), hyperkalemia, and angioedema. It does not possess anticholinergic activity and does not cause urinary retention. **Clinical Pearls for NEET-PG:** * **Anticholinergic Toxidrome:** Remember the mnemonic "Red as a beet, dry as a bone, blind as a bat, mad as a hatter, and **full as a flask**" (referring to urinary retention). * **Drugs causing urinary retention:** Tricyclic antidepressants (Amitriptyline), Atropine, first-generation antihistamines (Diphenhydramine, Promethazine), and Antiparkinsonian drugs (Benzhexol/Trihexyphenidyl). * **Cinnarizine specific:** It also has Calcium Channel Blocking activity, which contributes to its use in peripheral vascular disorders and labyrinthine disturbances.

Question 70: A patient on nitroprusside therapy developed cyanide toxicity. Sodium nitrite was administered intravenously to combat this poisoning. The beneficial effect of sodium nitrite in this case is dependent on which of the following mechanisms?

A. Direct chelation of cyanide with sodium nitrite
B. Vasodilation caused by sodium nitrite
C. Conversion of hemoglobin to methemoglobin by sodium nitrite (Correct Answer)
D. Facilitation of cyanocobalamin formation by sodium nitrite

Explanation: ### Explanation **Mechanism of Action (Why Option C is Correct):** Cyanide toxicity occurs because cyanide ($CN^-$) binds with high affinity to the ferric iron ($Fe^{3+}$) in **cytochrome oxidase**, inhibiting the mitochondrial electron transport chain and causing cellular hypoxia. Sodium nitrite works by oxidizing the ferrous iron ($Fe^{2+}$) in hemoglobin to ferric iron ($Fe^{3+}$), creating **methemoglobin**. Cyanide has a higher affinity for the ferric iron in methemoglobin than for the ferric iron in cytochrome oxidase. Consequently, methemoglobin "sequesters" cyanide from the mitochondria to form **cyanmethemoglobin**, thereby restoring cellular respiration. **Analysis of Incorrect Options:** * **Option A:** Sodium nitrite does not directly chelate cyanide. Chelation is the mechanism for **Dicobalt edetate** or **Hydroxocobalamin**. * **Option B:** While nitrites are potent vasodilators (which can actually cause dose-limiting hypotension), this is a side effect in this context, not the therapeutic mechanism for treating poisoning. * **Option C:** Sodium nitrite does not form cyanocobalamin; **Hydroxocobalamin** (Vitamin $B_{12a}$) combines with cyanide to form cyanocobalamin ($B_{12}$), which is then excreted by the kidneys. **High-Yield NEET-PG Pearls:** 1. **The Standard Cyanide Antidote Kit (CAK):** Consists of three steps: * **Amyl Nitrite** (Inhaled): Immediate action while IV access is secured. * **Sodium Nitrite** (IV): Induces methemoglobinemia. * **Sodium Thiosulfate** (IV): Provides a sulfur donor for the enzyme **rhodanase**, which converts cyanmethemoglobin into non-toxic **thiocyanate** for renal excretion. 2. **Drug of Choice:** **Hydroxocobalamin** is now preferred over nitrites because it does not reduce the oxygen-carrying capacity of blood (nitrites turn hemoglobin into methemoglobin, which cannot carry $O_2$). 3. **Nitroprusside Toxicity:** Risk increases with high doses, prolonged infusion, or renal/hepatic failure. It presents with metabolic acidosis and "cherry-red" venous blood.

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