Clinical Pharmacology and Drug Toxicity — MCQs

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

Question 941: Which adverse drug reaction is commonly associated with Haloperidol?

A. Acute Dystonia (Correct Answer)
B. Weight Gain
C. Sedation
D. Nausea

Explanation: ***Acute Dystonia*** - **Haloperidol** is a **first-generation antipsychotic** that potently blocks **dopamine D2 receptors**, especially in the **nigrostriatal pathway**. - This blockade can lead to acute, involuntary muscle contractions, known as **acute dystonia**, which often manifests as **torticollis**, **oculogyric crisis**, or **laryngospasm**. *Weight Gain* - While **weight gain** can occur with some antipsychotics, it is more commonly associated with **second-generation antipsychotics** (e.g., olanzapine, clozapine) due to their effects on histamine and serotonin receptors. - Haloperidol's risk of significant weight gain is generally considered to be lower. *Sedation* - **Sedation** can be an adverse effect of haloperidol, but it is not considered the **most common** or distinguishing adverse reaction compared to extrapyramidal symptoms. - Sedation is often a general side effect seen with many psychotropic medications. *Nausea* - **Nausea** is a possible gastrointestinal side effect of many medications, including haloperidol, but it is not a hallmark adverse reaction. - It is far less specific and less commonly problematic than the **extrapyramidal symptoms (EPS)** associated with haloperidol.

Question 942: Which drug causes renal papillary necrosis?

A. Acetophenetidin (Correct Answer)
B. Gentamicin
C. Gold
D. Methicillin

Explanation: ***Acetophenetidin*** - **Acetophenetidin** (also known as phenacetin) is a well-known cause of **analgesic nephropathy**, which commonly presents as **renal papillary necrosis**. - Its nephrotoxic effects are attributed to its metabolism, particularly in the renal medulla, leading to cellular damage and necrosis of the renal papillae. *Gentamicin* - Gentamicin is an **aminoglycoside antibiotic** that can cause **acute tubular necrosis** (ATN), a form of acute kidney injury. - While nephrotoxic, its primary mechanism of renal damage is distinct from the ischemic and direct toxic effects leading to papillary necrosis. *Gold* - Gold compounds (historically used for rheumatoid arthritis) can cause various renal toxicities, including **membranous glomerulonephropathy**. - Renal papillary necrosis is not a typical manifestation of gold toxicity. *Methicillin* - Methicillin (a penicillin-class antibiotic) is known to cause **acute interstitial nephritis (AIN)**, a hypersensitivity reaction affecting the renal tubules and interstitium. - This condition involves inflammation and edema but not primarily necrosis of the renal papillae.

Question 943: In all of the following conditions, prostanoids may be used, except:

A. Glaucoma
B. Gastric ulcer
C. Closure of PDA (Correct Answer)
D. Platelet coagulation disorders

Explanation: ***Closure of PDA*** - Prostanoids, specifically **prostaglandin E1 (PGE1)**, are used to **maintain patency** of the ductus arteriosus, not to close it. [1], [3] - **Inhibitors of prostaglandin synthesis**, such as indomethacin, are used to promote the closure of a patent ductus arteriosus (PDA). *Glaucoma* - **Prostaglandin F2̱ (PGF2̱) analogs** like latanoprost are a first-line treatment for **open-angle glaucoma**. [1], [2] - They work by **increasing uveoscleral outflow** of aqueous humor, thereby reducing intraocular pressure. [1] *Gastric ulcer* - The **synthetic prostaglandin E1 (PGE1) analog misoprostol** is used to prevent and treat **NSAID-induced gastric ulcers**. [1], [2] - It works by **inhibiting acid secretion**, enhancing mucosal blood flow, and increasing mucus and bicarbonate production. [1] *Platelet coagulation disorders* - **Prostacyclin (PGI2)**, a type of prostanoid, is a potent **vasodilator** and **inhibitor of platelet aggregation**. [1] - Analogs of prostacyclin, such as epoprostenol, are used in conditions like **pulmonary hypertension** and to **prevent clotting** in extracorporeal circulation (e.g., dialysis). [1]

Question 944: The characteristic finding in chloroquine retinopathy is

A. Retinopathy that resolves immediately after stopping the drug
B. Bull's eye maculopathy (Correct Answer)
C. Primarily CNS involvement rather than retinal
D. Vision loss that is usually reversible

Explanation: ***Correct: Bull's eye maculopathy*** - **Bull's eye maculopathy** is the **pathognomonic (characteristic) finding** of chloroquine retinopathy - This distinctive pattern shows a ring of pigmentary changes surrounding the fovea, resembling a bull's eye target - Results from **chloroquine accumulation in retinal pigment epithelium (RPE) cells**, leading to selective damage in the macular region - This finding is specifically tested on screening examinations like **fundus autofluorescence and spectral-domain OCT** *Incorrect: Primarily CNS involvement rather than retinal* - Chloroquine **primarily affects the retina**, not the CNS - this is why it's called chloroquine **retinopathy** - While chloroquine can cause CNS effects (psychosis, seizures) at toxic doses, the main concern with chronic use is **irreversible retinal damage** - Regular **ophthalmologic screening** is mandatory precisely because retinal toxicity is the primary limiting side effect *Incorrect: Vision loss that is usually reversible* - Vision loss from chloroquine retinopathy is **typically IRREVERSIBLE** once significant damage occurs - The drug continues to be released from tissue stores even after discontinuation due to its **extremely long half-life** (weeks to months) - Early detection through screening is critical to **prevent irreversible blindness** - This is why regular monitoring with fundoscopy, visual field testing, and OCT is essential for patients on long-term therapy *Incorrect: Retinopathy that resolves immediately after stopping the drug* - Chloroquine retinopathy can actually **progress even after drug cessation** - a phenomenon called "rebound toxicity" - Due to chloroquine's **long tissue half-life** and continued release from tissue stores (especially in RPE), retinal damage may continue or worsen for months after stopping - The drug accumulates in melanin-containing tissues and is released slowly over time - This underscores the importance of **early detection and prevention** rather than relying on drug discontinuation to halt progression

Question 945: Which of the following statements about phase IV clinical trials is correct?

A. It is primarily focused on the efficacy of the drug.
B. It involves monitoring the long-term effects and safety of drugs. (Correct Answer)
C. It is conducted before a drug is submitted for approval.
D. It focuses primarily on determining the optimal dosage for patients.

Explanation: ***It involves monitoring the long-term effects and safety of drugs.*** - **Phase IV clinical trials** are conducted **after a drug has been approved and marketed** to monitor its performance in the general population. - The primary goals include assessing the **long-term safety profile**, identifying rare adverse effects, and evaluating effectiveness under real-world conditions. *It is primarily focused on the efficacy of the drug.* - The primary focus on **drug efficacy** is typically addressed in **Phase II and Phase III clinical trials**, where controlled studies evaluate if the drug works as intended. - While efficacy is re-evaluated in real-world settings during Phase IV, it's not the primary or exclusive focus, which broadens to safety and comparative effectiveness. *It is conducted before a drug is submitted for approval.* - Trials conducted **before drug submission for approval** are typically **Phase I, Phase II, and Phase III clinical trials**, which are designed to establish safety, dosage, and initial efficacy. - **Phase IV trials** specifically begin **after a drug has received regulatory approval** and is available to the public. *It focuses primarily on determining the optimal dosage for patients.* - **Optimal dosage determination** is largely the domain of **Phase I and Phase II clinical trials**, where escalating doses are tested in small groups to identify a safe and effective range. - Phase IV studies might explore different dosing regimens in specific patient populations, but they do not primarily determine initial optimal dosing.

Question 946: What is the treatment for Dabigatran toxicity?

A. Protamine sulphate
B. Andexanet alfa
C. Idarucizumab (Correct Answer)
D. Argatroban

Explanation: ***Idarucizumab*** - **Idarucizumab** is a specific humanized monoclonal antibody fragment (Fab) that directly binds to dabigatran and its metabolites, effectively **reversing its anticoagulant effects**. - It is indicated for patients requiring urgent reversal of dabigatran's anticoagulant effects due to life-threatening or uncontrolled bleeding, or for emergency surgery/urgent procedures. *Protamine sulphate* - **Protamine sulphate** is used to reverse the anticoagulant effects of **heparin** and low molecular weight heparins, but it is ineffective against direct oral anticoagulants like dabigatran. - Its mechanism involves forming a stable ion pair with heparin, neutralizing its activity. *Andexanet alfa* - **Andexanet alfa** is a recombinant modified human factor Xa (FXa) decoy protein used to reverse the anticoagulant activity of **FXa inhibitors** (e.g., rivaroxaban, apixaban). - It does not bind to or reverse the effects of direct thrombin inhibitors like dabigatran. *Argatroban* - **Argatroban** is a **direct thrombin inhibitor** (similar mechanism of action to dabigatran) and is used as an anticoagulant, particularly in patients with heparin-induced thrombocytopenia. - It would worsen dabigatran toxicity rather than treat it, as both drugs inhibit thrombin.

Question 947: Which antidiabetic medication is safe in both liver and renal failure?

A. Linagliptin (Correct Answer)
B. None of the options
C. Insulin
D. Both

Explanation: ***Linagliptin*** - **Linagliptin** is unique among **DPP-4 inhibitors** and antidiabetic medications because it is primarily excreted unmetabolized via the **biliary/fecal route** (80-90%), with only minimal renal excretion - This unique pharmacokinetic profile makes it the **only antidiabetic medication that requires NO dose adjustment** in **renal impairment** of any severity, including end-stage renal disease - It is also **safe in hepatic impairment** as only a small fraction undergoes hepatic metabolism - **No dose adjustment needed** in either renal or hepatic failure makes it truly "safe" in both conditions *Insulin* - While insulin can be **used** in patients with renal and hepatic failure, it is **NOT considered safe without dose modification** - **In renal failure:** Insulin clearance decreases significantly, leading to **prolonged half-life** and increased risk of **hypoglycemia** → requires **dose reduction** (often 25-50% decrease) - **In hepatic failure:** Impaired gluconeogenesis and altered insulin metabolism increase hypoglycemia risk → requires **careful dose reduction and monitoring** - The need for significant dose adjustments and increased monitoring means insulin does NOT meet the criteria of being "safe" in both conditions without modification *Both* - This option is **incorrect** because while both medications can be used in renal and hepatic failure, only **linagliptin** is truly safe without dose adjustment - **Insulin requires substantial dose reduction** in both conditions due to decreased clearance and altered metabolism - In pharmacology, "safe" implies use without major modifications; insulin's requirement for careful dose titration disqualifies it from this definition *None of the options* - This is incorrect because **linagliptin** clearly meets the criteria of being safe in both liver and renal failure without dose adjustment - Linagliptin's predominantly non-renal excretion pathway is a well-established pharmacological advantage

Question 948: Which of the following is a serious adverse effect of prolonged sodium nitroprusside infusion due to cyanide toxicity?

A. Lactic acidosis (Correct Answer)
B. Hypotension
C. Headache
D. Lactic acidosis, psychosis, and headache

Explanation: ***Lactic acidosis*** - This is the correct answer as **lactic acidosis** is a serious adverse effect of sodium nitroprusside due to **cyanide toxicity**. - Sodium nitroprusside is metabolized to **cyanide**, which inhibits **cytochrome oxidase** in the mitochondrial electron transport chain, leading to **impaired aerobic metabolism** and accumulation of **lactate**. - This is particularly concerning with **prolonged infusions** (>24-48 hours) or in patients with **renal or hepatic dysfunction**. - Clinical monitoring includes **serum lactate levels** and **metabolic acidosis** on arterial blood gas. *Hypotension* - While **hypotension** is the primary pharmacological effect and most common adverse effect of sodium nitroprusside, it is **dose-dependent** and **reversible** with rate adjustment. - It is not specifically related to **cyanide toxicity** from prolonged use, which is what makes nitroprusside particularly dangerous. - Managed by **titrating infusion rate** and continuous **blood pressure monitoring**. *Headache* - **Headache** is a common side effect due to **cerebral vasodilation**, but it is generally **mild** and not considered a serious adverse effect. - Not related to the **cyanide toxicity** mechanism that makes prolonged sodium nitroprusside use hazardous. *Lactic acidosis, psychosis, and headache* - While this combination represents multiple effects that can occur with sodium nitroprusside, it is unnecessarily comprehensive for a single-best-answer question. - **Psychosis** can occur with severe cyanide toxicity but is less commonly emphasized than **lactic acidosis** as the key marker of toxicity. - The most clinically relevant single answer focusing on **cyanide toxicity** is **lactic acidosis**.

Question 949: What is the maximum dose of plain lignocaine (in mg) for adults?

A. 300 (Correct Answer)
B. 500
C. 700
D. 1000

Explanation: ***300 mg*** - The maximum recommended dose of **plain lidocaine** (without epinephrine) for adults is typically **300 mg** or 4.5 mg/kg, whichever is less. - Exceeding this dose can increase the risk of **systemic toxicity**, including central nervous system and cardiovascular effects. *500 mg* - This dose is generally considered the maximum for **lidocaine with epinephrine** in adults, as **epinephrine** causes vasoconstriction and delays systemic absorption of lidocaine. - For **plain lidocaine**, 500 mg would be an overdose and significantly increase the risk of toxicity. *700 mg* - This is well above the recommended maximum dose for both plain lidocaine and lidocaine with epinephrine, posing a **severe risk of toxicity**. - Such a high dose could lead to **seizures**, cardiac arrhythmias, and even **cardiac arrest**. *1000 mg* - This dose is extremely dangerous and far exceeds any recommended maximum for lidocaine, regardless of whether it contains epinephrine. - Administration of 1000 mg of lidocaine would almost certainly result in **severe and potentially fatal toxicity**.

Question 950: Which of the following is used as an antidote for organophosphorus poisoning?

A. N-acetyl cysteine
B. Physostigmine
C. Flumazenil
D. Pralidoxime aldoxime methiodide (PAM) (Correct Answer)

Explanation: ***Pralidoxime aldoxime methiodide (PAM)*** - **Pralidoxime (PAM)** is an **oxime reactivator** that works by regenerating the inhibited **acetylcholinesterase** enzyme, thereby reversing the effects of organophosphorus poisoning. - It is particularly effective in treating the **nicotinic symptoms** (e.g., muscle weakness, paralysis) of severe organophosphate poisoning. *N-acetyl cysteine* - **N-acetyl cysteine (NAC)** is the antidote for **acetaminophen (paracetamol) overdose**, not organophosphorus poisoning. - It works by replenishing **glutathione** stores, which are crucial for detoxifying acetaminophen metabolites. *Physostigmine* - **Physostigmine** is an **acetylcholinesterase inhibitor** that increases acetylcholine levels. - It is used to reverse the effects of **anticholinergic poisoning**, not organophosphorus poisoning, which overstimulates the cholinergic system. *Flumazenil* - **Flumazenil** is a **benzodiazepine receptor antagonist** used to reverse the sedative effects of **benzodiazepine overdose**. - It does not have any role in the treatment of organophosphorus poisoning.

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Principles of Clinical Pharmacology

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Therapeutic Drug Monitoring

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Drug Toxicity and Overdose

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Antidotes and Their Applications

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Management of Drug Poisoning

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Drug-Induced Liver Injury

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Drug-Induced Kidney Injury

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Drug-Induced Blood Dyscrasias

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Drug-Induced QT Prolongation

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Pharmacovigilance

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