Clinical Pharmacology and Drug Toxicity Practice Questions

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: Isoniazid-induced peripheral neuropathy responds to administration of:

Pyridoxine. **Explanation:** **Mechanism of Action (Why Pyridoxine is Correct):** Isoniazid (INH) is a structural analog of **Pyridoxine (Vitamin B6)**. It induces peripheral neuropathy through two primary mechanisms: 1. **Competitive Inhibition:** INH inhibits the enzyme *pyridoxine phosphokinase*, which converts pyridoxine into its active form, **pyridoxal-5-phosphate (PLP)**. 2. **Increased Excretion:** INH reacts with pyridoxine to form isoniazid-pyridoxal hydrazones, which are rapidly excreted in the urine. PLP is a vital cofactor for the synthesis of neurotransmitters like GABA. A deficiency leads to axonal degeneration, manifesting as "stocking-and-glove" paresthesia. Administering exogenous Pyridoxine bypasses this deficiency. **Analysis of Incorrect Options:** * **Riboflavin (B2):** Deficiency typically causes cheilosis, glossitis, and corneal vascularization, not peripheral neuropathy. * **Thiamine (B1):** Deficiency causes Beriberi (Dry/Wet) and Wernicke-Korsakoff syndrome. While Dry Beriberi involves neuropathy, it is not the mechanism behind INH toxicity. * **Cobalamin (B12):** Deficiency leads to Subacute Combined Degeneration (SCD) of the spinal cord and megaloblastic anemia. **NEET-PG High-Yield Pearls:** * **Prophylactic Dose:** 10 mg/day of Pyridoxine is given to high-risk patients (diabetics, alcoholics, pregnant women, and malnourished individuals) starting INH. * **Therapeutic Dose:** If neuropathy develops, the dose is increased to 100 mg/day. * **Pharmacogenetics:** **Slow acetylators** are at a significantly higher risk of developing INH-induced peripheral neuropathy due to higher plasma concentrations of the drug. * **Other Side Effects:** INH is also associated with **Hepatotoxicity** (most common) and **Drug-induced Lupus** (anti-histone antibodies positive).

Q: What is the chemical name for Ecstasy?

MDMA. **Explanation:** **MDMA (3,4-Methylenedioxymethamphetamine)** is the correct chemical name for the recreational drug commonly known as **Ecstasy** or "Molly." It is a synthetic derivative of amphetamine that acts as a central nervous system stimulant and hallucinogen. **Mechanism of Action:** MDMA primarily works by reversing the action of the serotonin transporter (SERT), leading to a massive release of **serotonin** into the synaptic cleft. To a lesser extent, it also increases dopamine and norepinephrine levels. This results in heightened mood, empathy, and altered sensory perception. **Analysis of Options:** * **Option A (MDMA):** Correct. It stands for Methylenedioxymethamphetamine. * **Option B (MDHA):** Incorrect. While Methylenedioxyhydroxyamphetamine exists as a metabolite, it is not the name for Ecstasy. * **Option C (EDHA):** Incorrect. This is often associated with chelating agents (like Ethylenediamine-N,N'-bis) used in agriculture, not pharmacology. * **Option D (MDAM):** Incorrect. This is a distractor and not a recognized pharmacological abbreviation for this class of drugs. **Clinical Pearls for NEET-PG:** 1. **Serotonin Syndrome:** Overdose or co-administration with SSRIs/MAOIs can lead to life-threatening serotonin syndrome (hyperthermia, rigidity, and autonomic instability). 2. **Hyponatremia:** MDMA users often develop dilutional hyponatremia due to excessive water intake ("water intoxication") combined with drug-induced SIADH. 3. **Bruxism:** A classic clinical sign of MDMA use is jaw clenching or teeth grinding. 4. **Post-use "Crash":** Users often experience depression and fatigue following use due to acute depletion of neuronal serotonin stores.

Q: A patient has subclinical folate deficiency. All of the following drugs can precipitate megaloblastic anemia in this patient except?

Chloroquine. **Explanation:** The correct answer is **Chloroquine**. Megaloblastic anemia is primarily caused by a deficiency or impaired utilization of **Folic acid (Vitamin B9)** or **Vitamin B12**, both of which are essential for DNA synthesis. **Why Chloroquine is the correct answer:** Chloroquine is an antimalarial and anti-inflammatory drug that does not interfere with folate metabolism, absorption, or DNA synthesis. Therefore, it does not precipitate megaloblastic anemia, even in patients with subclinical deficiency. **Why the other options are incorrect:** * **Alcohol:** Chronic alcohol consumption is a common cause of folate deficiency. It interferes with the enterohepatic circulation of folate, inhibits its absorption in the jejunum, and has a direct toxic effect on the bone marrow. * **Phenytoin:** This anticonvulsant reduces folate levels by inhibiting the enzyme intestinal conjugase (preventing absorption) and by inducing hepatic enzymes that increase folate catabolism. Long-term use frequently leads to subclinical folate deficiency. * **Sulfasalazine:** Used in inflammatory bowel disease, it acts as a competitive inhibitor of the reduced folate carrier (RFC), significantly impairing the intestinal absorption of dietary folate. **NEET-PG High-Yield Pearls:** 1. **DHFR Inhibitors:** Drugs like **Methotrexate, Pyrimethamine, and Trimethoprim** are classic causes of megaloblastic anemia as they inhibit Dihydrofolate Reductase. 2. **DNA Synthesis Inhibitors:** **5-Fluorouracil, Hydroxyurea, and Zidovudine (AZT)** can cause megaloblastic changes without necessarily lowering folate levels. 3. **Oral Contraceptives:** Can occasionally interfere with folate absorption. 4. **Management:** When treating megaloblastic anemia caused by DHFR inhibitors, **Folinic acid (Leucovorin)** is preferred over Folic acid to bypass the inhibited enzyme.

Q: All of the following drugs can cause cholestatic jaundice except:

Ethambutol. **Explanation:** The correct answer is **Ethambutol**. This question tests your ability to differentiate between types of drug-induced liver injury (DILI), specifically identifying which drugs cause **cholestatic** versus **hepatocellular** damage. **1. Why Ethambutol is the correct answer:** Ethambutol is primarily known for its **ocular toxicity** (optic neuritis). Unlike other first-line anti-tubercular drugs like Isoniazid, Rifampicin, and Pyrazinamide, Ethambutol is generally **not hepatotoxic**. It does not typically cause cholestasis or significant elevations in liver enzymes, making it the "safe" anti-TB drug in patients with pre-existing liver disease. **2. Why the other options are incorrect:** * **Chlorpromazine:** This is the classic prototype for **drug-induced cholestasis**. It causes a hypersensitivity-type reaction leading to "bland cholestasis" or inflammatory cholestatic jaundice. * **Erythromycin estolate:** This specific salt of erythromycin is notorious for causing **cholestatic hepatitis**, likely due to a hypersensitivity reaction. It is the most common cause of drug-induced jaundice in adults taking macrolides. * **Estrogens:** Found in oral contraceptives, estrogens interfere with the bile salt transport system (canalicular secretion), leading to **dose-dependent cholestasis**. **Clinical Pearls for NEET-PG:** * **Hepatocellular Damage (High ALT/AST):** Isoniazid, Pyrazinamide, Paracetamol, Halothane. * **Cholestatic Jaundice (High ALP/Bilirubin):** Chlorpromazine, Erythromycin estolate, Anabolic steroids, Oral Contraceptives, Methyltestosterone. * **Ethambutol Mnemonic:** Remember **"E"** for **E**ye (Optic neuritis) and **E**xcretion (Renal). It spares the liver! * **Optic Neuritis:** Patients on Ethambutol must be monitored for red-green color blindness and visual acuity changes.

Question 1

Which of the following statements about pegfilgrastim is true?

Accepted Answer

It decreases the risk of neutropenia in patients on anti-cancer therapy.

Answer

It is a short-acting drug.

Answer

It can be given orally.

Answer

It is recombinant G-CSF.

Question 2

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 3

Atropine is not used in the poisoning of which of the following substances?

Accepted Answer

Baygon

Answer

Parathion

Answer

Endrin

Answer

Tik 20

Question 4

Which of the following adverse effects can persist long after the offending drug has been withdrawn?

Accepted Answer

Tardive dyskinesia

Answer

Paradoxical tachycardia

Answer

Malignant hyperthermia

Answer

Gynaecomastia

Question 5

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

Accepted Answer

Mannitol

Answer

Octreotide

Answer

Vincristine

Answer

Carbamazepine

Question 6

Isoniazid-induced peripheral neuropathy responds to administration of:

Accepted Answer

Pyridoxine

Answer

Riboflavin

Answer

Thiamine

Answer

Cobalamin

Question 7

What is the chemical name for Ecstasy?

Accepted Answer

MDMA

Answer

MDHA

Answer

EDHA

Answer

MDAM

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

A patient has subclinical folate deficiency. All of the following drugs can precipitate megaloblastic anemia in this patient except?

Accepted Answer

Chloroquine

Answer

Alcohol

Answer

Phenytoin

Answer

Sulfasalazine

Question 10

All of the following drugs can cause cholestatic jaundice except:

Accepted Answer

Ethambutol

Answer

Chlorpromazine

Answer

Erythromycin estolate

Answer

Estrogens

Clinical Pharmacology and Drug Toxicity — MCQs

Clinical Pharmacology and Drug Toxicity — MCQs

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