Clinical Pharmacology and Drug Toxicity — MCQs

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

Question 1021: Which of the following is not a recommended treatment for lithium toxicity?

A. Increased hydration
B. Acidification of urine (Correct Answer)
C. Hemodialysis
D. Sodium bicarbonate

Explanation: ***Acidification of urine*** - **Lithium** is primarily excreted by the kidneys unchanged, and its renal handling is influenced by sodium and water balance, not urinary pH changes. - Urinary acidification is effective for enhancing elimination of **weak bases** (e.g., amphetamines), but lithium is **not ionizable** and its excretion is pH-independent. - This intervention is **ineffective for lithium toxicity** and could potentially worsen electrolyte imbalances. *Increased hydration* - **Increased hydration** with intravenous normal saline is a cornerstone of lithium toxicity management. - Saline infusion helps to **restore intravascular volume**, improve GFR, and reduce proximal tubular reabsorption of lithium (lithium is reabsorbed along with sodium) [1]. - This intervention effectively **lowers serum lithium levels** in mild-to-moderate toxicity. *Sodium bicarbonate* - **Sodium bicarbonate** is NOT a standard treatment for lithium toxicity. - Unlike drugs eliminated by ion trapping (salicylates, methotrexate), lithium excretion is **not enhanced by urinary alkalinization**. - While sodium administration (via saline) helps lithium excretion, the bicarbonate component provides no additional benefit over normal saline and may cause metabolic alkalosis. - Sodium bicarbonate may be used if metabolic **acidosis** is present as a complication, but not as a primary treatment for lithium toxicity itself. *Hemodialysis* - **Hemodialysis** is the most effective and definitive treatment for severe lithium toxicity (serum levels >4 mEq/L, severe symptoms, renal failure, or deteriorating clinical status). - Lithium has ideal characteristics for dialysis: **low molecular weight** (7 Da), minimal protein binding (<10%), and small volume of distribution (0.7-0.9 L/kg). - Can rapidly reduce serum lithium levels by **50% or more** per session.

Question 1022: Belimumab is used in

A. Osteoporosis
B. Malignant melanoma
C. Merkel cell carcinoma
D. Systemic lupus erythematosus (Correct Answer)

Explanation: ***Systemic lupus erythematosus*** - **Belimumab** is a monoclonal antibody that targets and inhibits **B-cell activating factor (BAFF)**, reducing the survival of autoreactive B cells. - This medication is FDA-approved for the treatment of **active systemic lupus erythematosus (SLE)** in patients who are receiving standard therapy. *Osteoporosis* - **Osteoporosis** is primarily treated with bisphosphonates, denosumab, teriparatide, or romosozumab, which focus on bone density and remodeling. - Belimumab has **no direct mechanism of action** for increasing bone mass or preventing bone resorption. *Malignant melanoma* - **Malignant melanoma** is typically treated with surgical excision, targeted therapies (e.g., BRAF/MEK inhibitors), or immunotherapies (e.g., PD-1 or CTLA-4 inhibitors). - Belimumab's mechanism of action, targeting B-cell activating factor, is **not relevant to the treatment of melanoma**. *Merkel cell carcinoma* - **Merkel cell carcinoma** is a rare and aggressive skin cancer primarily treated with surgery, radiation, and immunotherapy, particularly PD-1 inhibitors like avelumab. - Belimumab's role in modulating B-cell activity **does not apply to the pathogenesis or treatment of Merkel cell carcinoma**.

Question 1023: Sterile pyuria may occur due to:

A. Cocaine
B. Lignocaine
C. Paracetamol
D. Phenytoin (Correct Answer)

Explanation: ***Phenytoin*** - **Phenytoin** is a well-known cause of **drug-induced acute interstitial nephritis (AIN)**, which is a classic cause of **sterile pyuria**. - **Acute interstitial nephritis** presents with inflammatory infiltration of the renal interstitium, leading to pyuria (white blood cells in urine) **without bacterial infection**. - Other features of drug-induced AIN include fever, rash, eosinophilia, and acute kidney injury. - Phenytoin, along with other drugs like penicillins, NSAIDs, and rifampicin, can trigger this hypersensitivity-mediated renal injury. *Paracetamol* - **Paracetamol (acetaminophen)** overdose causes **acute tubular necrosis (ATN)**, not interstitial nephritis. - ATN primarily presents with acute kidney injury, oliguria, and elevated creatinine, but **sterile pyuria is not a characteristic feature** of ATN. - The renal damage is direct tubular cell injury rather than inflammatory interstitial infiltration. *Lignocaine* - **Lignocaine (lidocaine)** is a local anesthetic and antiarrhythmic agent with side effects primarily affecting the **central nervous system and cardiovascular system**. - It is **not associated with renal toxicity** or sterile pyuria. *Cocaine* - **Cocaine** can cause kidney damage through **rhabdomyolysis**, **vasoconstriction**, and **hypertensive crisis**, leading to **acute kidney injury**. - While cocaine-related AKI can occur, it does not typically cause **drug-induced interstitial nephritis** or classic sterile pyuria. - Renal injury from cocaine is usually related to ischemic or myoglobinuric mechanisms rather than inflammatory infiltration.

Question 1024: Which one of the following nonsteroidal anti-inflammatory drugs has adverse effects on the liver?

A. Aspirin
B. Ibuprofen
C. Diclofenac Sodium (Correct Answer)
D. Naproxen

Explanation: ***Diclofenac Sodium*** - **Diclofenac** is the NSAID most commonly associated with **hepatotoxicity** among commonly prescribed NSAIDs - Can cause **elevated liver enzymes** (transaminases) and in rare cases **severe hepatotoxicity** leading to acute liver failure - Has **black box warnings** in many countries regarding hepatic adverse effects - **Regular monitoring of liver function tests** is recommended for patients on long-term diclofenac therapy - Hepatotoxicity risk is dose-dependent and more common with prolonged use *Aspirin* - Aspirin (acetylsalicylic acid) is an NSAID with primary adverse effects related to **gastrointestinal irritation**, **bleeding**, and **antiplatelet effects** - In children, associated with **Reye's syndrome** (hepatic encephalopathy) - Very high doses or chronic use can cause mild, reversible liver enzyme elevations, but **significant hepatotoxicity is uncommon** in adults - Not prominently associated with liver toxicity compared to diclofenac *Ibuprofen* - Ibuprofen is a well-tolerated NSAID with most common adverse effects being **gastrointestinal discomfort**, **peptic ulcers**, and **renal impairment** - Although NSAIDs as a class can rarely cause idiosyncratic liver injury, ibuprofen has a **very low incidence of hepatotoxicity** - Considered one of the safer NSAIDs regarding hepatic effects *Naproxen* - Naproxen is a commonly used NSAID with primary adverse effects similar to other NSAIDs: **gastrointestinal irritation** and **renal effects** - Hepatotoxicity is **rare** with naproxen compared to diclofenac - Generally well-tolerated with respect to liver function - Idiosyncratic liver injury can occur but is uncommon

Question 1025: Constipation is a possible side effect of drugs taken by the oral route. Which of the following medications is least likely to cause constipation?

A. promethazine
B. loperamide
C. docusate (Correct Answer)
D. diphenhydramine

Explanation: ***docusate*** - **Docusate** is a **stool softener** and is actually used to prevent and treat constipation, making it the least likely to cause it. - It works by increasing the amount of water and fat the stool absorbs, making it easier to pass. *promethazine* - **Promethazine** is an antihistamine with **anticholinergic properties** that can slow down gut motility. - Reduced gastrointestinal motility is a common side effect of drugs with anticholinergic effects, leading to **constipation**. *loperamide* - **Loperamide** is an **opioid receptor agonist** that works by slowing down gut contractions. - It is specifically used as an **antidiarrheal medication**, and constipation is a well-known side effect of its action. *diphenhydramine* - **Diphenhydramine** is an antihistamine with significant **anticholinergic effects**. - Its anticholinergic action reduces intestinal motility and secretions, frequently causing **constipation**.

Question 1026: A woman consumes several tablets of amitriptyline (a case of amitriptyline poisoning). Which of the following is NOT an appropriate management step?

A. Gastric lavage
B. Atropine as antidote (Correct Answer)
C. Sodium bicarbonate infusion
D. Activated charcoal administration

Explanation: ***Atropine as antidote*** - **Atropine** is primarily used to counteract **cholinergic toxicity** (e.g., organophosphate poisoning), while amitriptyline causes **anticholinergic effects**. Administering atropine would worsen the patient's condition by exacerbating these effects (tachycardia, hyperthermia, delirium, urinary retention). - The main toxic effects of amitriptyline are related to its impact on cardiac conduction (sodium channel blockade), central nervous system depression, and profound anticholinergic actions, none of which are reversed by atropine. *Sodium bicarbonate infusion* - **Sodium bicarbonate** is the **gold standard treatment** for **QRS widening >100 ms** and **ventricular arrhythmias** caused by amitriptyline. - It increases extracellular sodium concentration and alkalinizes the plasma, which helps to overcome the **sodium channel blockade** and reduces TCA binding to cardiac sodium channels. - Bolus dosing (1-2 mEq/kg) followed by infusion to maintain alkaline pH (7.45-7.55) is recommended. *Gastric lavage* - **Gastric lavage is NOT routinely recommended** in modern toxicology practice for amitriptyline poisoning due to **limited efficacy** and **significant risks** (aspiration, especially with CNS depression). - Current evidence shows **no improvement in clinical outcomes** and potential for harm. - While historically mentioned as an option for recent, massive ingestions, it has been largely abandoned in favor of activated charcoal, making this a questionable management step in contemporary practice. *Activated charcoal administration* - **Activated charcoal** is the **preferred decontamination method** to reduce absorption of amitriptyline from the gastrointestinal tract. - It has a **large surface area** and effectively binds TCAs, preventing systemic absorption. - Most effective when administered within **1-2 hours** of ingestion; single dose of 1 g/kg (usually 25-50 g in adults) is recommended if airway is protected.

Question 1027: Methemoglobinemia is associated with:

A. Aminoester local anesthetic
B. Prilocaine (Correct Answer)
C. Bupivacaine
D. Mepivacaine

Explanation: ***Prilocaine*** - **Prilocaine** is a local anesthetic known to cause **methemoglobinemia** at higher doses due to its metabolite, **o-toluidine**. - This metabolite oxidizes iron in hemoglobin from the ferrous (Fe2+) to the ferric (Fe3+) state, rendering it unable to bind oxygen. *Aminoester local anesthetic* - While some aminoester local anesthetics can cause allergic reactions, they are not typically associated with **methemoglobinemia**. - **Methemoglobinemia** is more commonly linked with aminoamide local anesthetics containing specific chemical structures. *Bupivacaine* - **Bupivacaine** is an aminoamide local anesthetic primarily known for its potential to cause **cardiotoxicity** at high systemic concentrations. - It does not commonly induce **methemoglobinemia**. *Mepivacaine* - **Mepivacaine** is another aminoamide local anesthetic, chemically similar to lidocaine. - While it can cause CNS toxicity and cardiovascular effects at high doses, it is not a significant cause of **methemoglobinemia**.

Question 1028: What is the cause of cough and angioedema in a patient receiving ACE inhibitors?

A. Bradykinin
B. Increased renin levels
C. Increased angiotensin-II levels
D. Bradykinin accumulation (Correct Answer)

Explanation: ***Bradykinin accumulation*** - **ACE inhibitors** block the enzyme **angiotensin-converting enzyme (ACE)**, which is responsible for degrading **bradykinin**. - The resulting **accumulation of bradykinin** is a potent vasodilator and increases capillary permeability, leading to **cough** (5-20% of patients) and **angioedema** (0.1-0.7%). - This is the most **precise answer** as it specifies the mechanism: impaired degradation leading to accumulation. *Bradykinin (alone)* - While **bradykinin** is the mediator involved, this option is **less precise** than "bradykinin accumulation." - **Bradykinin** is naturally present in the body; the problem with ACE inhibitors is specifically the **accumulation** due to impaired degradation. - The correct answer requires understanding that it's the **excess levels**, not just the presence, that causes symptoms. *Increased renin levels* - **ACE inhibitors** block the conversion of **angiotensin I to angiotensin II**, leading to reduced negative feedback. - This causes **compensatory increase in renin secretion** from the juxtaglomerular apparatus. - However, increased renin is **not responsible** for cough or angioedema—these are bradykinin-mediated effects. *Increased angiotensin-II levels* - **ACE inhibitors** actually **decrease angiotensin-II levels**, which is their primary **antihypertensive mechanism**. - This option is **incorrect** as ACE inhibitors reduce (not increase) angiotensin-II. - The reduction in angiotensin-II does not cause cough or angioedema.

Question 1029: Which of the following antidepressants causes urine retention?

A. Imipramine (Correct Answer)
B. Sertraline
C. Bupropion
D. Fluoxetine (Prozac)

Explanation: ***Imipramine*** - Imipramine is a **tricyclic antidepressant (TCA)** with potent **anticholinergic effects** [1] - **Anticholinergic activity** blocks muscarinic receptors in the bladder, causing **urinary retention** by relaxing the detrusor muscle and increasing urethral sphincter tone [1] - TCAs are well-known for causing anticholinergic side effects including dry mouth, constipation, blurred vision, and urinary retention [1] *Fluoxetine (Prozac)* - Fluoxetine is a **selective serotonin reuptake inhibitor (SSRI)** [1] - SSRIs have **minimal anticholinergic activity** and are not typically associated with urinary retention [1] - Side effects are primarily serotonergic (nausea, sexual dysfunction, insomnia) *Bupropion* - Bupropion is a **norepinephrine-dopamine reuptake inhibitor (NDRI)** - Has **minimal anticholinergic effects** and does not typically cause urinary retention - Common side effects include insomnia, agitation, and seizure risk at high doses *Sertraline* - Sertraline is another **selective serotonin reuptake inhibitor (SSRI)** [1] - Like fluoxetine, sertraline has **minimal anticholinergic activity** [1] - Not associated with urinary retention or other anticholinergic side effects

Question 1030: Which one of the following can cause agranulocytosis most commonly?

A. Alkylating agents (Correct Answer)
B. Paracetamol
C. Endotoxemia
D. Corticosteroids

Explanation: ***Alkylating agents*** - Among the given options, alkylating agents are the **most likely to cause severe neutropenia/agranulocytosis** due to their mechanism of action. - These chemotherapeutic drugs **directly damage bone marrow stem cells**, causing dose-dependent **myelosuppression** affecting all cell lines, including severe reduction in neutrophil production. - Their mechanism involves **cross-linking DNA and interfering with DNA replication**, which is particularly detrimental to rapidly dividing hematopoietic cells. - **Clinical note:** While classic drug-induced agranulocytosis is more associated with drugs like clozapine, carbamazepine, or antithyroid medications, alkylating agents cause the most severe and predictable bone marrow suppression among these options. *Corticosteroids* - Corticosteroids cause **leukocytosis** (increased white blood cells), not agranulocytosis. - They work by **demarginating neutrophils** from vessel walls and decreasing their migration into tissues. - They may suppress lymphocytes and eosinophils but do **not cause agranulocytosis**. *Paracetamol* - Paracetamol is **not associated with agranulocytosis** as a recognized adverse effect. - Its primary toxicity concern is **dose-dependent hepatotoxicity** due to glutathione depletion and formation of toxic metabolite NAPQI. - Hematological adverse effects are extremely rare. *Endotoxemia* - Endotoxemia (associated with gram-negative bacterial sepsis) typically causes **leukocytosis with left shift** (increased immature neutrophils). - The body mounts an immune response with **neutrophil activation and release**, not suppression. - While severe prolonged sepsis can affect bone marrow, the typical response is increased, not decreased, neutrophil count.

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