Clinical Pharmacology and Drug Toxicity Practice Questions

Q: Which of the following drugs can result in cyanide poisoning?

Sodium Nitroprusside. **Sodium Nitroprusside (SNP)** is a potent, rapid-acting vasodilator used in hypertensive emergencies. Its chemical structure contains five cyanide groups per molecule. When administered intravenously, SNP reacts with hemoglobin to release nitric oxide (causing vasodilation) and **cyanide ions**. Under normal conditions, the liver detoxifies cyanide into thiocyanate; however, prolonged infusion or high doses can overwhelm this system, leading to **cyanide toxicity**. This manifests as metabolic acidosis, cherry-red skin, and altered mental status. **Explanation of Incorrect Options:** * **B. Amyl Nitrite:** This is actually an **antidote** for cyanide poisoning. It induces methemoglobinemia; methemoglobin has a high affinity for cyanide, pulling it away from cytochrome oxidase to form cyanmethemoglobin. * **C. Hydroxycobalamin:** This is the **preferred first-line antidote** for cyanide poisoning. It combines with cyanide to form non-toxic Vitamin B12 (cyanocobalamin), which is excreted by the kidneys. * **D. Sodium Thiosulphate:** This is a component of the standard cyanide antidote kit. It acts as a sulfur donor for the enzyme **rhodanase**, which converts toxic cyanide into less toxic thiocyanate. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism of SNP:** Increases cGMP via nitric oxide release, relaxing both arterioles and venules (decreases both Preload and Afterload). * **Cyanide Toxicity Sign:** An unexplained drop in oxygen saturation or a "narrowing of the venous-arterial $PO_2$ gradient" despite adequate ventilation. * **Management:** If SNP causes toxicity, the immediate step is to stop the infusion and administer Hydroxycobalamin or the Nitrite-Thiosulphate regimen. * **Thiocyanate Toxicity:** Long-term SNP use can also cause thiocyanate accumulation (especially in renal failure), leading to psychosis and seizures.

Q: Hemodialysis is useful in treating poisoning with all of the following agents, EXCEPT:

Nifedipine. To determine if a toxin is dialyzable, it must possess specific pharmacokinetic properties: **low molecular weight, low volume of distribution (Vd 90%)**. Hemodialysis only removes toxins present in the plasma compartment; since Nifedipine is sequestered in tissues and bound to proteins, dialysis is ineffective. Management of CCB overdose focuses on intravenous calcium, glucagon, and high-dose insulin euglycemic therapy (HIET). ### **Why the Other Options are Wrong** * **A. Salicylate (Aspirin):** Salicylates have a low Vd and are easily cleared by dialysis. Hemodialysis is the treatment of choice in severe toxicity (levels >100 mg/dL) or when there is altered mental status and renal failure [1]. * **B. Barbiturates:** Long-acting barbiturates (like Phenobarbital) have low protein binding and low Vd, making them highly amenable to removal via hemodialysis or hemoperfusion. * **C. Methanol:** Methanol is a small, water-soluble molecule with a very low Vd. Dialysis is life-saving as it removes both the parent alcohol and its toxic metabolite (formic acid), while also correcting the associated metabolic acidosis. ### **High-Yield Clinical Pearls for NEET-PG** * **Mnemonic for Dialyzable Toxins (I STUMBLE):** **I**sopropanol, **S**alicylates, **T**heophylline, **U**remia, **M**ethanol, **B**arbiturates (long-acting), **L**ithium, **E**thylene glycol [1]. * **Toxins NOT dialyzable:** Digoxin, Benzodiazepines, Tricyclic Antidepressants (TCAs), and Calcium Channel Blockers (due to high Vd or high protein binding). * **Charcoal Hemoperfusion** is generally superior to hemodialysis for **Theophylline** and **Carbamazepine** poisoning.

Q: Which of the following is NOT included in the treatment of digoxin overdose?

Hemodialysis. **Explanation:** The correct answer is **D. Hemodialysis**. **Why Hemodialysis is NOT used:** Digoxin has a very **large volume of distribution (Vd ≈ 5–7 L/kg)** because it binds extensively to skeletal muscle tissues. It also has a high molecular weight. Because most of the drug is sequestered in the tissues rather than the plasma, extracorporeal removal methods like hemodialysis, peritoneal dialysis, and hemoperfusion are **ineffective** in clearing digoxin from the body. **Analysis of Incorrect Options:** * **A. Potassium:** Digoxin inhibits the Na+/K+ ATPase pump, competing with potassium. Hypokalemia exacerbates digoxin toxicity. If potassium levels are low or normal, cautious potassium supplementation is indicated to displace digoxin from the pump. (Note: In acute massive overdose, hyperkalemia may occur; in such cases, K+ is contraindicated). * **B. Lidocaine:** This is the drug of choice for treating digoxin-induced ventricular arrhythmias because it suppresses abnormal ventricular automaticity without significantly depressing AV conduction. * **C. Phenytoin:** It is particularly useful for digoxin-induced atrial tachycardias with AV block, as it can suppress ectopic foci while actually improving AV conduction. **High-Yield Clinical Pearls for NEET-PG:** * **Antidote of Choice:** Digoxin-specific antibody fragments (**DigiFab/Digibind**) is the definitive treatment for life-threatening toxicity. * **Most Common Arrhythmia:** PVCs (Bigeminy). * **Most Characteristic Arrhythmia:** Atrial Tachycardia with high-grade AV block. * **Visual Side Effect:** Xanthopsia (yellow-green halos around lights). * **ECG Changes (Therapeutic):** "Reverse Tick" or "Sagging" ST-segment depression.

Q: A young man with known heroin addiction is brought to the emergency department in an unconscious state. On examination, the patient has decreased bowel sounds, depressed respiration, and pinpoint pupils. What is the treatment of choice for this patient?

IV naloxone. ### Explanation **Correct Answer: B. IV naloxone** **Medical Concept:** The patient presents with the classic **"Opioid Overdose Triad"**: coma (unconscious state), respiratory depression, and miosis (pinpoint pupils). The presence of decreased bowel sounds further confirms opioid toxicity, as opioids slow gastrointestinal motility. In an acute emergency involving respiratory depression, the treatment of choice is **IV Naloxone**. Naloxone is a competitive opioid receptor antagonist with a high affinity for $\mu$-receptors, rapidly reversing the life-threatening effects of the overdose. **Why Incorrect Options are Wrong:** * **A. Oral Naltrexone:** While naltrexone is an opioid antagonist, it is used for **relapse prevention** in detoxified patients. It has a slow onset and is administered orally, making it useless and dangerous (due to aspiration risk) in an acute emergency. * **C. Oral Diazepam:** Diazepam is a benzodiazepine. Giving a sedative to a patient with respiratory depression would worsen the condition and potentially lead to death. * **D. Oral Buprenorphine:** This is a partial $\mu$-agonist used for **maintenance therapy** or substitution. Administering it during an acute overdose would not reverse respiratory depression and could complicate the clinical picture. **High-Yield Clinical Pearls for NEET-PG:** * **Naloxone Half-life:** It has a shorter half-life (30–90 mins) than most opioids (e.g., methadone). Patients must be monitored closely for **"re-narcotization"** as the antagonist wears off. * **Pinpoint Pupils Exception:** Pethidine (Meperidine) overdose typically presents with **mydriasis** (dilated pupils) rather than miosis due to its atropine-like effects. * **Diagnostic Triad:** Coma + Pinpoint pupils + Respiratory rate < 12/min = Opioid Overdose until proven otherwise.

Q: Which of the following drugs does NOT produce gynecomastia?

Cortisol. Gynecomastia is the benign proliferation of glandular breast tissue in males, typically caused by an imbalance between estrogen and androgen effects [1]. **Why Cortisol is the Correct Answer:** **Cortisol** (Option C) is a glucocorticoid. While chronic excess of glucocorticoids (Cushing’s syndrome) can lead to fat redistribution (pseudogynecomastia), they do **not** cause true glandular proliferation. In fact, glucocorticoids are more likely to cause testicular atrophy and decreased libido rather than gynecomastia. **Why the other options are incorrect:** * **Cimetidine (Option A):** An H2-receptor antagonist that causes gynecomastia via two mechanisms: it acts as a weak anti-androgen (blocks androgen receptors) [2] and inhibits the cytochrome P450-mediated metabolism of estradiol. * **Digoxin (Option B):** It has a steroid-like structure that can bind to estrogen receptors. Chronic use increases estrogen levels and decreases luteinizing hormone (LH), leading to breast enlargement. * **Spironolactone (Option C):** A potassium-sparing diuretic and the most common drug-induced cause of gynecomastia. It acts as an androgen receptor antagonist and inhibits testosterone synthesis [1]. (Note: Eplerenone is a more selective alternative that does not cause this side effect). **NEET-PG High-Yield Pearls:** To remember the common drugs causing gynecomastia, use the mnemonic **"DISCO"**: * **D** – Digoxin * **I** – Isoniazid * **S** – Spironolactone * **C** – Cimetidine / Cyclophosphamide * **O** – Oestrogens / Oral contraceptives **Other notable causes:** Ketoconazole (inhibits steroid synthesis), Finasteride (5-alpha reductase inhibitor), and Marijuana.

Q: All of the following are parts of the treatment of Lithium toxicity, except:

Using an antagonist. **Explanation:** The correct answer is **D (Using an antagonist)** because there is **no specific pharmacological antagonist** available for Lithium. Lithium is a monovalent cation, and its toxicity is managed through supportive care and physical removal from the body rather than receptor blockade. **Analysis of Options:** * **Treating dehydration (A):** This is a cornerstone of management. Lithium is handled by the kidneys similarly to Sodium. Dehydration leads to compensatory proximal tubular reabsorption of Sodium and Lithium, worsening toxicity. Normal saline infusion helps restore volume and promotes Lithium excretion. * **Ingestion of polystyrene (B):** Specifically, **Sodium Polystyrene Sulfonate (Kayexalate)** or newer agents like **Patiromer** can be used. While primarily used for hyperkalemia, these cation-exchange resins can bind Lithium in the gastrointestinal tract, reducing its absorption. * **Hemodialysis (C):** This is the **treatment of choice** for severe Lithium toxicity (levels >4 mEq/L or >2.5 mEq/L with symptoms). Lithium is an ideal candidate for dialysis because it is a small molecule, has a low volume of distribution, and is not protein-bound. **NEET-PG High-Yield Pearls:** 1. **Therapeutic Index:** Lithium has a very narrow therapeutic index (0.6–1.2 mEq/L). 2. **Drug Interactions:** Thiazides, NSAIDs, and ACE inhibitors increase Lithium levels by decreasing its renal clearance. 3. **Gastric Lavage:** Useful only if the patient presents very early (within 1 hour), but **Activated Charcoal is ineffective** as it does not bind to metals/ions like Lithium. 4. **Whole Bowel Irrigation:** Recommended for toxicity involving sustained-release preparations.

Q: A 29-year-old medical student developed a positive PPD test and was started on isoniazid (INH) and rifampin prophylaxis. Three months into her therapy, she began to experience muscle fasciculations and convulsions. Administration of which of the following vitamins might have prevented these symptoms?

Pyridoxine. **Explanation:** The clinical presentation of muscle fasciculations and convulsions in a patient taking **Isoniazid (INH)** is a classic manifestation of **Vitamin B6 (Pyridoxine) deficiency**. **Why Pyridoxine is the correct answer:** Isoniazid is structurally similar to pyridoxine. It causes deficiency through two primary mechanisms: 1. It inhibits the enzyme **pyridoxine phosphokinase**, which converts pyridoxine to its active form, pyridoxal-5-phosphate (PLP). 2. It reacts with PLP to form a hydrazone complex that is rapidly excreted in the urine. PLP is a vital cofactor for the enzyme **glutamic acid decarboxylase**, which converts glutamate (an excitatory neurotransmitter) into **GABA** (the primary inhibitory neurotransmitter). A lack of GABA leads to CNS over-excitation, resulting in muscle twitching, peripheral neuropathy, and seizures. **Why the other options are incorrect:** * **Niacin (B3):** While INH can theoretically cause Pellagra-like symptoms (as B6 is needed to convert tryptophan to Niacin), the acute neurological symptoms like convulsions are specifically due to GABA depletion from B6 deficiency. * **Riboflavin (B2) & Thiamine (B1):** Deficiency of these vitamins does not typically present with acute convulsions in the context of INH therapy. Thiamine deficiency is associated with Beriberi or Wernicke-Korsakoff syndrome. **NEET-PG High-Yield Pearls:** * **Prophylaxis:** To prevent neurotoxicity, 10–50 mg/day of Pyridoxine is co-administered with INH, especially in high-risk groups (alcoholics, diabetics, pregnant women, and "slow acetylators"). * **Treatment:** For INH-induced seizures, high doses of IV Pyridoxine are required to restore GABA levels. * **Metabolism:** INH is metabolized by **Acetylation** (Phase II reaction). Slow acetylators are at a higher risk of peripheral neuropathy.

Q: All of the following drugs are nephrotoxic, EXCEPT:

Chlorpromazine. The correct answer is **Chlorpromazine**. Chlorpromazine is a typical antipsychotic (phenothiazine) primarily metabolized by the liver. It is not associated with direct nephrotoxicity; instead, its significant side effects include extrapyramidal symptoms, cholestatic jaundice, and photosensitivity. **Analysis of Options:** * **Lithium (Option A):** Lithium is a classic nephrotoxic drug. It is excreted unchanged by the kidneys and can cause **Nephrogenic Diabetes Insipidus (NDI)** by interfering with ADH action in the collecting ducts. Long-term use can also lead to chronic interstitial nephritis. * **Gentamicin (Option B):** Aminoglycosides like Gentamicin are notorious for causing **Acute Tubular Necrosis (ATN)** [2]. They accumulate in the proximal convoluted tubule (PCT) cells, leading to dose-dependent, reversible renal failure [2]. * **Cephalosporins (Option D):** Certain cephalosporins (especially first-generation like Cephaloridine) are nephrotoxic. When used in high doses or combined with loop diuretics/aminoglycosides, they can cause tubular necrosis or interstitial nephritis. **NEET-PG High-Yield Pearls:** 1. **Drug-Induced NDI:** Lithium is the most common cause. Treatment involves stopping the drug and starting **Amiloride** (which blocks lithium entry into the ENaC channels). 2. **Aminoglycoside Toxicity:** Gentamicin causes ATN (nephrotoxicity) and ototoxicity [1], [2]. Nephrotoxicity is usually reversible, but ototoxicity is often permanent [2]. 3. **Amphotericin B:** Another high-yield nephrotoxic drug that causes "Type 1 Renal Tubular Acidosis" and significant potassium/magnesium wasting. 4. **Contrast-Induced Nephropathy:** Prevented primarily by adequate **pre-procedure hydration** with normal saline.

Q: All of the following predispose to chloroquine toxicity except?

Duration of use greater than 2 years. **Explanation:** Chloroquine and Hydroxychloroquine are associated with serious **retinal toxicity**. The risk of toxicity is primarily determined by the **cumulative dose** and the **duration of exposure**. According to the American Academy of Ophthalmology (AAO) guidelines, the critical threshold for duration of use is **greater than 5 years**, not 2 years. Therefore, Option A is the correct answer as it is not a standard predisposing factor. **Analysis of Options:** * **Option A (Correct):** Toxicity is rarely seen within the first 5 years of treatment. A duration of >5 years is considered a major risk factor. * **Option B (Incorrect):** A cumulative dose exceeding **460 g** for Chloroquine (or >1000 g for Hydroxychloroquine) significantly increases the risk of irreversible retinopathy. * **Option C (Incorrect):** High daily doses are the most significant predictors of toxicity. For Chloroquine, a dose **>2.3 mg/kg/day** (often rounded to >3 mg/kg or >250 mg/day) is considered high risk. * **Option D (Incorrect):** Since these drugs are cleared renally, **renal failure** increases the elimination half-life, leading to higher systemic levels and increased risk of toxicity. **High-Yield Clinical Pearls for NEET-PG:** * **Bull’s Eye Maculopathy:** The classic presentation of chloroquine retinopathy (bilateral, symmetrical granular pigmentary changes). * **Screening:** Baseline ophthalmic exam is required, followed by annual screening after 5 years of use. * **Mechanism:** Chloroquine binds to melanin in the Retinal Pigment Epithelium (RPE), leading to localized damage. * **Other Toxicities:** Myopathy, cardiomyopathy, and QT prolongation.

Question 1

Which of the following drugs can result in cyanide poisoning?

Accepted Answer

Sodium Nitroprusside

Answer

Amyl nitrite

Answer

Hydroxycobalamin

Answer

Sodium thiosulphate

Question 2

Hemodialysis is useful in treating poisoning with all of the following agents, EXCEPT:

Accepted Answer

Nifedipine

Answer

Salicylate

Answer

Barbiturates

Answer

Methanol

Question 3

Which of the following is NOT included in the treatment of digoxin overdose?

Accepted Answer

Hemodialysis

Answer

Potassium

Answer

Lidocaine

Answer

Phenytoin

Question 4

A young man with known heroin addiction is brought to the emergency department in an unconscious state. On examination, the patient has decreased bowel sounds, depressed respiration, and pinpoint pupils. What is the treatment of choice for this patient?

Accepted Answer

IV naloxone

Answer

Oral naltrexone

Answer

Oral diazepam

Answer

Oral buprenorphine

Question 5

Which of the following drugs does NOT produce gynecomastia?

Accepted Answer

Cortisol

Answer

Cimetidine

Answer

Digoxin

Answer

Spironolactone

Question 6

All of the following are parts of the treatment of Lithium toxicity, except:

Accepted Answer

Using an antagonist

Answer

Treating dehydration

Answer

Ingestion of polystyrene

Answer

Hemodialysis

Question 7

A 29-year-old medical student developed a positive PPD test and was started on isoniazid (INH) and rifampin prophylaxis. Three months into her therapy, she began to experience muscle fasciculations and convulsions. Administration of which of the following vitamins might have prevented these symptoms?

Accepted Answer

Pyridoxine

Answer

Niacin

Answer

Riboflavin

Answer

Thiamine

Question 8

A young man with a known history of heroin addiction is brought to the emergency department in an unconscious state by his friends. On examination, his pupils are pinpoint. What is the treatment of choice?

Accepted Answer

Intravenous naloxone

Answer

Oral naltrexone

Answer

Oral diazepam

Answer

Oral buprenorphine

Question 9

All of the following drugs are nephrotoxic, EXCEPT:

Accepted Answer

Chlorpromazine

Answer

Lithium

Answer

Gentamicin

Answer

Cephalosporins

Question 10

All of the following predispose to chloroquine toxicity except?

Accepted Answer

Duration of use greater than 2 years

Answer

Cumulative dose greater than 460 g

Answer

Daily dose greater than 250 mg/day or greater than 3 mg/kg

Answer

Renal failure

Clinical Pharmacology and Drug Toxicity — MCQs

Clinical Pharmacology and Drug Toxicity — MCQs

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