Clinical Pharmacology and Drug Toxicity — MCQs

A 34-year-old rickshaw puller who has been using heroin for the past 10 years was found unconscious by his family members and brought to the casualty. On examination, he exhibited bradycardia, shallow breathing, constricted pupils, a blood pressure of 100/70 mmHg, brisk bilateral deep tendon reflexes, and flexor plantar reflexes on both sides. Which is the best treatment for him?

Q939

Amphotericin B toxicity can be lowered by:

Q940

Which of the following treatments is not indicated in digitalis poisoning?

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

Question 931: What is the antidote for Ethylene Glycol?

A. Barbiturate
B. Acetylcysteine
C. Ferric chloride
D. Fomepizole (Correct Answer)

Explanation: ***Fomepizole*** - **Fomepizole** is the primary and preferred antidote for ethylene glycol poisoning, as it competitively inhibits **alcohol dehydrogenase**, the enzyme responsible for metabolizing ethylene glycol into its toxic metabolites. - By blocking this enzyme, fomepizole prevents the formation of harmful compounds like **glycolic acid** and **oxalic acid**, which cause metabolic acidosis and kidney damage. - **Ethanol** is an alternative antidote that works by the same mechanism (competitive inhibition of alcohol dehydrogenase) and can be used when fomepizole is unavailable, though fomepizole is preferred due to better safety profile and easier dosing. *Barbiturate* - **Barbiturates** are a class of psychoactive drugs that act as central nervous system depressants, primarily used for sedation, anesthesia, and seizure control. - They have no role in neutralizing or metabolizing ethylene glycol or its toxic byproducts. *Acetylcysteine* - Acetylcysteine is an antidote primarily used for **acetaminophen (paracetamol) overdose**, where it replenishes glutathione stores and detoxifies its toxic metabolite, **NAPQI**. - It does not have any direct antidotal effect against ethylene glycol or its metabolites. *Ferric chloride* - **Ferric chloride** is a chemical compound used in various industrial processes, water treatment, and as a laboratory reagent. - It is highly corrosive and toxic if ingested, but it is not used as an antidote for any type of poisoning, including ethylene glycol.

Question 932: What is the mode of action of azathioprine?

A. ↑ IL-2
B. Decreased lymphophagocytic activity
C. Wide-spread antitumor activity
D. T-cell blockade (Correct Answer)

Explanation: ***T-cell blockade*** - Azathioprine is a **prodrug** that is metabolized into **6-mercaptopurine (6-MP)**, which then interferes with **purine synthesis** [1, 2]. - This interference inhibits the proliferation of **lymphocytes**, particularly **T-cells**, thereby blocking their immune response. *↑ IL-2* - An increase in **IL-2 (interleukin-2)** production would lead to enhanced T-cell proliferation and activity, which is the opposite effect of azathioprine. - **IL-2** is crucial for T-cell growth, differentiation, and survival, so drugs that increase it would boost, not suppress, the immune system. *Decreased lymphophagocytic activity* - This statement is not the primary mode of action of azathioprine. The drug's main effect is on the **synthesis of DNA and RNA** in rapidly dividing cells, including lymphocytes. - While immune suppression can indirectly affect various immune cell functions, the direct mechanism is not primarily a decrease in phagocytosis by lymphocytes. *Wide-spread antitumor activity* - Although 6-mercaptopurine, the active metabolite of azathioprine, is used in combination chemotherapy for some **hematological malignancies**, azathioprine itself is primarily known as an **immunosuppressant** in conditions like **autoimmune diseases** and **transplant rejection**. - Its antitumor activity is not typically described as "wide-spread," and its predominant use in pharmacology is for immune modulation.

Question 933: Which of the following best describes a Type B adverse drug reaction?

A. Augmented effect of drug
B. Effect seen on chronic use of drug
C. Delayed effect of drug
D. Unpredictable bizarre reaction (Correct Answer)

Explanation: ***Unpredictable bizarre reaction*** - Type B reactions are **unpredictable**, **bizarre**, and not directly related to the drug's known pharmacological actions. - They often involve **immunological reactions** or genetic predispositions, such as allergies or idiosyncratic responses. *Augmented effect of drug* - This describes a **Type A** adverse drug reaction, which is predictable and results from an **exaggerated pharmacological effect** of the drug. - It is typically dose-dependent and can be managed by adjusting the dosage. *Effect seen on chronic use of drug* - This description can apply to several types of adverse reactions, but it commonly relates to **Type C (chronic) reactions**, where effects occur only after prolonged exposure. - These reactions might be due to **cumulative toxicity** or adaptive changes in the body. *Delayed effect of drug* - This aligns with **Type D (delayed) adverse drug reactions**, which manifest long after the drug exposure has ended or after a period of latency. - Examples include **carcinogenesis** or teratogenesis, occurring months or years later.

Question 934: Long-term steroid ingestion leads to all of the following except:

A. Avascular necrosis of head of femur
B. Growth retardation
C. Hypoglycemia (Correct Answer)
D. Cataract

Explanation: ***Hypoglycemia*** - Chronic steroid use primarily leads to **hyperglycemia** due to increased **gluconeogenesis** and **insulin resistance**, not hypoglycemia. - Steroids raise blood glucose levels, potentially inducing or worsening **diabetes mellitus**. *Avascular necrosis of head of femur* - Long-term steroid use is a well-established risk factor for **avascular necrosis**, particularly affecting the **femoral head**. - This occurs due to impaired blood supply to the bone, leading to its death. *Cataract* - **Posterior subcapsular cataracts** are a known ocular complication of prolonged systemic corticosteroid therapy. - The mechanism involves direct effects of steroids on lens metabolism and protein aggregation. *Growth retardation* - In children, chronic corticosteroid therapy can suppress growth, leading to **growth retardation**. - This is due to interference with **growth hormone secretion** and direct effects on bone formation.

Question 935: What is the recommended dosage for chloroquine chemoprophylaxis in malaria prevention?

A. 500 mg/week
B. 400 mg once weekly
C. 500 mg once weekly (Correct Answer)
D. 500 mg BD/week

Explanation: ***500 mg once weekly*** - The recommended dosage for chloroquine chemoprophylaxis in malaria prevention is **500 mg salt** (or equivalent to 300 mg base) administered **once weekly**. - This regimen ensures adequate blood concentrations to prevent malarial infection in endemic areas. *500 mg/week* - While the 500 mg dose is correct, simply stating "500 mg/week" without specifying "once weekly" could be misinterpreted. - Chloroquine is generally taken as a **single weekly dose**, not divided doses. *400 mg once weekly* - A dosage of **400 mg** is **sub-therapeutic** for weekly chloroquine chemoprophylaxis. - This dose would likely not provide sufficient protection against malaria. *500 mg BD/week* - Taking chloroquine **twice weekly (BD/week)** at 500 mg is excessive for chemoprophylaxis. - This regimen can lead to increased side effects and toxicity without providing additional prophylactic benefit.

Question 936: Which tocolytic drug is most characteristically associated with pulmonary edema as an adverse effect?

A. Ritodrine (Correct Answer)
B. Indomethacin
C. Atosiban
D. Magnesium Sulfate

Explanation: ***Ritodrine*** * **Ritodrine** is a **beta-2 adrenergic agonist** that relaxes the uterus, but its non-selective nature can lead to adverse effects like **pulmonary edema** due to fluid retention and myocardial depression. * Other side effects include maternal tachycardia, palpitations, tremors, and hyperglycemia due to its systemic adrenergic activation. *Indomethacin (NSAID)* * **Indomethacin** is a **prostaglandin synthetase inhibitor** that can cause premature closure of the **ductus arteriosus** in the fetus if used for prolonged periods or late in gestation. * Maternal side effects typically include gastrointestinal upset, nausea, and heartburn, with pulmonary edema being extremely rare. *Atosiban (oxytocin receptor antagonist)* * **Atosiban** blocks oxytocin's action, a physiological mechanism for inhibiting uterine contractions, and is considered to have a generally favorable safety profile. * Common side effects are nausea, headache, and dizziness, and it is not associated with pulmonary edema. *Magnesium Sulfate* * **Magnesium sulfate** is a central nervous system depressant and calcium antagonist that can cause **respiratory depression** and **hypotension** in the mother, and rarely maternal pulmonary edema, especially with renal impairment or rapid infusion. * While it can cause pulmonary edema, it is less common than with beta-agonists like ritodrine and usually associated with specific risk factors or overdose.

Question 937: A child presented with a history of ingestion of an unknown plant and developed mydriasis, tachycardia, dry mouth, warm skin, and delirium. Which of the following groups of drugs is likely to be responsible for the symptoms of this child?

A. Anticholinergic (Correct Answer)
B. Sympathomimetic
C. Opioid
D. Benzodiazepine

Explanation: ***Anticholinergic*** - The constellation of mydriasis, tachycardia, dry mouth, warm skin, and delirium is classic for **anticholinergic toxicity**, often described as "hot as a hare, blind as a bat, dry as a bone, red as a beet, and mad as a hatter." - This toxidrome is caused by the blockade of **muscarinic acetylcholine receptors**, leading to widespread inhibition of parasympathetic nervous system functions. - Common plant sources include **Datura** (jimsonweed) and **Atropa belladonna** (deadly nightshade). *Sympathomimetic* - While **mydriasis** and **tachycardia** can be present, sympathomimetic toxicity typically causes **diaphoresis (sweating)** and **hypertension**, not dry skin and mouth. - Patients often present with agitation, paranoia, and potentially seizures, but the key differentiating factor is the presence of profuse sweating. *Opioid* - Opioid overdose is characterized by the classic triad of **miosis (pinpoint pupils)**, **respiratory depression**, and **CNS depression (coma)**, none of which are present in this case. - Other common symptoms include bradycardia, hypotension, and hypothermia, which are contrary to the child's presentation. *Benzodiazepine* - Benzodiazepine overdose typically causes **CNS depression** including drowsiness, ataxia, and slurred speech, but usually spares vital signs unless combined with other depressants. - **Mydriasis**, **tachycardia**, and **dry mouth** are not characteristic symptoms of benzodiazepine toxicity; pupils are typically normal or slightly dilated due to hypoxia in severe cases.

Question 938: A 34-year-old rickshaw puller who has been using heroin for the past 10 years was found unconscious by his family members and brought to the casualty. On examination, he exhibited bradycardia, shallow breathing, constricted pupils, a blood pressure of 100/70 mmHg, brisk bilateral deep tendon reflexes, and flexor plantar reflexes on both sides. Which is the best treatment for him?

A. Buprenorphine
B. Flumazenil
C. Methadone
D. Naloxone (Correct Answer)

Explanation: ***Naloxone*** - The patient presents with classic signs of **opioid overdose**: unconsciousness, bradycardia, shallow breathing, and constricted pupils. **Naloxone** is a potent opioid antagonist that rapidly reverses these effects. - Its rapid onset of action and ability to displace opioids from receptors makes it the **gold standard** emergency treatment for opioid overdose. *Buprenorphine* - This is a **partial opioid agonist** used for **opioid dependence treatment**, not for acute overdose reversal. - While it can partially antagonize other opioids, its primary role is in addiction management, not rapid resuscitation. *Flumazenil* - **Flumazenil** is an antagonist used to reverse the effects of **benzodiazepines**, not opioids. - Administering flumazenil in an opioid overdose would be ineffective and potentially dangerous if co-ingestion of benzodiazepines is suspected but not predominant. *Methadone* - **Methadone** is a **long-acting opioid agonist** used for **opioid dependence treatment** and chronic pain management. - Administering methadone to an acutely overdosed patient would worsen their condition by adding more opioid effect.

Question 939: Amphotericin B toxicity can be lowered by:

A. Using Liposomal delivery systems (Correct Answer)
B. Reducing the dose
C. Combining with flucytosine
D. Administering with saline hydration

Explanation: ***Using Liposomal delivery systems*** - **Liposomal amphotericin B** significantly reduces toxicity by encapsulating the drug, thereby decreasing its direct contact with human cells, particularly kidney cells. - This delivery system allows for higher doses of amphotericin B to be administered with fewer side effects, especially **nephrotoxicity** and **infusion-related reactions**. - This is the **primary and most effective method** to lower amphotericin B toxicity while maintaining therapeutic efficacy. *Administering with saline hydration* - Hydration with **normal saline (0.9% NaCl)** is a general supportive measure during amphotericin B infusion to help mitigate **nephrotoxicity** by maintaining adequate renal perfusion. - While important for kidney protection and a standard adjunct to therapy, it does not directly alter drug-host cell interaction or intrinsic drug toxicity. - This is a supportive measure, not a primary method for lowering the systemic toxicity profile of the drug itself. *Reducing the dose* - While reducing the dose would lower toxicity, it would also likely compromise the **therapeutic efficacy** against severe fungal infections, which is often unacceptable given the life-threatening nature of these diseases. - This approach is generally reserved for situations where toxicity outweighs clinical benefit, necessitating a change in treatment strategy rather than a primary method for safe administration. *Combining with flucytosine* - Combining amphotericin B with **flucytosine** is a strategy to achieve a synergistic fungicidal effect and reduce the individual doses required, but flucytosine itself can have **bone marrow suppression** and other toxicities. - This combination enhances antifungal efficacy and can allow for *lower doses of amphotericin B*, indirectly reducing its toxicity, but it introduces the toxicity profile of flucytosine and is not a direct method to *lower amphotericin B's intrinsic toxicity*.

Question 940: Which of the following treatments is not indicated in digitalis poisoning?

A. Potassium
B. Hemodialysis (Correct Answer)
C. Phenytoin
D. Lidocaine

Explanation: ***Hemodialysis*** - **Digitoxin** and **digoxin** have large volumes of distribution and are extensively protein-bound, making them poorly dialyzable. - Therefore, **hemodialysis** is generally not effective in removing these cardiac glycosides from the body in cases of poisoning. *Potassium* - **Hypokalemia** can exacerbate digitalis toxicity by increasing digitalis binding to the Na+/K+ ATPase, thus potassium supplementation is indicated. - However, in cases of **hyperkalemia** due to severe poisoning, potassium administration would be contraindicated. *Phenytoin* - **Phenytoin** is an antiarrhythmic drug that can be used to treat **digitalis-induced tachyarrhythmias**, particularly ventricular arrhythmias. - It works by **suppressing ventricular ectopy** and improving AV nodal conduction. *Lidocaine* - **Lidocaine** is a Class IB antiarrhythmic that is effective in treating **ventricular arrhythmias** caused by digitalis toxicity. - It acts by **blocking sodium channels** and reducing automaticity in the ventricles, thereby stabilizing the cardiac membrane.

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