Clinical Pharmacology and Drug Toxicity Practice Questions

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

Barbiturates. 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.

Q: Methysergide is banned due to which serious side effect?

Pulmonary fibrosis. ***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.

Q: Which is the preferred antidote for methanol poisoning?

Fomepizole. ***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.

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

Cefoperazone. ***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.

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

Isoniazid (INH). ***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.

Q: 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?

Allopurinol. ***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.

Q: 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?

Chloroquine. ***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**.

Q: Which of the following vitamins, when taken at higher doses, can cause cystoid macular edema?

Niacin. ***Niacin*** - High doses of **niacin (nicotinic acid)**, particularly the extended-release forms used for lipid management, are known to cause **cystoid macular edema (CME)**. - The mechanism is thought to involve **vasodilation** and metabolic changes in the retinal pigment epithelium. *Vitamin A* - While essential for vision, **excessive vitamin A** intake (hypervitaminosis A) can lead to symptoms like **headache**, **blurred vision**, and skin changes, but not typically cystoid macular edema. - Deficiency of vitamin A can cause **night blindness** and xerophthalmia. *Vitamin D* - High doses of vitamin D can lead to **hypercalcemia**, causing symptoms such as nausea, vomiting, and kidney stones. - It does not directly cause **cystoid macular edema**. *Vitamin E* - **Excessive vitamin E** intake can interfere with **blood clotting** and increase the risk of bleeding, especially in individuals on anticoagulants. - There is no established link between high-dose vitamin E and **cystoid macular edema**.

Q: MgSO4 has no role in the prevention of...

Bradycardia. ***Bradycardia*** - Magnesium sulfate has **no role in preventing bradycardia**; in fact, it can **cause or worsen bradycardia** as a significant side effect. - MgSO4 acts as a **calcium channel blocker** and CNS depressant, which can lead to cardiac conduction depression and bradycardia. - Its administration requires careful monitoring for cardiorespiratory depression, including bradycardia. *Seizures in severe pre-eclampsia* - Magnesium sulfate is the **drug of choice** for prevention of eclamptic seizures in women with severe pre-eclampsia (Magpie Trial). - It acts as a **CNS depressant** by reducing acetylcholine release at the neuromuscular junction and inhibiting neuronal excitability. - Clear established role in seizure prophylaxis. *Recurrent seizures in eclampsia* - Magnesium sulfate is the **gold standard** for treatment of active eclamptic seizures and prevention of their recurrence. - Its **anticonvulsant properties** make it the first-line agent in managing this life-threatening complication of pregnancy. - Superior to other anticonvulsants like diazepam or phenytoin in this context. *Respiratory Distress Syndrome (RDS) in premature baby* - **Antenatal corticosteroids** (betamethasone/dexamethasone), NOT magnesium sulfate, are used for **prevention of RDS** in premature babies. - While MgSO4 given antenatally does provide **neuroprotection** and reduces risk of cerebral palsy in preterm infants, this is distinct from RDS prevention. - MgSO4 has no established role in preventing respiratory distress syndrome itself.

Q: 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?

Tamsulosin. ***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 1

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

Accepted Answer

Barbiturates

Answer

Benzodiazepine

Answer

Dhatura

Answer

Morphine

Question 2

Methysergide is banned due to which serious side effect?

Accepted Answer

Pulmonary fibrosis

Answer

Syncope

Answer

Pleural effusion

Answer

Myocarditis

Question 3

Which is the preferred antidote for methanol poisoning?

Accepted Answer

Fomepizole

Answer

Flumazenil

Answer

Naloxone

Answer

Ethanol

Question 4

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

Accepted Answer

Cefoperazone

Answer

Cefixime

Answer

Ceftazidime

Answer

Cefdinir

Question 5

Neuropsychiatric symptoms are seen with which anti-tuberculosis drug?

Accepted Answer

Isoniazid (INH)

Answer

Rifampicin

Answer

Pyrazinamide

Answer

Streptomycin

Question 6

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?

Accepted Answer

Allopurinol

Answer

Probenecid

Answer

Colchicine

Answer

Diclofenac

Question 7

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?

Accepted Answer

Chloroquine

Answer

Sulfasalazine

Answer

Leflunomide

Answer

Methotrexate

Question 8

Which of the following vitamins, when taken at higher doses, can cause cystoid macular edema?

Accepted Answer

Niacin

Answer

Vitamin A

Answer

Vitamin D

Answer

Vitamin E

Question 9

MgSO4 has no role in the prevention of...

Accepted Answer

Bradycardia

Answer

Seizures in severe pre-eclampsia

Answer

Recurrent seizures in eclampsia

Answer

Respiratory Distress Syndrome (RDS) in premature baby

Question 10

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?

Accepted Answer

Tamsulosin

Answer

Bethanechol

Answer

Methacholine

Answer

Terazosin

Clinical Pharmacology and Drug Toxicity — MCQs

Clinical Pharmacology and Drug Toxicity — MCQs

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