Clinical Pharmacology and Drug Toxicity Practice Questions

Q: A 41-year-old woman with glaucoma is treated with acetazolamide. Several weeks later, she has an arterial pH of 7.34, an arterial PCO2 of 29 mm Hg, and a plasma HCO3- of 15 mEq/L. Which of the following abnormalities has this woman most likely developed?

Metabolic acidosis. ### **Explanation** **1. Why Metabolic Acidosis is Correct:** Acetazolamide is a **carbonic anhydrase inhibitor** that acts on the proximal convoluted tubule of the kidney. It inhibits the reabsorption of sodium bicarbonate ($NaHCO_3$), leading to "bicarbonate wasting" in the urine. * **Mechanism:** By preventing the conversion of $H_2CO_3$ to $H_2O$ and $CO_2$ in the lumen, it causes a significant loss of $HCO_3^-$ in the urine. * **Laboratory Findings:** The patient’s $HCO_3^-$ is low (15 mEq/L; Normal: 22–28), and the pH is acidic (7.34; Normal: 7.35–7.45). This confirms a **primary metabolic acidosis**. * **Compensation:** The low $PCO_2$ (29 mm Hg; Normal: 35–45) indicates that the lungs are compensating by "blowing off" $CO_2$ (respiratory compensation), but the primary insult remains metabolic. **2. Why Other Options are Wrong:** * **Metabolic Alkalosis:** This would present with an elevated pH (>7.45) and elevated $HCO_3^-$. Acetazolamide causes the opposite by depleting bicarbonate. * **Mixed Acidosis:** This would require both a low $HCO_3^-$ (metabolic) and a high $PCO_2$ (respiratory). Here, the $PCO_2$ is low, indicating appropriate compensation, not a primary respiratory disorder. * **Mixed Alkalosis:** This would involve an elevated pH with both high $HCO_3^-$ and low $PCO_2$. **3. NEET-PG High-Yield Pearls:** * **Type of Acidosis:** Acetazolamide causes a **Normal Anion Gap Metabolic Acidosis (NAGMA)**, specifically a Type 2 Renal Tubular Acidosis (RTA). * **Clinical Uses:** Glaucoma (decreases aqueous humor production), Altitude Sickness (induces metabolic acidosis to drive ventilation), and Idiopathic Intracranial Hypertension. * **Side Effects:** Hypokalemia, paresthesias, and sulfa-drug allergy cross-reactivity. * **Mnemonic for NAGMA:** **HARDUPS** (Hyperalimentation, Acetazolamide, Renal tubular acidosis, Diarrhea, Ureteroenteric fistula, Pancreatic fistula, Spironolactone).

Q: Which of the following drugs exhibits a narrow therapeutic window?

Imipramine. **Explanation** **Correct Answer: D. Imipramine** The **therapeutic window** (or index) is the range of drug dosages which can treat disease effectively without having toxic effects. Drugs with a **narrow therapeutic window** require precise dosing and often therapeutic drug monitoring (TDM) because the dose required for efficacy is very close to the dose that causes toxicity. **Imipramine**, a Tricyclic Antidepressant (TCA), is notorious for its narrow therapeutic index. In overdose, it leads to the "3 Cs": **C**oma, **C**onvulsions, and **C**ardiotoxicity (arrhythmias due to sodium channel blockade). Because of this narrow safety margin, TCAs have largely been replaced by SSRIs in clinical practice. **Analysis of Incorrect Options:** * **A. Captopril:** An ACE inhibitor used for hypertension. It has a wide therapeutic window; while it can cause hypotension or hyperkalemia, these are usually predictable and manageable over a broad dose range. * **B. Furosemide:** A loop diuretic. Although potent, it has a wide safety margin. Toxicity (ototoxicity or severe dehydration) typically occurs only at extremely high intravenous doses. * **C. Diazepam:** A Benzodiazepine. These drugs are characterized by a high therapeutic index, making them much safer in overdose compared to older sedatives like Barbiturates. **NEET-PG High-Yield Pearls:** * **Mnemonic for Narrow Therapeutic Index Drugs:** "**W**ith **L**ow **T**herapeutic **I**ndex, **D**ogs **G**et **P**oisoned" (**W**arfarin, **L**ithium, **T**heophylline, **I**mipramine/TCAs, **D**igoxin, **G**entamicin/Aminoglycosides, **P**henytoin). * **TDM Requirement:** Most narrow therapeutic index drugs require TDM to ensure plasma concentrations remain within the safe "window." * **Antidote for TCA Toxicity:** Sodium Bicarbonate (used specifically to treat QRS widening and arrhythmias).

Q: Alkalinity of urine is done in which of the following conditions?

Barbiturate poisoning. **Explanation:** The correct answer is **Barbiturate poisoning**. This is based on the principle of **ion trapping**, where the ionization of a drug is manipulated to prevent its reabsorption in the renal tubules. 1. **Why Barbiturates?** Phenobarbital (a long-acting barbiturate) is a **weakly acidic drug**. According to the Henderson-Hasselbalch principle, acidic drugs become ionized (charged) in an alkaline medium. By administering Sodium Bicarbonate ($NaHCO_3$) to alkalinize the urine (pH 7.5–8.5), the barbiturate molecules become ionized. Since ionized drugs are lipid-insoluble, they cannot cross the tubular membrane back into the blood and are "trapped" in the urine, significantly increasing their renal clearance. 2. **Why the other options are incorrect:** * **Lithium:** Lithium is an alkali metal ion, not a weak acid or base. Its excretion depends on sodium levels and glomerular filtration; alkalinization does not affect its ionization or clearance. Hemodialysis is the treatment of choice for severe toxicity. * **Alprazolam & Diazepam:** These are Benzodiazepines (BZDs). While they are technically weak bases, they have a very high volume of distribution ($V_d$) and are highly protein-bound. Forced diuresis or pH manipulation is ineffective for drugs with high $V_d$. The specific antidote for BZD overdose is Flumazenil. **High-Yield Clinical Pearls for NEET-PG:** * **Urinary Alkalinization** is indicated for: **Salicylates (Aspirin)**, **Phenobarbital**, **Methotrexate**, and **Chlorpropamide**. * **Urinary Acidification** (using Ammonium Chloride) was historically used for weak bases like Amphetamines or Quinine, but it is **no longer recommended** clinically due to the risk of inducing severe systemic acidosis and rhabdomyolysis. * **Mnemonic:** "Acidic drugs need Alkaline urine" for excretion.

Q: Which drug commonly causes hypokalemia?

Amphotericin B. **Explanation:** **Amphotericin B (Correct Answer):** Amphotericin B is a potent antifungal that causes hypokalemia primarily through **renal tubular damage**. It increases the permeability of the distal tubular membrane by creating pores, leading to a "leak" of potassium ions into the urine. Additionally, it can cause Type 1 Renal Tubular Acidosis (RTA), further exacerbating potassium loss. **Analysis of Incorrect Options:** * **Insulin:** While insulin does cause a shift of potassium from the extracellular fluid into the cells (used acutely to treat hyperkalemia), it does not "commonly cause" clinical hypokalemia as a side effect in standard therapeutic settings, provided glucose is managed. * **Cyclosporine:** This immunosuppressant is notorious for causing **hyperkalemia** (not hypokalemia) by suppressing aldosterone activity and reducing potassium excretion in the collecting ducts. * **Carbenoxolone:** This drug (used for peptic ulcers) has mineralocorticoid-like activity, which can lead to sodium retention and potassium loss. However, it is rarely used in modern clinical practice compared to Amphotericin B, which is the classic high-yield association for drug-induced hypokalemia in exams. **High-Yield Clinical Pearls for NEET-PG:** 1. **Amphotericin B Toxicity:** Often presents as a triad of Nephrotoxicity, Hypokalemia, and Hypomagnesemia. 2. **Prevention:** Pre-loading with Normal Saline (saline loading) helps reduce the risk of Amphotericin-induced nephrotoxicity. 3. **Other Hypokalemia-inducing drugs:** Loop diuretics (Furosemide), Thiazides, Beta-2 agonists (Salbutamol), and Corticosteroids. 4. **Hyperkalemia-inducing drugs:** ACE inhibitors, ARBs, Spironolactone, and NSAIDs.

Q: Which of the following drugs does not exhibit nephrotoxicity?

Isoflurane. **Explanation:** The correct answer is **D. Isoflurane**. **1. Why Isoflurane is correct:** Isoflurane is a volatile anesthetic agent that undergoes minimal hepatic metabolism (only 0.2%). Unlike older agents like Methoxyflurane or Enflurane, it does not release significant amounts of inorganic fluoride ions, which are the primary cause of anesthetic-induced nephrotoxicity (fluoride-induced high-output renal failure). Isoflurane maintains stable renal blood flow and is considered safe for patients with renal impairment. **2. Why other options are incorrect:** * **Gentamicin & Streptomycin (Options A & B):** These are Aminoglycoside antibiotics. They are notoriously nephrotoxic because they are filtered by the glomerulus and actively reabsorbed by the proximal tubule cells, where they accumulate and cause acute tubular necrosis (ATN). Gentamicin is generally more nephrotoxic than Streptomycin. * **Methoxamine (Option C):** This is a potent alpha-1 adrenergic agonist. It causes intense systemic vasoconstriction, including the renal arteries. This significant reduction in renal blood flow can lead to ischemic renal injury and decreased glomerular filtration rate (GFR). **3. High-Yield Clinical Pearls for NEET-PG:** * **Methoxyflurane:** The most nephrotoxic volatile anesthetic (highest fluoride release). It is no longer used for general anesthesia. * **Sevoflurane:** Can react with soda lime in CO2 absorbers to produce **Compound A**, which is nephrotoxic in rats, though its clinical significance in humans remains debated. * **Desflurane & Isoflurane:** These are the safest volatile agents regarding renal function due to minimal metabolism. * **Aminoglycoside Nephrotoxicity:** Usually presents as non-oliguric renal failure and is typically reversible upon drug discontinuation.

Q: Skin pigmentation is known to occur with which of the following drugs?

Clofazimine, Minocycline, Rifampicin. **Explanation:** Drug-induced skin pigmentation is a high-yield topic in NEET-PG, involving various mechanisms such as melanin stimulation, drug deposition, or metabolite accumulation. **Why Option D is Correct:** * **Clofazimine:** A riminophenazine dye used in leprosy. It famously causes a **reddish-brown discoloration** of the skin and conjunctiva due to the accumulation of the drug in fatty tissues and the skin. * **Minocycline:** A tetracycline antibiotic known for causing **blue-grey pigmentation**. It can affect the skin (especially in scars), oral mucosa, and even bones or teeth. * **Rifampicin:** While primarily known for causing orange-red discoloration of body fluids (urine, sweat, tears), it can also lead to a transient **reddish-orange flushing** or pigmentation of the skin. **Analysis of Other Options:** * **Gold (Sodium aurothiomalate):** Causes a condition called **Chrysiasis**, characterized by a blue-grey permanent discoloration in sun-exposed areas. While Gold causes pigmentation, it is less commonly tested alongside Rifampicin/Clofazimine in this specific combination. * **Sulfonamides:** These are more frequently associated with **Fixed Drug Eruptions (FDE)**, which leave behind post-inflammatory hyperpigmentation, rather than generalized skin pigmentation as a direct side effect of the drug itself. **High-Yield Clinical Pearls for NEET-PG:** * **Amiodarone:** Causes a classic **slate-grey** (blue-man syndrome) pigmentation due to iodine content and lipofuscin deposition. * **Antimalarials (Chloroquine/Hydroxychloroquine):** Cause **blue-black** pigmentation, typically on the shins and oral mucosa. * **Cytotoxics:** **Busulfan** causes generalized "Addisonian-like" hyperpigmentation; **Bleomycin** causes characteristic **flagellate pigmentation**. * **Phenytoin:** Can cause chloasma-like facial pigmentation.

Q: N-acetylcysteine replenishes intracellular levels of which of the following?

Glutathione. **Explanation:** **Mechanism of Action:** N-acetylcysteine (NAC) is the specific antidote for **Paracetamol (Acetaminophen) poisoning**. Under normal conditions, a small portion of paracetamol is metabolized by the Cytochrome P450 system into a highly reactive and toxic metabolite called **NAPQI** (*N-acetyl-p-benzoquinone imine*). In therapeutic doses, NAPQI is immediately detoxified by conjugation with **Glutathione**. However, in an overdose, glutathione stores are depleted, leading to hepatic necrosis. NAC acts as a precursor for cysteine, which is the rate-limiting substrate for the synthesis of **Glutathione**, thereby replenishing its intracellular levels and facilitating the detoxification of NAPQI. **Analysis of Options:** * **Option A (Sodium) & Option B (Potassium):** These are primary extracellular and intracellular electrolytes, respectively. NAC does not play a role in the synthesis or regulation of these ions. Their levels are typically managed via intravenous fluids or specific ion-exchange resins. * **Option D:** Incorrect, as Glutathione is the well-established target of NAC therapy. **High-Yield Clinical Pearls for NEET-PG:** * **The "Golden Period":** NAC is most effective when administered within **8–10 hours** of paracetamol ingestion. * **Rumack-Matthew Nomogram:** This is used to determine the risk of hepatotoxicity based on plasma paracetamol levels vs. time since ingestion. * **Other Uses of NAC:** 1. **Mucolytic:** Breaks disulfide bonds in mucus (used in COPD/Cystic Fibrosis). 2. **Prevention of Contrast-Induced Nephropathy:** Though evidence is now debated, it is a classic exam fact. * **Route:** Can be given Orally (smells like rotten eggs due to sulfur) or Intravenously.

Q: Drug-induced psychosis occurs due to all the following drugs except?

Para-aminophenol. **Explanation:** The correct answer is **Para-aminophenol (Option D)**. **1. Why Para-aminophenol is correct:** Para-aminophenol is the parent chemical class of **Paracetamol (Acetaminophen)**. Paracetamol is a non-opioid analgesic and antipyretic that acts primarily by inhibiting prostaglandin synthesis in the CNS. It does not have any significant dopaminergic or serotonergic activity in the brain and is **not** associated with drug-induced psychosis. **2. Why the other options are incorrect:** * **Isoniazid (INH):** This anti-tubercular drug is a well-known cause of "INH psychosis." It interferes with Vitamin B6 (Pyridoxine) metabolism, which is a cofactor for the synthesis of GABA. A deficiency in GABA can lead to CNS excitation, seizures, and psychotic symptoms. * **Para-amino salicylic acid (PAS):** Another second-line anti-tubercular agent, PAS is known to cause various neuropsychiatric side effects, including acute psychosis and encephalopathy, though less frequently than INH. * **Lysergic acid derivatives (LSD):** LSD is a potent hallucinogen that acts as a partial agonist at **5-HT2A receptors**. It is a classic cause of drug-induced psychosis, characterized by vivid hallucinations and sensory distortions. **High-Yield Clinical Pearls for NEET-PG:** * **Dopamine Hypothesis:** Most drugs that cause psychosis (like Amphetamines, Cocaine, or Levodopa) increase dopamine levels in the mesolimbic pathway. * **Anticholinergic Psychosis:** Drugs like Atropine and Datura can cause "madness" (delirium/psychosis) due to central muscarinic blockade. * **Steroid Psychosis:** Glucocorticoids are a frequent cause of organic psychosis in clinical practice. * **Ketamine:** Acts as an NMDA receptor antagonist and can mimic the negative and positive symptoms of schizophrenia.

Q: What is the best treatment for severe digitalis toxicity?

Fab fragments of digitalis antibodies. ### Explanation **Correct Answer: D. Fab fragments of digitalis antibodies (Digibind)** **Why it is correct:** In cases of **severe digitalis toxicity** (characterized by life-threatening arrhythmias, hyperkalemia >5.5 mEq/L, or massive ingestion), **Digoxin-specific antibody fragments (Fab)** are the definitive treatment of choice. These fragments bind to free digoxin in the extracellular space, creating a complex that is rapidly excreted by the kidneys. This effectively lowers the free drug concentration and reverses the inhibition of the Na+/K+-ATPase pump. **Why the other options are incorrect:** * **A. Potassium supplements:** While hypokalemia predisposes to digitalis toxicity, severe toxicity itself often causes **hyperkalemia** (due to pump inhibition). Giving potassium in severe cases can be fatal. It is only used in mild toxicity with documented hypokalemia. * **B. Diphenylhydantoin (Phenytoin):** This was historically used to treat digitalis-induced ventricular arrhythmias because it suppresses abnormal automaticity without worsening AV block. However, it is not the "best" or definitive treatment for severe systemic toxicity. * **C. Quinidine:** This is **contraindicated**. Quinidine reduces the renal clearance of digoxin and displaces it from tissue binding sites, doubling the plasma concentration of digoxin and worsening toxicity. **High-Yield Clinical Pearls for NEET-PG:** * **Most common ECG finding:** Ventricular Bigeminy. * **Most characteristic ECG finding:** Bidirectional Ventricular Tachycardia. * **Earliest symptom:** Anorexia, nausea, and vomiting. * **Visual disturbance:** Xanthopsia (yellow-green vision). * **Electrolyte trigger:** Hypokalemia, hypomagnesemia, and hypercalcemia increase the risk of toxicity. * **Management of choice for Digoxin-induced Bradycardia:** Atropine.

Q: Neutropenia is caused by all of the following except?

Corticosteroids. ### Explanation **1. Why Corticosteroids are the Correct Answer:** Corticosteroids do **not** cause neutropenia; instead, they cause **Neutrophilic Leukocytosis** (an increase in the absolute neutrophil count). This occurs via three primary mechanisms: * **Demargination:** Neutrophils move from the endothelial walls (marginal pool) into the circulating pool. * **Delayed Apoptosis:** Steroids prolong the lifespan of circulating neutrophils. * **Stimulation of Bone Marrow:** They trigger the premature release of "bands" from the marrow. * *Note:* While they increase neutrophils, they cause a decrease in lymphocytes, eosinophils, and monocytes. **2. Analysis of Incorrect Options (Causes of Neutropenia):** * **Cephalosporins (B):** Beta-lactam antibiotics are a well-known cause of idiosyncratic drug-induced agranulocytosis or immune-mediated destruction of neutrophils. * **Ranitidine (C):** H2-receptor antagonists can cause bone marrow suppression, leading to reversible neutropenia or pancytopenia. * **Phenytoin (D):** This antiepileptic drug is associated with blood dyscrasias, including neutropenia and megaloblastic anemia (due to folate interference). **3. NEET-PG High-Yield Pearls:** * **Definition:** Neutropenia is defined as an Absolute Neutrophil Count (ANC) **<1500/µL**. Agranulocytosis is **<500/µL**. * **Most Common Drug Cause:** Globally, the most common drug associated with severe agranulocytosis is **Clozapine** (requires mandatory WBC monitoring). * **Other High-Yield Causes:** Antithyroid drugs (Methimazole/PTU), Chemotherapy, Sulfonamides, and Gold salts. * **Steroid Effect Mnemonic:** "Steroids make **B** neutrophils go **U**p and **L**ymphocytes go **U**p and **L**ymphocytes go **D**own" (BULD).

Question 1

A 41-year-old woman with glaucoma is treated with acetazolamide. Several weeks later, she has an arterial pH of 7.34, an arterial PCO2 of 29 mm Hg, and a plasma HCO3- of 15 mEq/L. Which of the following abnormalities has this woman most likely developed?

Accepted Answer

Metabolic acidosis

Answer

Metabolic alkalosis

Answer

Mixed acidosis

Answer

Mixed alkalosis

Question 2

Which of the following drugs exhibits a narrow therapeutic window?

Accepted Answer

Imipramine

Answer

Captopril

Answer

Furosemide

Answer

Diazepam

Question 3

Alkalinity of urine is done in which of the following conditions?

Accepted Answer

Barbiturate poisoning

Answer

Lithium toxicity

Answer

Alprazolam overdose

Answer

Diazepam toxicity

Question 4

Which drug commonly causes hypokalemia?

Accepted Answer

Amphotericin B

Answer

Insulin

Answer

Cyclosporine

Answer

Carbenoxolone

Question 5

Which of the following drugs does not exhibit nephrotoxicity?

Accepted Answer

Isoflurane

Answer

Gentamicin

Answer

Streptomycin

Answer

Methoxamine

Question 6

Skin pigmentation is known to occur with which of the following drugs?

Accepted Answer

Clofazimine, Minocycline, Rifampicin

Answer

Minocycline, Gold, Rifampicin

Answer

Clofazimine, Sulfonamides, Gold

Answer

Clofazimine, Gold, Rifampicin

Question 7

N-acetylcysteine replenishes intracellular levels of which of the following?

Accepted Answer

Glutathione

Answer

Sodium

Answer

Potassium

Answer

None of the above

Question 8

Drug-induced psychosis occurs due to all the following drugs except?

Accepted Answer

Para-aminophenol

Answer

Isoniazid

Answer

Para-amino salicylic acid

Answer

Lysergic acid derivatives

Question 9

What is the best treatment for severe digitalis toxicity?

Accepted Answer

Fab fragments of digitalis antibodies

Answer

Potassium supplements

Answer

Diphenylhydantoin

Answer

Quinidine

Question 10

Neutropenia is caused by all of the following except?

Accepted Answer

Corticosteroids

Answer

Cephalosporins

Answer

Ranitidine

Answer

Phenytoin

Clinical Pharmacology and Drug Toxicity — MCQs

Clinical Pharmacology and Drug Toxicity — MCQs

On this page

Practice by Chapter

Want unlimited practice?