Clinical Pharmacology and Drug Toxicity — MCQs

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

Question 871: In cases of poisoning, which substance is most effectively treated with alkaline diuresis?

A. Benzodiazepine
B. Barbiturates (Correct Answer)
C. Dhatura
D. Morphine

Explanation: Correct: Barbiturates - **Alkaline diuresis** is highly effective for barbiturate poisoning because barbiturates are **weak acids** (pKa 7.2-8.5). - By alkalizing the urine (e.g., with **sodium bicarbonate** to pH 7.5-8.0), the drug becomes **ionized**, preventing its reabsorption in the renal tubules and promoting urinary excretion. - This is particularly effective for **long-acting barbiturates** like phenobarbital. *Incorrect: Benzodiazepine* - Benzodiazepines are generally **lipid-soluble** compounds and are extensively metabolized in the liver, primarily via **oxidation and glucuronidation**. - **Alkaline diuresis** is not an effective method for enhancing their elimination from the body. - The specific antidote is **flumazenil**, and treatment is primarily supportive [1]. *Incorrect: Dhatura* - **Dhatura poisoning** is caused by anticholinergic compounds (e.g., atropine, scopolamine) producing an anticholinergic toxidrome. - Management focuses on supportive care and the administration of **physostigmine** for severe anticholinergic symptoms. - **Alkaline diuresis** is not indicated for anticholinergic toxicity. *Incorrect: Morphine* - **Morphine** is an **opioid** that is primarily metabolized in the liver and excreted as glucuronide conjugates. - The specific antidote is **naloxone**, and treatment is primarily supportive. - **Alkaline diuresis** is not effective for enhancing morphine elimination, as opioids are not weak acids amenable to ion trapping.

Question 872: Which is the preferred antidote for methanol poisoning?

A. Flumazenil
B. Fomepizole (Correct Answer)
C. Naloxone
D. Ethanol

Explanation: ***Fomepizole*** - **Fomepizole** is a competitive inhibitor of **alcohol dehydrogenase**, the enzyme responsible for metabolizing methanol into toxic metabolites like formic acid. - By inhibiting this enzyme, it prevents the formation of toxic metabolites, thus reducing organ damage and metabolic acidosis. - **Fomepizole is the preferred first-line antidote** due to its easier dosing, absence of central nervous system depression, and less frequent monitoring requirements compared to ethanol. *Ethanol* - **Ethanol** also acts as a competitive inhibitor of **alcohol dehydrogenase**, similar to fomepizole, and is an effective alternative antidote. - However, it is now considered a **second-line option** when fomepizole is unavailable due to its disadvantages: difficult dosing requirements, CNS depression, need for frequent monitoring, and hypoglycemia risk. *Naloxone* - **Naloxone** is a specific opioid receptor antagonist used to reverse opioid overdose. - It has no role in the metabolism or detoxification of methanol poisoning. *Flumazenil* - **Flumazenil** is a benzodiazepine receptor antagonist used to reverse the effects of benzodiazepine overdose. - It does not have any therapeutic effect in cases of methanol poisoning.

Question 873: Methysergide is banned due to which serious side effect?

A. Syncope
B. Pleural effusion
C. Myocarditis
D. Pulmonary fibrosis (Correct Answer)

Explanation: ***Pulmonary fibrosis*** - Methysergide is a **serotonin antagonist** (specifically 5-HT₂) that was banned due to **serious fibrotic reactions**, which can affect multiple sites including the pleura, lungs, retroperitoneum, and heart valves. - **Pleuropulmonary fibrosis** (retropleural fibrosis) can lead to **restrictive lung disease** with impaired respiratory function, presenting as progressive dyspnea and chest pain. - While **retroperitoneal fibrosis** is the most common fibrotic complication, the broader spectrum of **fibrotic reactions** including pulmonary involvement led to the drug's withdrawal from most markets. - This is a serious and potentially life-threatening side effect that typically develops after prolonged use (usually >6 months). *Pleural effusion* - While pleural effusion can occur as a **secondary manifestation** of the underlying pleuropulmonary fibrosis, it is not the primary pathology. - The **fibrotic changes** themselves (not just the effusion) are the critical concern that led to the ban. - An isolated pleural effusion without fibrosis would not explain the drug's withdrawal. *Syncope* - **Syncope** (fainting) is not a recognized serious side effect of methysergide and was not responsible for its market withdrawal. - The drug's safety profile is dominated by **fibrotic complications**, not cardiovascular events like syncope. *Myocarditis* - **Myocarditis** (inflammation of the heart muscle) is not associated with methysergide use. - The cardiac complication related to methysergide is **endocardial and valvular fibrosis**, not inflammatory myocarditis. - This represents another manifestation of the drug's fibrotic side effect profile.

Question 874: Neuropsychiatric symptoms are seen with which anti-tuberculosis drug?

A. Rifampicin
B. Pyrazinamide
C. Streptomycin
D. Isoniazid (INH) (Correct Answer)

Explanation: ***Isoniazid (INH)*** - **Isoniazid** can cause **neuropsychiatric symptoms** due to its interference with **pyridoxine (vitamin B6)** metabolism, leading to a deficiency. - This deficiency can result in **peripheral neuropathy**, **optic neuritis**, seizures, psychosis, and cognitive impairment. *Rifampicin* - **Rifampicin** is associated with side effects such as **hepatotoxicity**, gastrointestinal disturbances, and a characteristic **orange discoloration of body fluids**. - It primarily affects the liver and GI tract but does not typically cause significant **neuropsychiatric symptoms**. *Pyrazinamide* - **Pyrazinamide** is known for causing **hyperuricemia** (leading to gouty arthritis) and **hepatotoxicity**. - While it can cause some central nervous system effects like headache, it is **not commonly associated with a broad range of neuropsychiatric symptoms** like INH. *Streptomycin* - **Streptomycin** is an aminoglycoside antibiotic primarily associated with **ototoxicity** (vestibular and auditory dysfunction) and **nephrotoxicity**. - Its side effect profile does not typically include **neuropsychiatric symptoms** as a prominent feature.

Question 875: Which of the following cephalosporins is most commonly associated with drug-induced thrombocytopenia?

A. Cefixime
B. Cefoperazone (Correct Answer)
C. Ceftazidime
D. Cefdinir

Explanation: ***Cefoperazone*** - **Cefoperazone** is most commonly associated with drug-induced thrombocytopenia among the listed cephalosporins. - It contains the **N-methylthiotetrazole (NMTT) side chain**, which is associated with two major hematological complications: - **Hypoprothrombinemia** due to interference with vitamin K metabolism (leading to bleeding) - **Immune-mediated thrombocytopenia** where the drug acts as a hapten, inducing antibody formation against platelets - Other cephalosporins with NMTT side chains (cefamandole, cefotetan, moxalactam) share similar risks. - The dual mechanism of both coagulation factor depletion and platelet destruction makes cefoperazone particularly notable for hematological adverse effects. *Ceftazidime* - **Ceftazidime** is a third-generation cephalosporin that can rarely cause thrombocytopenia through immune-mediated mechanisms. - However, the incidence is **lower compared to cefoperazone** and it lacks the NMTT side chain. - Reports exist but it is not the "most commonly associated" among cephalosporins. *Cefixime* - **Cefixime** is an oral third-generation cephalosporin with a **very low risk** of hematological side effects. - Reports of cefixime-induced thrombocytopenia are **exceedingly rare** and not commonly cited in pharmacology literature. *Cefdinir* - **Cefdinir** is an oral third-generation cephalosporin used for common bacterial infections. - Like cefixime, reports of **cefdinir-induced thrombocytopenia** are extremely rare and not a recognized common adverse effect.

Question 876: A patient with recurrent gout attacks was started on a drug that inhibits uric acid synthesis. His symptoms were reduced after therapy. Which drug was he started on?

A. Probenecid
B. Colchicine
C. Diclofenac
D. Allopurinol (Correct Answer)

Explanation: ***Allopurinol*** - **Allopurinol** is a **xanthine oxidase inhibitor** that effectively reduces uric acid synthesis by blocking the enzyme responsible for converting hypoxanthine and xanthine to uric acid. - It is a cornerstone therapy for preventing recurrent gout attacks in patients with **hyperuricemia**. *Probenecid* - **Probenecid** is a **uricosuric agent** that increases the excretion of uric acid in the urine, rather than inhibiting its synthesis. - It works by inhibiting the reabsorption of uric acid in the renal tubules. *Colchicine* - **Colchicine** is an **anti-inflammatory agent** primarily used to treat acute gout flares and prevent future attacks by disrupting microtubule function and inhibiting neutrophil migration. - It does not affect uric acid synthesis or excretion. *Diclofenac* - **Diclofenac** is a **non-steroidal anti-inflammatory drug (NSAID)** used to manage the pain and inflammation associated with acute gout attacks. - It works by inhibiting prostaglandin synthesis and has no effect on uric acid levels.

Question 877: Patient with pulmonary fibrosis. Which antiarrhythmic drug is contraindicated?

A. Amiodarone (Correct Answer)
B. Flecainide
C. Lidocaine
D. IV ibutilide

Explanation: Amiodarone - **Amiodarone** is contraindicated in patients with pulmonary fibrosis due to its well-known and potentially severe pulmonary toxicity, which can exacerbate existing lung conditions or induce new ones like **interstitial lung disease**. Dose-related pulmonary toxicity is the most important adverse effect, and potentially fatal pulmonary fibrosis can be observed even at low doses [1]. - Its long half-life means that its toxic effects, including **pulmonary toxicity**, can persist for an extended period even after discontinuation [1], [2]. *Flecainide* - **Flecainide** is a Class IC antiarrhythmic drug primarily associated with cardiac side effects and is generally not contraindicated in patients with pulmonary fibrosis. - Its main risks include **proarrhythmia**, especially in patients with structural heart disease, but not pulmonary issues [3]. *IV ibutilide* - **IV ibutilide** is a Class III antiarrhythmic agent used for rapid conversion of atrial fibrillation/flutter and is not specifically contraindicated in pulmonary fibrosis. - Its primary concern is the risk of **QT prolongation** and **Torsades de Pointes**, rather than pulmonary complications. *Lidocaine* - **Lidocaine** is a Class IB antiarrhythmic typically used for ventricular arrhythmias, especially in the setting of acute myocardial infarction. It is not contraindicated in pulmonary fibrosis. - Its main side effects are **neurological (e.g., seizures, paresthesias)** at higher doses, not pulmonary complications.

Question 878: A patient with diabetes and COPD developed postoperative urinary retention. Considering the patient's condition, which of the following drugs can be used for short-term treatment to relieve the symptoms?

A. Bethanechol
B. Methacholine
C. Tamsulosin (Correct Answer)
D. Terazosin

Explanation: ***Tamsulosin*** - **Tamsulosin** is a **selective α1A-adrenergic antagonist** that is the most appropriate choice for postoperative urinary retention in this patient with COPD and diabetes. - It relaxes smooth muscle in the **bladder neck and prostatic urethra**, relieving bladder outlet obstruction without affecting respiratory function. - Its **uroselective properties** minimize systemic side effects like hypotension, making it safer in diabetic patients who may have autonomic dysfunction. - **Safe in COPD** as it has no bronchoconstrictive effects and does not affect glucose metabolism. *Bethanechol* - **Bethanechol** is a direct-acting muscarinic agonist that stimulates bladder detrusor muscle contraction. - However, it is **relatively contraindicated in COPD** due to its potential to cause **bronchospasm** and increase bronchial secretions through M3 receptor stimulation in the airways. - The risk of respiratory complications in a COPD patient outweighs its benefits for urinary retention. - Modern practice rarely uses bethanechol for urinary retention due to safety concerns and availability of safer alternatives. *Methacholine* - **Methacholine** is a non-selective muscarinic agonist used primarily for **bronchial provocation testing** to diagnose asthma and airway hyperreactivity. - It causes significant **bronchospasm** and is absolutely contraindicated in COPD patients. - Not used therapeutically for urinary retention due to severe systemic cholinergic side effects. *Terazosin* - **Terazosin** is a non-selective **α1-adrenergic antagonist** used for benign prostatic hyperplasia and hypertension. - While effective for bladder outlet obstruction, it causes more **orthostatic hypotension** than tamsulosin due to its non-selective α1 blockade. - In diabetic patients with potential **autonomic neuropathy**, the risk of postural hypotension makes it less preferable than the more selective tamsulosin.

Question 879: A patient diagnosed with Rheumatoid arthritis was on medications. After 2 years, he developed a blurring vision and was found to have corneal opacity. Which drug is most likely to cause this?

A. Sulfasalazine
B. Leflunomide
C. Chloroquine (Correct Answer)
D. Methotrexate

Explanation: ***Chloroquine*** - **Chloroquine (and hydroxychloroquine)** can accumulate in the **cornea**, leading to **corneal opacity** (vortex keratopathy or cornea verticillata) and **retinopathy**, manifesting as blurring vision. - While corneal changes are usually reversible upon discontinuation, the retinal toxicity, particularly **maculopathy** (bull's eye maculopathy), can be permanent and severe. *Sulfasalazine* - Common side effects include **gastrointestinal upset**, headache, skin rash, and **bone marrow suppression**. - It is not typically associated with **corneal opacity** or significant ocular toxicity. *Leflunomide* - Known for side effects such as **hepatotoxicity**, gastrointestinal issues (diarrhea), **alopecia**, and **hypertension**. - **Ocular side effects** like corneal opacity are not characteristic of leflunomide use. *Methotrexate* - Primary side effects include **bone marrow suppression**, **hepatotoxicity**, **mucositis**, and **pulmonary fibrosis**. - Although it can cause ocular side effects like **conjunctivitis**, it is not a common cause of **corneal opacity**.

Question 880: Which fluoroquinolone is contraindicated in patients with liver disease?

A. Ofloxacin
B. Lomefloxacin
C. Levofloxacin
D. Pefloxacin (Correct Answer)

Explanation: ***Pefloxacin*** - **Pefloxacin** is primarily metabolized by the **liver**, and its accumulation due to hepatic impairment can lead to increased toxicity and adverse effects, making it contraindicated. - Patients with **severe liver disease** are at a higher risk of experiencing elevated drug levels, leading to complications like **tendinopathy**, **CNS side effects**, or **hepatotoxicity**. *Levofloxacin* - **Levofloxacin** is predominantly excreted by the **kidneys** and only minimally metabolized by the liver, making it generally safer in patients with hepatic impairment. - While dose adjustments may be necessary in **renal dysfunction**, liver disease typically does not require significant modifications. *Ofloxacin* - **Ofloxacin** elimination is primarily **renal**, with little hepatic metabolism, thus it is generally considered safe for use in patients with liver disease. - It does not undergo extensive biotransformation in the liver, minimizing the risk of accumulation in individuals with impaired hepatic function. *Lomefloxacin* - **Lomefloxacin** is relatively safe in patients with liver disease as it is predominantly eliminated renally, similar to levofloxacin and ofloxacin. - Its metabolic pathway does not involve significant hepatic processing, reducing the concern for toxicity in individuals with compromised liver function.

Practice by Chapter

Principles of Clinical Pharmacology

Practice Questions

Therapeutic Drug Monitoring

Practice Questions

Drug Toxicity and Overdose

Practice Questions

Antidotes and Their Applications

Practice Questions

Management of Drug Poisoning

Practice Questions

Drug-Induced Liver Injury

Practice Questions

Drug-Induced Kidney Injury

Practice Questions

Drug-Induced Blood Dyscrasias

Practice Questions

Drug-Induced QT Prolongation

Practice Questions

Pharmacovigilance

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free