Clinical Pharmacology and Drug Toxicity — MCQs

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

Question 691: Antidote for opioid poisoning:

A. Pethidine
B. Flumazenil
C. Naloxone (Correct Answer)
D. Physostigmine

Explanation: ***Naloxone*** - **Naloxone** is a pure **opioid antagonist** that reverses the effects of opioid overdose by competing for and binding to opioid receptors. - It is crucial in emergent situations to restore **respiratory drive** and consciousness in patients with opioid-induced respiratory depression. *Pethidine* - **Pethidine** is an **opioid analgesic** itself, primarily used for pain management, and would worsen opioid poisoning. - It works by binding to opioid receptors, leading to centrally mediated pain relief, making it contraindicated in overdose. *Flumazenil* - **Flumazenil** is an antagonist for **benzodiazepines**, used to reverse their sedative and respiratory depressant effects. - It has no effect on opioid receptors and would not be effective in treating opioid poisoning. *Physostigmine* - **Physostigmine** is a **cholinesterase inhibitor** used to reverse anticholinergic toxicity. - It increases acetylcholine levels at the synapse and is not indicated for opioid overdose.

Question 692: The drug of choice for hyperthyroidism in third trimester of pregnancy is:

A. Carbimazole (Correct Answer)
B. Sodium iodide
C. Radioactive iodine
D. Propylthiouracil

Explanation: ***Carbimazole*** - **Carbimazole** (metabolized to methimazole) is the **drug of choice in the third trimester** of pregnancy for managing hyperthyroidism. - The teratogenic risk of methimazole/carbimazole is confined to the **first trimester** (embryopathy includes aplasia cutis, choanal atresia, esophageal atresia). By the third trimester, organogenesis is complete and this risk has passed. - **Propylthiouracil (PTU)** is associated with severe **hepatotoxicity**, which is why current guidelines recommend switching from PTU to methimazole/carbimazole after the first trimester. - Both drugs cross the placenta, but in the third trimester, the safety profile favors carbimazole over PTU. *Propylthiouracil* - **PTU** is preferred only in the **first trimester** to avoid methimazole-associated congenital anomalies during the critical period of organogenesis. - After the first trimester, patients should be switched to methimazole/carbimazole due to PTU's risk of severe **hepatotoxicity** (including fulminant hepatic failure requiring transplantation). - PTU is not the drug of choice for the third trimester despite having lower placental transfer. *Sodium iodide* - **Sodium iodide** is used acutely in **thyroid storm** or as preoperative preparation for thyroidectomy, not for chronic management of hyperthyroidism. - Prolonged use can cause the **Wolff-Chaikoff effect** (temporary inhibition of thyroid hormone synthesis) followed by escape phenomenon and worsening hyperthyroidism. - Can cause fetal goiter and hypothyroidism with chronic use, making it unsuitable for long-term pregnancy management. *Radioactive iodine* - **Radioactive iodine** is **absolutely contraindicated** in pregnancy at any stage. - It crosses the placenta after 10-12 weeks of gestation and destroys the fetal thyroid gland, causing permanent **fetal hypothyroidism** and **cretinism**. - Must be avoided in pregnancy; pregnancy should be excluded before radioactive iodine therapy.

Question 693: Which of the following local anesthetics is the most common cause of methemoglobinemia?

A. Lignocaine
B. Benzocaine (Correct Answer)
C. Chloroprocaine
D. EMLA Cream (Lignocaine + Prilocaine)
E. Prilocaine
F. Dibucaine

Explanation: ***Benzocaine***- **Benzocaine** is an ester-type local anesthetic that is the **most common cause of methemoglobinemia** among local anesthetics, especially when used in high doses or on mucous membranes due to its rapid absorption.- Its metabolic byproducts, particularly **aniline derivatives**, are potent oxidizers of hemoglobin, converting the ferrous iron (Fe2+) to ferric iron (Fe3+), thus forming methemoglobin which cannot bind oxygen.- **FDA warnings** have been issued regarding benzocaine-induced methemoglobinemia, particularly with topical spray preparations.*Lignocaine*- **Lignocaine** (lidocaine) is an amide-type local anesthetic and is **rarely associated** with methemoglobinemia.- While it can theoretically cause it in very high doses, it is significantly **less potent** in this regard compared to benzocaine.*Chloroprocaine*- **Chloroprocaine** is an ester-type local anesthetic with a very **short duration of action** due to rapid hydrolysis by plasma cholinesterases.- This rapid metabolism typically limits systemic exposure and makes it an **uncommon cause** of methemoglobinemia despite being an ester.*Prilocaine*- **Prilocaine** is an amide-type local anesthetic that can also cause methemoglobinemia, particularly at **higher doses (>600mg)** [1, 2].- It works through its metabolite, **o-toluidine**, which is an oxidizing agent [1].- However, **benzocaine** is more consistently linked to this adverse effect in clinical practice and has more documented case reports.

Question 694: Which drug is used as a spermicidal cream in contraceptives?

A. Gossypol
B. Clomiphene
C. Nonoxynol-9 (Correct Answer)
D. Centchroman

Explanation: **Nonoxynol-9** - **Nonoxynol-9** is a common **spermicide** used in many contraceptive products like creams, foams, and gels. - It works by damaging the **sperm cell membrane**, effectively immobilizing and killing sperm. *Gossypol* - **Gossypol** is a natural compound found in cotton plants that has been studied for its potential as a **male contraceptive**. - It works by inhibiting **spermatogenesis** but has not been approved for widespread use due to toxicity concerns like **hypokalemia**. *Clomiphene* - **Clomiphene** is a **selective estrogen receptor modulator (SERM)** used to induce ovulation in women who are infertile due to anovulation. - It stimulates the release of **gonadotropins** (FSH and LH) from the pituitary gland, leading to follicular development. *Centchroman* - **Centchroman** (also known as Ormeloxifene) is a **non-steroidal oral contraceptive** used in India. - It acts as a **selective estrogen receptor modulator** in the uterus, disrupting the implantation process.

Question 695: Which of the following anti-diabetic drugs is associated with weight gain?

A. Pioglitazone (Correct Answer)
B. Acarbose
C. Metformin
D. Sitagliptin

Explanation: ***Pioglitazone*** - **Pioglitazone**, a **thiazolidinedione**, primarily works by improving insulin sensitivity in peripheral tissues. - Its mechanism of action can lead to **fluid retention** and **increased subcutaneous fat storage**, both contributing to weight gain. *Acarbose* - **Acarbose** is an **alpha-glucosidase inhibitor** that delays carbohydrate absorption in the gut. - This mechanism typically leads to a **neutral effect or slight weight loss**, as fewer calories are rapidly absorbed. *Metformin* - **Metformin**, a **biguanide**, reduces hepatic glucose production and improves insulin sensitivity. - It is often associated with **weight neutrality or modest weight loss**, and is not known to cause weight gain. *Sitagliptin* - **Sitagliptin** is a **dipeptidyl peptidase-4 (DPP-4) inhibitor** that enhances incretin effects. - This class of drugs is generally considered **weight-neutral** and rarely causes weight gain.

Question 696: Which of the following anti-epileptic drugs has the highest teratogenic potential?

A. Carbamazepine
B. Phenytoin
C. Valproate (Correct Answer)
D. Lamotrigine

Explanation: ***Correct: Valproate*** - **Valproate has the highest teratogenic potential** among all anti-epileptic drugs, with a **10-20% risk of major congenital malformations** - **Neural tube defects** (spina bifida) occur in **1-2% of exposed pregnancies**, which is 10-20 times higher than the general population - Other significant risks include **cardiac malformations, craniofacial abnormalities**, and **neurodevelopmental disorders** (autism spectrum disorder, reduced IQ) - **Fetal valproate syndrome** is a recognized clinical entity - Current guidelines strongly recommend **avoiding valproate in women of childbearing potential** unless no alternatives exist *Incorrect: Carbamazepine* - Has teratogenic risks but significantly **lower than valproate** (2-5% risk of major malformations) - Associated with **neural tube defects** (0.5-1% risk, lower than valproate) - Considered a safer alternative when valproate must be avoided *Incorrect: Phenytoin* - Causes **fetal hydantoin syndrome** with characteristic features: craniofacial anomalies, nail/digital hypoplasia, growth restriction, and developmental delay - Teratogenic risk is **moderate** (approximately 5-10% risk of major malformations) - Risk is significant but **lower than valproate** *Incorrect: Lamotrigine* - Considered **one of the safest anti-epileptic drugs** during pregnancy - Low teratogenic risk with **major malformation rate of 2-3%** (close to baseline population risk) - Slight increased risk of **oral clefts** at higher doses - **Preferred choice** for women of childbearing potential requiring anti-epileptic therapy

Question 697: Therapeutic drug monitoring is done for:

A. Aspirin
B. Heparin
C. Phenytoin (Correct Answer)
D. Metformin

Explanation: ***Phenytoin*** - **Phenytoin** has a **narrow therapeutic window**, meaning the difference between an effective and a toxic dose is small, necessitating close monitoring. - Its **variable absorption** and **nonlinear pharmacokinetics** (saturable metabolism) make individual dosing adjustments critical to maintain therapeutic levels and avoid toxicity. *Aspirin* - **Aspirin** is generally not monitored via plasma levels for its analgesic or antiplatelet effects, as its therapeutic effects are often observed at doses where plasma monitoring is not practical or necessary. - Its primary therapeutic use as an **antiplatelet agent** is evaluated by clinical outcomes rather than drug concentration. *Heparin* - **Heparin** is monitored using coagulation tests like **aPTT (activated partial thromboplastin time)** or anti-Xa levels to assess its anticoagulant effect, not direct drug concentration. - Therapeutic drug monitoring for heparin focuses on its **pharmacodynamic effects** on the clotting cascade rather than its absolute plasma concentration. *Metformin* - **Metformin** has a relatively **wide therapeutic index** and its efficacy is primarily measured by reductions in blood glucose and HbA1c, not by plasma drug concentrations. - It is excreted largely unchanged by the kidneys, and dose adjustments are typically made based on **renal function** and glycemic control.

Question 698: Antidote for benzodiazepine poisoning: FMGE 10, 13; NEET 14

A. Flumazenil (Correct Answer)
B. Naloxone
C. Atropine
D. N-acetyl-cysteine

Explanation: ***Flumazenil*** - **Flumazenil** is a competitive **benzodiazepine receptor antagonist** that can reverse the sedative and other central nervous system effects of benzodiazepines. - It works by blocking benzodiazepines from binding to their receptor sites on the **GABA-A receptor complex**. *Naloxone* - **Naloxone** is a competitive **opioid receptor antagonist** used to reverse opioid overdose. - It has no effect on **benzodiazepine toxicity** as it targets different receptor systems. *Atropine* - **Atropine** is an **anticholinergic drug** used to reverse the effects of **cholinergic poisoning** (e.g., from organophosphates, carbamates) or symptomatic bradycardia. - It works on muscarinic acetylcholine receptors and is not involved in benzodiazepine metabolism or action. *N-acetyl-cysteine* - **N-acetyl-cysteine (NAC)** is primarily used as an antidote for **acetaminophen (paracetamol) poisoning**, where it replenishes glutathione. - It is also used in some cases of mucolysis but has no role in reversing benzodiazepine toxicity.

Question 699: Which of the following is NOT used for iron poisoning?

A. EDTA (Ethylenediaminetetraacetic acid)
B. Desferrioxamine
C. Gastric lavage
D. Penicillamine (Correct Answer)

Explanation: ***Penicillamine*** - **Penicillamine** is a chelating agent indicated for **copper poisoning** (Wilson's disease), **lead poisoning**, and **rheumatoid arthritis**, but has **no role in iron poisoning**. - It works by chelating copper, lead, and other heavy metals, but does not effectively chelate iron. - This is the most clearly incorrect option as it is never indicated for iron toxicity. *EDTA (Ethylenediaminetetraacetic acid)* - **EDTA** is primarily used for **lead poisoning** and hypercalcemia. - While not routinely used for iron poisoning, it can form iron-EDTA complexes, which may paradoxically worsen toxicity. - **CaNa₂EDTA** is avoided in iron poisoning due to potential complications. *Desferrioxamine* - **Desferrioxamine (Deferoxamine)** is the **first-line antidote** for severe iron poisoning. - It is a highly specific iron-chelating agent that binds free iron in the bloodstream and promotes its renal excretion as ferrioxamine. - It reduces iron-mediated oxidative damage to organs (especially liver, heart, and GI tract). *Gastric lavage* - **Gastric lavage** can be used as a decontamination method in acute iron poisoning if performed early (within 1-2 hours of ingestion). - It helps remove unabsorbed iron tablets from the stomach, reducing further systemic absorption. - Whole bowel irrigation with polyethylene glycol is often preferred for iron tablet ingestion.

Question 700: All are features of organophosphorus poisoning, except:

A. Lacrimation
B. Bradycardia
C. Sweating
D. Mydriasis (Correct Answer)

Explanation: ***Mydriasis*** - Organophosphorus poisoning leads to excessive **acetylcholine** activity, causing **miosis** (pinpoint pupils), not mydriasis. - Mydriasis would indicate **anticholinergic** effects, which are opposite to the symptoms of organophosphorus poisoning. *Lacrimation* - Excess **acetylcholine** stimulates **muscarinic receptors** in lacrimal glands, leading to excessive tear production. - This is a classic "SLUDGE" symptom (Salivation, Lacrimation, Urination, Defecation, Gastric upset, Emesis). *Bradycardia* - Increased **acetylcholine** activity at cardiac muscarinic receptors (M2 receptors) slows the heart rate, causing **bradycardia**. - This is a common and potentially dangerous cardiovascular effect of organophosphorus poisoning. *Sweating* - **Acetylcholine** acts on muscarinic receptors in secretory glands, including sweat glands, causing profuse **sweating**. - This is another characteristic cholinergic symptom due to widespread autonomic overstimulation.

Practice by Chapter

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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