Clinical Pharmacology and Drug Toxicity Practice Questions

Q: All of the following drugs may cause hyperkalemia except?

Amphotericin B. **Explanation:** The correct answer is **Amphotericin B**. This drug is a classic cause of **hypokalemia** (low potassium), not hyperkalemia. **1. Why Amphotericin B is the correct answer:** Amphotericin B is a polyene antifungal that increases the permeability of the distal renal tubular membrane. This leads to **Type 1 (Distal) Renal Tubular Acidosis (RTA)**. The increased membrane permeability causes a significant leak of potassium and magnesium into the urine, resulting in profound hypokalemia and hypomagnesemia. **2. Why the other options are incorrect (Causes of Hyperkalemia):** * **Cyclosporine:** This immunosuppressant causes hyperkalemia by inhibiting the action of aldosterone on the principal cells of the collecting duct and inducing renal tubular resistance to mineralocorticoids. * **Heparin:** Heparin (both UFH and LMWH) inhibits the synthesis of aldosterone in the adrenal cortex by reducing the number and affinity of angiotensin II receptors in the zona glomerulosa. * **NSAIDs:** These drugs inhibit prostaglandin synthesis. Prostaglandins (PGE2 and PGI2) normally stimulate renin release. By suppressing the Renin-Angiotensin-Aldosterone System (RAAS), NSAIDs reduce potassium excretion. **High-Yield Clinical Pearls for NEET-PG:** * **"K-Sparing" mnemonic for Hyperkalemia:** **K**-sparing diuretics (Spironolactone), **S**uccinylcholine, **P**rimarine (Heparin), **A**CE inhibitors/ARBs, **R**enal failure, **I**nfection/Inflammation (NSAIDs), **N**ephrotoxicity (Cyclosporine), **G**lucose (Beta-blockers). * **Amphotericin B Toxicity:** Often referred to as "Ampho-terrible" due to its side effects: Nephrotoxicity, Hypokalemia, Hypomagnesemia, and Infusion-related reactions (Chills/Rigors). * **Heparin-induced hyperkalemia** can occur even with low doses and typically manifests within 3–5 days of starting therapy.

Q: Which of the following statements about bupivacaine is incorrect?

It is less cardiotoxic than lignocaine.. ### Explanation **1. Why Option A is the Correct (Incorrect Statement):** Bupivacaine is significantly **more cardiotoxic** than lignocaine. While lignocaine is used as an anti-arrhythmic, bupivacaine has a high affinity for voltage-gated sodium channels in the myocardium and dissociates slowly during diastole ("slow-in, slow-out" kinetics). This leads to severe ventricular arrhythmias and cardiovascular collapse that is notoriously difficult to resuscitate. **2. Analysis of Other Options:** * **Option B (Toxicity and Adrenaline):** While adrenaline is often added to local anesthetics to prolong action via vasoconstriction, it can worsen bupivacaine-induced cardiotoxicity by enhancing the risk of ventricular arrhythmias and tachycardia. * **Option C (Duration of Action):** Bupivacaine is a long-acting amide local anesthetic. It is highly lipid-soluble and protein-bound, providing anesthesia for 3–6 hours, which is much longer than lignocaine (1–2 hours). * **Option D (Intravenous Administration):** Bupivacaine is strictly contraindicated for intravenous use (e.g., IV Regional Anesthesia/Bier’s Block) due to the high risk of systemic toxicity and cardiac arrest. **3. High-Yield Clinical Pearls for NEET-PG:** * **Lipid Rescue:** Intravenous **Lipid Emulsion (20%)** is the specific antidote for bupivacaine-induced systemic toxicity (LAST). * **Levobupivacaine & Ropivacaine:** These are S-enantiomers developed to provide similar long-acting anesthesia but with a **lower risk** of cardiotoxicity compared to racemic bupivacaine. * **Potency:** Bupivacaine is roughly 4 times more potent than lignocaine. * **Differential Block:** At low concentrations, bupivacaine produces a sensory block with minimal motor block, making it ideal for **obstetric analgesia** (painless labor).

Q: Which of the following drugs causes nephrotoxicity and hypertension, similar to cyclosporine?

Tacrolimus. **Explanation:** The correct answer is **Tacrolimus (D)**. Both Cyclosporine and Tacrolimus belong to the class of **Calcineurin Inhibitors (CNIs)**. Their mechanism involves inhibiting calcineurin, which prevents the dephosphorylation of NFAT (Nuclear Factor of Activated T-cells), thereby decreasing IL-2 production and T-cell activation. Because they share the same mechanism of action, they also share a similar side-effect profile. The most characteristic toxicities of CNIs are **nephrotoxicity** (due to afferent arteriolar vasoconstriction) and **hypertension**. While Tacrolimus is more potent and associated with a higher incidence of post-transplant diabetes mellitus (neurotoxicity/hyperglycemia), it mirrors Cyclosporine’s renal and vascular adverse effects. **Analysis of Incorrect Options:** * **A. Azathioprine:** A purine antimetabolite. Its primary dose-limiting toxicity is **bone marrow suppression** (leukopenia) and potential hepatotoxicity. It does not cause hypertension or significant nephrotoxicity. * **B. Cyclophosphamide:** An alkylating agent. Its signature toxicity is **hemorrhagic cystitis** (prevented by Mesna) and bone marrow suppression. * **C. Mycophenolate mofetil (MMF):** Inhibits IMDH (Inosine Monophosphate Dehydrogenase). Its main side effects are **gastrointestinal** (diarrhea, vomiting) and hematological (pancytopenia). It is notably "renal-sparing." **NEET-PG High-Yield Pearls:** * **Gingival Hyperplasia & Hirsutism:** Common with Cyclosporine, but **absent** with Tacrolimus. * **Diabetes Mellitus:** More common with Tacrolimus than Cyclosporine. * **Drug of Choice:** Tacrolimus is currently preferred over Cyclosporine for most solid organ transplants due to superior efficacy and a slightly better cosmetic profile.

Q: What is the action of toxic doses of local anesthetics on the CNS?

First stimulating the CNS followed by depression. **Explanation:** The central nervous system (CNS) is highly sensitive to local anesthetic (LA) toxicity. The progression of symptoms follows a predictable biphasic pattern: **Initial Stimulation followed by Depression.** **1. Why Option A is Correct:** Local anesthetics work by blocking voltage-gated sodium channels. In the CNS, LAs initially block **inhibitory pathways** (specifically the inhibitory interneurons, such as GABAergic neurons). This "disinhibition" allows excitatory neurons to function unopposed, leading to signs of stimulation (agitation, tremors, and seizures). As the plasma concentration increases further, the LAs eventually block both inhibitory and **excitatory pathways**, resulting in generalized CNS depression (coma and respiratory arrest). **2. Why Other Options are Incorrect:** * **Option B:** This is physiologically incorrect; stimulation always precedes depression because inhibitory neurons are more sensitive to the block than excitatory ones. * **Option C & D:** These are incomplete. While depression (C) or stimulation (D) occurs, they represent different stages of the same toxicological spectrum. **Clinical Pearls for NEET-PG:** * **Early Signs of Toxicity:** Perioral numbness, metallic taste, tinnitus, and lightheadedness. * **The "Bupivacaine Exception":** While most LAs follow this CNS pattern, Bupivacaine is notoriously more **cardiotoxic** than neurotoxic. It can cause sudden refractory ventricular arrhythmias even before significant CNS symptoms appear. * **Management:** The definitive treatment for Local Anesthetic Systemic Toxicity (LAST) is **Intravenous Lipid Emulsion (20% Intralipid)**, which acts as a "lipid sink" to sequester the drug from tissues. * **Potentiation:** Hypercapnia (high $CO_2$) and acidosis lower the seizure threshold for local anesthetics.

Q: Which of the following drugs does NOT cause dilated cardiomyopathy?

Sacubitril. **Explanation:** The correct answer is **Sacubitril**. **Why Sacubitril is the correct answer:** Sacubitril is a **Neprilysin inhibitor**. It prevents the degradation of natriuretic peptides (ANP, BNP), leading to vasodilation, natriuresis, and inhibition of cardiac remodeling. Far from causing cardiomyopathy, Sacubitril (combined with Valsartan as ARNI) is a **cornerstone therapy used to treat** Heart Failure with Reduced Ejection Fraction (HFrEF) because it improves cardiac function and reduces mortality. **Why the other options are incorrect:** * **Doxorubicin & Daunorubicin (Anthracyclines):** These are classic causes of **Type I Chemotherapy-Induced Cardiotoxicity**. They generate reactive oxygen species (ROS) that cause irreversible myocyte damage and replacement fibrosis, leading to dose-dependent dilated cardiomyopathy. * **Trastuzumab:** This monoclonal antibody (anti-HER2) causes **Type II Cardiotoxicity**. Unlike anthracyclines, it leads to a reversible decrease in myocardial contractility (stunning) without structural damage, but it still manifests clinically as dilated cardiomyopathy/heart failure. **High-Yield Clinical Pearls for NEET-PG:** 1. **Anthracycline Toxicity:** Characterized by "biopsy-proven" myofibrillar loss. Risk is minimized by using **Dexrazoxane** (an iron chelator). 2. **Trastuzumab Toxicity:** Not dose-dependent and usually reversible upon discontinuation. 3. **ARNI (Sacubitril/Valsartan):** Requires a **36-hour washout period** when switching from an ACE inhibitor to prevent the risk of angioedema. 4. **Other drugs causing Dilated Cardiomyopathy:** Alcohol (most common toxin), Cocaine, Chloroquine, and Cyclophosphamide.

Q: Which of the following agents can help in the elimination of 15-20 tablets of 10 mg dextroamphetamine?

Ammonium chloride. **Explanation:** The correct answer is **Ammonium chloride**. This question tests the concept of **ion trapping** and the manipulation of urinary pH to enhance drug excretion. **1. Why Ammonium chloride is correct:** Dextroamphetamine is a **weakly basic drug**. According to the Henderson-Hasselbalch principle, basic drugs are more ionized (charged) in an acidic environment. Ionized molecules are lipid-insoluble and cannot be reabsorbed across the renal tubule back into the bloodstream. **Ammonium chloride** is a urinary acidifier; by lowering the urinary pH, it promotes the ionization of dextroamphetamine, "trapping" it in the urine and accelerating its elimination. **2. Why the other options are incorrect:** * **Acetazolamide:** This is a carbonic anhydrase inhibitor that causes **alkalinization** of the urine. This would decrease the excretion of basic drugs like amphetamines. * **Sodium bicarbonate:** This is a systemic and urinary **alkalinizer**. It is the treatment of choice for salicylate (aspirin) or barbiturate poisoning (weakly acidic drugs) but is contraindicated here as it would increase the reabsorption of amphetamines. * **Penicillamine:** This is a **chelating agent** used primarily in the treatment of Wilson’s disease (copper poisoning) and heavy metal toxicity (lead, mercury). It has no role in altering urinary pH for amphetamine clearance. **Clinical Pearls for NEET-PG:** * **Mnemonic:** "Acidify for Bases, Alkalinize for Acids." * **Acidic drugs** (e.g., Aspirin, Barbiturates, Methotrexate) → Excretion is enhanced by **Sodium bicarbonate**. * **Basic drugs** (e.g., Amphetamines, Phencyclidine, Quinine) → Excretion is enhanced by **Ammonium chloride** or Ascorbic acid. * **Caution:** In modern clinical practice, forced acid diuresis is rarely used for amphetamine overdose due to the risk of aggravating **rhabdomyolysis-induced renal failure**. Management focuses on supportive care and benzodiazepines.

Q: Dilutional hyponatremia is a side effect of which of the following drugs, except?

Mannitol. **Explanation:** The question asks to identify the drug that does **not** cause dilutional hyponatremia. **1. Why Mannitol is the Correct Answer:** Mannitol is an osmotic diuretic. When administered, it initially increases extracellular fluid volume by pulling water from the intracellular space. However, its primary therapeutic effect is to induce **osmotic diuresis**, leading to the loss of water in excess of electrolytes. This results in **hypernatremia** (due to dehydration) rather than dilutional hyponatremia [1]. While an initial "transitional" hyponatremia can occur due to ECF expansion, the hallmark clinical side effect of sustained mannitol use is hypernatremic dehydration [1]. **2. Why the other options are incorrect:** * **Vincristine & Carbamazepine:** Both are classic causes of **SIADH** (Syndrome of Inappropriate Antidiuretic Hormone secretion). Carbamazepine is known to potentiate the antidiuretic effects of peptides, contributing to hypotonic hyponatremia [2]. SIADH leads to excessive water reabsorption in the collecting ducts, resulting in hemodilution and **dilutional hyponatremia**. * **Octreotide:** While primarily used to treat variceal bleeding and acromegaly, Octreotide can induce hyponatremia by inhibiting glucagon and potentially interfering with free water clearance, though it is a less common cause than SIADH-inducing agents. **3. High-Yield Clinical Pearls for NEET-PG:** * **SIADH-Inducing Drugs (High Yield):** Remember the mnemonic "Cyclops Carb-Vinc": **Cyclo**phosphamide, **Carb**amazepine, **Vinc**ristine, and SSRIs [2]. * **Mannitol Contraindications:** It is contraindicated in active intracranial bleeding (except during craniotomy) and **congestive heart failure**, as the initial ECF expansion can worsen pulmonary edema. * **Drug of Choice for SIADH:** Tolvaptan or Conivaptan (V2 receptor antagonists).

Q: Fomepizole is used for the treatment of which type of poisoning?

Ethylene glycol poisoning. **Explanation:** **Fomepizole** is a potent competitive inhibitor of the enzyme **Alcohol Dehydrogenase (ADH)** [1]. In the management of toxic alcohol ingestions, specifically **Ethylene glycol** and **Methanol**, Fomepizole prevents the conversion of these parent compounds into their toxic metabolites [1,4]. 1. **Ethylene Glycol:** ADH converts it into glycoaldehyde, which eventually becomes **oxalic acid**, leading to metabolic acidosis and acute tubular necrosis (renal failure) [4,5]. By inhibiting ADH, Fomepizole halts the production of these toxins, allowing the parent compound to be excreted unchanged by the kidneys. 2. **Methanol:** Similarly, Fomepizole prevents the conversion of methanol into **formic acid**, which causes optic nerve damage and blindness [1,4]. **Analysis of Incorrect Options:** * **B. Ethyl alcohol poisoning:** Ethanol itself has a higher affinity for ADH than ethylene glycol. In fact, ethanol was historically used as an antidote for ethylene glycol before Fomepizole became the gold standard [1]. Fomepizole is not used to treat ethanol overdose. * **C. Ether poisoning:** Ether is an anesthetic agent; its toxicity is managed supportively (respiratory and cardiovascular stabilization) and does not involve the ADH pathway. * **D. Type A lactic acidosis:** This is caused by tissue hypoperfusion/hypoxia. Treatment focuses on correcting the underlying cause (e.g., shock, sepsis) rather than enzyme inhibition. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Fomepizole inhibits Alcohol Dehydrogenase (ADH) [1]. * **Indications:** Ethylene glycol and Methanol poisoning [2]. * **Advantage over Ethanol:** Fomepizole does not cause CNS depression or hypoglycemia and does not require constant blood level monitoring. * **Ethylene Glycol Hallmark:** Presence of **envelope-shaped calcium oxalate crystals** in urine and a high anion gap metabolic acidosis [4,5].

Q: In organophosphorus compound poisoning, atropine can reverse all the following signs except?

Muscle weakness. **Explanation:** Organophosphorus (OP) compounds inhibit the enzyme acetylcholinesterase, leading to an accumulation of acetylcholine (ACh) at both **muscarinic** and **nicotinic** receptors. **Why Muscle Weakness is the Correct Answer:** Muscle weakness and paralysis in OP poisoning are mediated by **nicotinic (N$_M$) receptors** at the neuromuscular junction [2]. Atropine is a competitive **muscarinic antagonist**; it has no effect on nicotinic receptors [2]. Therefore, while atropine can reverse life-threatening respiratory secretions, it cannot reverse skeletal muscle weakness or fasciculations. To treat nicotinic effects, oximes (like Pralidoxime) are required to reactivate the enzyme [1], [4]. **Why the other options are incorrect:** * **Lacrimation (A), Diaphoresis (B), and Diarrhea (C):** These are all classic **muscarinic (M$_3$) effects** of ACh excess [3]. Atropine effectively blocks muscarinic receptors in the lacrimal glands, sweat glands, and gastrointestinal smooth muscle, thereby reversing these symptoms [3]. Note: While sweat glands are innervated by sympathetic nerves, they utilize muscarinic receptors, making diaphoresis an atropine-reversible sign. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for OP Poisoning:** **DUMBELS** (Diarrhea, Urination, Miosis, Bradycardia/Bronchospasm, Emesis, Lacrimation, Salivation/Sweating). * **Atropine's Role:** It reverses all "DUMBELS" but does **not** treat muscle weakness or respiratory muscle paralysis [2]. * **Therapeutic Endpoint:** In OP poisoning, atropine is titrated until **"Atropinization"** occurs, characterized by the clearing of lung secretions (most important) and a heart rate >80 bpm. Mydriasis is a sign but not the primary endpoint. * **Oximes:** Must be given early (before "aging" of the enzyme occurs) to reverse nicotinic effects [1], [4].

Question 1

All of the following drugs may cause hyperkalemia except?

Accepted Answer

Amphotericin B

Answer

Cyclosporine

Answer

Heparin

Answer

NSAIDs

Question 2

Which of the following statements about bupivacaine is incorrect?

Accepted Answer

It is less cardiotoxic than lignocaine.

Answer

Its toxicity can be increased by adrenaline.

Answer

It has a long duration of action.

Answer

It cannot be given intravenously.

Question 3

Which of the following drugs causes nephrotoxicity and hypertension, similar to cyclosporine?

Accepted Answer

Tacrolimus

Answer

Azathioprine

Answer

Cyclophosphamide

Answer

Mycophenolate mofetil

Question 4

What is the action of toxic doses of local anesthetics on the CNS?

Accepted Answer

First stimulating the CNS followed by depression

Answer

First depressing the CNS followed by stimulation

Answer

Only depression of the CNS

Answer

Only stimulation of the CNS

Question 5

Which of the following drugs does NOT cause dilated cardiomyopathy?

Accepted Answer

Sacubitril

Answer

Daunorubicin

Answer

Trastuzumab

Answer

Doxorubicin

Question 6

Which of the following agents can help in the elimination of 15-20 tablets of 10 mg dextroamphetamine?

Accepted Answer

Ammonium chloride

Answer

Acetazolamide

Answer

Penicillamine

Answer

Sodium bicarbonate

Question 7

Dilutional hyponatremia is a side effect of which of the following drugs, except?

Accepted Answer

Mannitol

Answer

Octreotide

Answer

Vincristine

Answer

Carbamazepine

Question 8

Which of the following is not included in Phase I clinical trials of medicine?

Accepted Answer

Epilepsy patients

Answer

Healthy volunteers

Answer

Patients with end-stage disease

Answer

HIV drug trial

Question 9

Fomepizole is used for the treatment of which type of poisoning?

Accepted Answer

Ethylene glycol poisoning

Answer

Ethyl alcohol poisoning

Answer

Ether poisoning

Answer

Type A lactic acidosis

Question 10

In organophosphorus compound poisoning, atropine can reverse all the following signs except?

Accepted Answer

Muscle weakness

Answer

Lacrimation

Answer

Diaphoresis

Answer

Diarrhea

Clinical Pharmacology and Drug Toxicity — MCQs

Clinical Pharmacology and Drug Toxicity — MCQs

On this page

Practice by Chapter

Want unlimited practice?