Quinolones — MCQs
A patient is taking metronidazole for anaerobic infection. Which of the following should be avoided during this period
Which of the following drugs act by inhibiting DNA replication?
All of the following are adverse effects of thalidomide except:
Which one of the following antibiotic is not recommended for lactating mothers?
A woman presenting with symptoms of urinary tract infection was prescribed a drug that causes tendon rupture and arthropathy. What is the mechanism of action of the drug?
A 75-year-old male on warfarin is prescribed an antibiotic for pneumonia. Which antibiotic requires INR monitoring due to increased bleeding risk?
Mechanism of action of Pemetrexed is:-
Which antimicrobial inhibits cell wall synthesis?
Production of inactivating enzymes is an important mechanism of drug resistance for all of these antibiotics EXCEPT
On chronic use, linezolid leads to which of the following?
Quinolones Indian Medical PG Practice Questions and MCQs
Question 1: A patient is taking metronidazole for anaerobic infection. Which of the following should be avoided during this period
- A. Colchicine
- B. Alcohol (Correct Answer)
- C. Rifampicin
- D. Ciprofloxacin
- E. Warfarin
Explanation: ***Alcohol*** - Metronidazole inhibits **aldehyde dehydrogenase**, an enzyme responsible for metabolizing alcohol, leading to an accumulation of **acetaldehyde**. - This accumulation causes a **disulfiram-like reaction**, characterized by flushing, nausea, vomiting, headache, and palpitations, making alcohol avoidance crucial. *Colchicine* - Colchicine is used for gout and **familial Mediterranean fever**; there's no major contraindicated interaction with metronidazole. - While both can cause gastrointestinal side effects, combining them does not typically lead to a life-threatening interaction or necessitate avoidance. *Rifampicin* - Rifampicin is a potent **CYP450 enzyme inducer** and can decrease the effectiveness of many drugs, including metronidazole, by increasing its metabolism. - While an interaction exists, it typically involves reduced metronidazole efficacy rather than a strict contraindication requiring complete avoidance. *Ciprofloxacin* - Ciprofloxacin is a **quinolone antibiotic** and generally does not have a clinically significant, contraindicated interaction with metronidazole. - Both can individually cause **gastrointestinal side effects**, but their co-administration is not generally discouraged due to synergy in treatment or increased toxicity. *Warfarin* - Metronidazole can enhance the anticoagulant effect of warfarin by inhibiting its metabolism, potentially increasing **INR** and bleeding risk. - However, this interaction is **manageable with monitoring**; warfarin is not absolutely contraindicated and can be used with dose adjustments and frequent INR checks, unlike alcohol which must be completely avoided.
Question 2: Which of the following drugs act by inhibiting DNA replication?
- A. Mitomycin C
- B. 6-Mercaptopurine (Correct Answer)
- C. Actinomycin D
- D. Asparaginase
Explanation: ***6-Mercaptopurine*** - This drug is a **purine analog** that acts as an **antimetabolite**, directly interfering with the **synthesis of purine nucleotides** required for DNA replication. - By inhibiting enzymes like **PRPP amidotransferase** and getting incorporated into DNA as a fraudulent nucleotide, it blocks the **de novo synthesis** pathway, preventing normal DNA replication. - This represents **direct inhibition of DNA synthesis** at the nucleotide building block level. *Mitomycin C* - This agent is an **alkylating agent** that **cross-links DNA** strands, causing DNA damage that prevents strand separation. - While it does prevent DNA replication, its mechanism is through **DNA damage and structural disruption** rather than inhibition of the DNA synthesis machinery itself. - It acts by damaging already-formed DNA rather than preventing new DNA synthesis. *Actinomycin D* - Actinomycin D is an **intercalating agent** that inserts itself between DNA base pairs, primarily **inhibiting RNA synthesis** by blocking RNA polymerase movement. - While it binds to DNA, its primary therapeutic action is on **transcription (RNA synthesis)**, not direct inhibition of DNA replication. *Asparaginase* - Asparaginase is an enzyme that **depletes asparagine** from the blood, which is an essential amino acid for certain cancer cells (e.g., leukemic cells). - Its mechanism is to starve cancer cells of asparagine, leading to **inhibition of protein synthesis**, not DNA replication.
Question 3: All of the following are adverse effects of thalidomide except:
- A. Constipation
- B. Myocarditis (Correct Answer)
- C. Peripheral neuropathy
- D. Sedation
Explanation: ***Myocarditis*** - **Myocarditis** is not an established adverse effect of thalidomide in standard pharmacology references. - While thalidomide can cause cardiovascular effects such as **bradycardia** and **thromboembolic events**, direct myocardial inflammation is not a recognized complication. - This is the correct answer as it is NOT an adverse effect of thalidomide. *Constipation* - **Constipation** is a very common gastrointestinal side effect of thalidomide due to its **anticholinergic-like effects**. - Patients often require proactive management with laxatives to mitigate this side effect. *Peripheral neuropathy* - **Peripheral neuropathy** is the most significant and dose-limiting adverse effect of thalidomide, often presenting as **sensory deficits** in a stocking-glove distribution. - It can be **irreversible** and may necessitate discontinuation of the drug. - This is a major concern requiring regular monitoring during treatment. *Sedation* - **Sedation** and **drowsiness** are common adverse effects of thalidomide due to its **central nervous system depressant properties**. - This effect often leads to administration before bedtime to minimize impact on daily activities.
Question 4: Which one of the following antibiotic is not recommended for lactating mothers?
- A. Aminoglycoside
- B. Quinolones (Correct Answer)
- C. Cephalosporins
- D. Anti tubercular drugs
Explanation: ***Quinolones*** - **Quinolones** are generally **not recommended** for lactating mothers due to concerns about potential harm to the infant's developing **cartilage** and **joints**. - They have been associated with **arthropathies** and **tendinopathies** in animal studies and young patients, leading to caution in this population. *Aminoglycoside* - **Aminoglycosides** are typically considered **safe** in lactation because they have **poor oral absorption** by the infant, meaning very little drug reaches the infant's systemic circulation. - While they can be excreted into breast milk, the amount absorbed by the infant is usually **negligible**, reducing risk of toxicity. *Cephalosporins* - **Cephalosporins** are generally considered **safe** for lactating mothers as they are excreted into breast milk in **low concentrations** and have a good safety profile for infants. - Potential side effects in the infant are usually minor, such as **diarrhea** or **thrush**, and serious adverse events are rare. *Anti tubercular drugs* - Most **first-line anti-tubercular drugs** (e.g., isoniazid, rifampicin, ethambutol, pyrazinamide) are generally **considered compatible** with breastfeeding. - While they do pass into breast milk, the benefits of treating **maternal tuberculosis** and preventing transmission to the infant usually outweigh the theoretical risks.
Question 5: A woman presenting with symptoms of urinary tract infection was prescribed a drug that causes tendon rupture and arthropathy. What is the mechanism of action of the drug?
- A. Ribosomal inhibition
- B. Cell wall synthesis
- C. Inhibition of folic acid synthesis
- D. DNA gyrase inhibition (Correct Answer)
Explanation: ***DNA gyrase inhibition*** - The description of a drug causing **tendon rupture** and **arthropathy** in the context of a urinary tract infection (UTI) suggests a **fluoroquinolone**. - Fluoroquinolones exert their bactericidal effect by inhibiting **bacterial DNA gyrase** (also known as topoisomerase II) and **topoisomerase IV**, thereby preventing DNA replication and repair. *Ribosomal inhibition* - This mechanism is characteristic of antibiotics like **aminoglycosides**, **tetracyclines**, and **macrolides**. - While some of these can treat UTIs, they are not typically associated with **tendon rupture** or **arthropathy** as major side effects. *Cell wall synthesis* - This is the mechanism of action for **beta-lactam antibiotics** (e.g., penicillins, cephalosporins) and **vancomycin**. - These drugs are common for UTIs but do not cause **tendon rupture** or **arthropathy**. *Inhibition of folic acid synthesis* - This mechanism is used by **sulfonamides** and **trimethoprim**, often combined as trimethoprim-sulfamethoxazole. - While effective for UTIs, these drugs are not known to cause **tendon rupture** or **arthropathy**.
Question 6: A 75-year-old male on warfarin is prescribed an antibiotic for pneumonia. Which antibiotic requires INR monitoring due to increased bleeding risk?
- A. Ciprofloxacin (Correct Answer)
- B. Amoxicillin
- C. Clindamycin
- D. Azithromycin
Explanation: ***Ciprofloxacin*** - **Ciprofloxacin** and other fluoroquinolones can interact with **warfarin**, though the mechanism is **not well-established** and likely multifactorial (may involve gut flora disruption, protein binding displacement, or metabolic effects). - This interaction can lead to **increased INR** and bleeding risk, requiring close monitoring. - Among fluoroquinolones, the interaction is **less predictable** compared to some other antibiotics. *Amoxicillin* - **Amoxicillin** and other beta-lactam antibiotics can interact with warfarin through **gut flora disruption**, reducing vitamin K synthesis. - This can lead to increased INR, though the effect is generally **mild to moderate**. - Routine INR monitoring is typically sufficient without intensive monitoring. *Clindamycin* - **Clindamycin** has **minimal documented interaction** with warfarin. - It does not significantly affect warfarin metabolism or vitamin K synthesis. - Generally considered a **safer option** for patients on warfarin therapy. *Azithromycin* - **Azithromycin** is well-documented to **significantly increase INR** and bleeding risk in patients on warfarin. - The mechanism may involve **CYP3A4 effects** and other pharmacokinetic interactions. - **FDA warnings exist** regarding this interaction, and close INR monitoring is essential. - Note: While this option is also clinically significant, the question focuses on identifying ONE antibiotic requiring monitoring, with ciprofloxacin being the presented answer in this educational context.
Question 7: Mechanism of action of Pemetrexed is:-
- A. Topoisomerase inhibitor
- B. Dihydrofolate reductase inhibitor
- C. Dopamine agonist
- D. Thymidylate synthase inhibitor (Correct Answer)
Explanation: ***Thymidylate synthase inhibitor*** - **Pemetrexed** is a **multi-targeted antifolate agent** that primarily inhibits **thymidylate synthase (TS)**, the key enzyme responsible for synthesizing thymidine monophosphate, an essential building block for DNA synthesis. - While pemetrexed also inhibits **dihydrofolate reductase (DHFR)** and **glycinamide ribonucleotide formyltransferase (GARFT)**, its **primary and most clinically significant mechanism** is TS inhibition, making it particularly effective in mesothelioma and non-small cell lung cancer. - This multi-targeted action enhances its cytotoxic effects compared to single-target antifolates. *Dihydrofolate reductase inhibitor* - While pemetrexed does inhibit **DHFR** as part of its multi-targeted mechanism, this is a **secondary action**, not its primary mechanism. - Classical DHFR inhibitors include **methotrexate** and **trimethoprim**, which specifically target this enzyme. - In exam contexts, pemetrexed is best classified by its **primary target: thymidylate synthase**. *Topoisomerase inhibitor* - **Topoisomerase inhibitors** target enzymes that control DNA topology during replication and transcription. - Examples include **irinotecan** and **topotecan** (topoisomerase I inhibitors) and **etoposide** (topoisomerase II inhibitor). - This is not the mechanism of action for pemetrexed. *Dopamine agonist* - **Dopamine agonists** activate dopamine receptors and are used in neurological conditions like Parkinson's disease (e.g., **pramipexole**, **ropinirole**). - This mechanism is completely unrelated to anticancer agents and folate metabolism.
Question 8: Which antimicrobial inhibits cell wall synthesis?
- A. Metronidazole
- B. Azithromycin
- C. Vancomycin (Correct Answer)
- D. Ciprofloxacin
Explanation: ***Vancomycin*** - **Vancomycin** is a glycopeptide antibiotic that inhibits cell wall synthesis by binding to the **D-Ala-D-Ala** terminal of peptidoglycan precursors. - This binding prevents the **transpeptidation** and **transglycosylation** steps necessary for peptidoglycan chain elongation and cross-linking, ultimately weakening the bacterial cell wall and leading to bacterial lysis. *Metronidazole* - **Metronidazole** is an antimicrobial that works by forming **toxic free-radical metabolites** that damage bacterial **DNA**. - Its mechanism of action does not involve direct inhibition of cell wall synthesis. *Azithromycin* - **Azithromycin** is a macrolide antibiotic that inhibits bacterial protein synthesis by binding to the **50S ribosomal subunit**. - This binding prevents **peptide chain elongation**, thereby halting protein production, rather than affecting the cell wall. *Ciprofloxacin* - **Ciprofloxacin** is a fluoroquinolone antibiotic that inhibits bacterial **DNA replication** and repair. - It achieves this by targeting **DNA gyrase** (topoisomerase II) and **topoisomerase IV**, enzymes crucial for bacterial DNA handling, and thus does not act on the cell wall.
Question 9: Production of inactivating enzymes is an important mechanism of drug resistance for all of these antibiotics EXCEPT
- A. Quinolone (Correct Answer)
- B. Penicillin
- C. Chloramphenicol
- D. Aminoglycoside
Explanation: ***Quinolone*** - The primary mechanisms of resistance to **quinolones** involve mutations in the **gyrase** and **topoisomerase IV** enzymes or efflux pump overexpression, rather than enzymatic inactivation of the drug itself. - Unlike other antibiotic classes listed, quinolones are not typically susceptible to bacterial enzymes that degrade or modify their structure. *Penicillin* - **Penicillins** are highly susceptible to inactivation by **beta-lactamase enzymes**, which hydrolyze the beta-lactam ring, rendering the antibiotic ineffective. - This enzymatic degradation is a major mechanism of resistance developed by many bacterial species to penicillin and other beta-lactam antibiotics. *Chloramphenicol* - Resistance to **chloramphenicol** is primarily mediated by the enzyme **chloramphenicol acetyltransferase (CAT)**, which acetylates the drug, preventing its binding to the bacterial ribosome. - This enzymatic modification is a classic example of drug inactivation leading to resistance. *Aminoglycoside* - **Aminoglycosides** are frequently inactivated by a variety of **aminoglycoside-modifying enzymes (AMEs)**, such as acetyltransferases, phosphoryltransferases, and nucleotidyltransferases. - These enzymes add chemical moieties to the aminoglycoside molecule, preventing its binding to the bacterial ribosome and inhibiting protein synthesis.
Question 10: On chronic use, linezolid leads to which of the following?
- A. Thrombocytopenia (Correct Answer)
- B. Deranged LFT
- C. Nephrotoxicity
- D. Ototoxicity
Explanation: ***Thrombocytopenia*** - **Linezolid** is known to cause **myelosuppression**, particularly **thrombocytopenia**, with prolonged use (typically >2 weeks). - This adverse effect is usually **reversible** upon discontinuation of the drug. - This is the **most characteristic** and **dose-limiting** hematologic toxicity of chronic linezolid therapy. *Deranged LFT* - While **linezolid** can occasionally cause **elevated liver enzymes**, this is a **less common** adverse effect compared to myelosuppression. - **Thrombocytopenia** is far more characteristic of **chronic linezolid use** and is the primary concern requiring monitoring. - Hepatotoxicity with linezolid is typically mild and less dose-limiting than hematologic effects. *Nephrotoxicity* - **Linezolid** is generally considered to have a low risk of **nephrotoxicity** and does not typically cause significant kidney damage. - **Aminoglycosides** or **vancomycin** are examples of antibiotics more commonly associated with nephrotoxic effects. *Ototoxicity* - **Ototoxicity**, characterized by hearing loss or tinnitus, is not a common or recognized side effect of **linezolid** therapy. - This adverse effect is more frequently associated with drugs like **aminoglycosides** or high-dose **loop diuretics**.
Want unlimited practice?
Get full access to all questions, explanations, and performance tracking.
Start For Free