Antimicrobial Agents Practice Questions

Q: Dapsone is used for treatment of bacterial infections as well as for immunomodulatory actions. What is mechanism of dapsone for these indications?

Competition with PABA in folic acid synthesis. ***Competition with PABA in folic acid synthesis*** - **Dapsone** is a **sulfone drug** that functions as a competitive antagonist of **para-aminobenzoic acid (PABA)**. - This competition blocks the enzyme **dihydropteroate synthase**, preventing **folic acid synthesis** in susceptible bacteria, which is essential for their growth. *Inhibition of cell wall synthesis* - This mechanism is characteristic of **beta-lactam antibiotics** (penicillins, cephalosporins) and **glycopeptides** (vancomycin), which target peptidoglycan synthesis. - **Dapsone** does not interfere with cell wall integrity or synthesis. *Inhibition of ergosterol in cell membranes* - This is the primary mechanism of action for many **antifungal drugs**, such as **azoles** (fluconazole) and **polyenes** (amphotericin B). - **Dapsone** does not target fungal cell membranes or ergosterol synthesis. *Inhibition of protein synthesis* - This mechanism is employed by various classes of **antibiotics**, including **tetracyclines**, **macrolides**, and **aminoglycosides**, which bind to bacterial ribosomes. - **Dapsone's** mechanism is distinct from inhibiting protein production.

Q: A patient on anti-tubercular therapy develops tingling sensation in the limbs. Which of the following when supplemented can result in improvement of symptoms?

Pyridoxine. ***Pyridoxine*** - **Isoniazid**, a key anti-tubercular drug, can cause **peripheral neuropathy** due to its interference with **pyridoxine (vitamin B6)** metabolism. - Supplementation with **pyridoxine** is crucial to prevent and treat this neurological side effect, leading to an improvement in tingling sensations. *Folic acid* - **Folic acid** (vitamin B9) deficiency can cause **megaloblastic anemia** and some neurological symptoms, but it is not directly related to isoniazid-induced peripheral neuropathy. - While beneficial for overall health, it would not specifically address the tingling caused by anti-tubercular therapy. *Thiamine* - **Thiamine (vitamin B1)** deficiency can cause **beriberi**, leading to peripheral neuropathy, but it is not the primary vitamin implicated in isoniazid-induced neuropathy. - Substituting thiamine would not effectively reverse the specific mechanism of nerve damage caused by isoniazid. *Methylcobalamine* - **Methylcobalamine** (Mecobalamin) is a form of **vitamin B12** and is used to treat **vitamin B12 deficiency**, which can also cause neuropathy. - However, the neuropathy associated with anti-tubercular therapy, specifically isoniazid, is primarily linked to **pyridoxine deficiency**, not B12 deficiency.

Q: Which of the following anti-leprosy drugs can cause skin hyperpigmentation?

Clofazimine. ***Clofazimine*** - **Clofazimine** is known to cause dose-dependent **hyperpigmentation** of the skin, ranging from reddish-brown to dark brown, and can also discolor bodily fluids. - This side effect is due to the drug's accumulation in macrophages and subsequent deposition in the dermis and subcutaneous fat. *Rifampicin* - **Rifampicin** can cause harmless **reddish-orange discoloration** of urine, sweat, tears, and other bodily secretions. - It is not typically associated with **skin hyperpigmentation** (darkening of the skin itself). *Ofloxacin* - **Ofloxacin** is a fluoroquinolone antibiotic primarily used in leprosy treatment as a second-line agent. - Its common side effects include gastrointestinal disturbances and nervous system effects, but **skin hyperpigmentation** is not a characteristic adverse event. *Dapsone* - **Dapsone** is a sulfone drug and a cornerstone of leprosy treatment, but it is not associated with **skin hyperpigmentation**. - Its most notable side effects include **hemolysis**, especially in patients with **G6PD deficiency**, and methemoglobinemia.

Q: A 45-year-old patient with a known allergy to penicillin presents with an enterococcal endocarditis. The physician needs to prescribe an antibiotic but wants to ensure it is safe for a penicillin allergy. The patient has had previous allergic reactions to penicillin including rash & swelling. Which of the following drugs can be used safely in a patient allergic to penicillin?

Vancomycin. ***Vancomycin*** - **Vancomycin** is a glycopeptide antibiotic with a completely different mechanism of action and chemical structure compared to penicillins, making it **safe for patients with penicillin allergy**. - It is the **first-line treatment for enterococcal endocarditis** in patients with penicillin allergy, providing excellent coverage against both *Enterococcus faecalis* and *E. faecium*. - No cross-reactivity with beta-lactam antibiotics. *Ceftriaxone* - **Ceftriaxone** is a third-generation **cephalosporin**, a beta-lactam antibiotic with structural similarity to penicillin. - There is **5-10% cross-reactivity risk** in patients with IgE-mediated penicillin allergy (rash, swelling, anaphylaxis), making it potentially unsafe in this patient. - Should be avoided in patients with a history of immediate hypersensitivity reactions to penicillin. *Piperacillin* - **Piperacillin** is a **penicillin derivative** (ureidopenicillin) and shares the same beta-lactam core structure that triggers allergic reactions. - **Absolutely contraindicated** in patients with known penicillin allergy—would almost certainly provoke an allergic reaction. - Using this drug would expose the patient to significant risk of anaphylaxis. *Aztreonam* - **Aztreonam** is a **monobactam** with minimal cross-reactivity (<1%) with penicillins and is generally **safe for penicillin-allergic patients** from an allergy perspective. - However, aztreonam has **primarily gram-negative coverage** and **poor activity against enterococci**, making it ineffective for treating enterococcal endocarditis. - While safe regarding allergy concerns, it is not the appropriate choice due to **lack of efficacy** against the causative organism.

Q: Drug of choice for Enterococcus infection in a patient allergic to penicillin?

Vancomycin. ***Vancomycin*** - **Vancomycin** is a glycopeptide antibiotic that is effective against **Gram-positive bacteria**, including *Enterococcus*, especially in patients with a **penicillin allergy**. - It inhibits **cell wall synthesis** by binding to the D-Ala-D-Ala terminus of peptidoglycan precursors, a different mechanism from penicillins. *Streptomycin* - **Streptomycin** is an aminoglycoside that inhibits **protein synthesis** and is primarily used in **combination therapy** for serious *Enterococcal* infections, but typically alongside a cell-wall active agent (like penicillin or vancomycin) for synergistic killing in endocarditis or other severe infections. - It is not usually recommended as a **monotherapy** for *Enterococcus*, especially in the context of penicillin allergy, as it doesn't provide bactericidal activity on its own against all enterococcal strains. *Cephalosporin* - **Cephalosporins** are **not active** against *Enterococcus spp.* as these bacteria intrinsically lack the **penicillin-binding proteins (PBPs)** that cephalosporins target effectively. - This **intrinsic resistance** makes cephalosporins an inappropriate choice for treating *Enterococcal* infections, regardless of penicillin allergy status. *Rifampicin* - **Rifampicin** is an antibiotic primarily used for **Mycobacterial infections** (e.g., tuberculosis) and some **Staphylococcal infections**, often in combination to prevent resistance. - It has **poor activity** against *Enterococcus* and is not a recommended treatment for *Enterococcal* infections.

Q: Which drug is most likely to induce photosensitivity?

Tetracycline. ***Tetracycline*** - **Tetracyclines** are well-known to cause **photosensitivity reactions**, leading to exaggerated sunburns, rashes, or skin discoloration upon sun exposure. - This adverse effect is thought to be due to an interaction between the drug and UV light, leading to the formation of reactive oxygen species and subsequent cell damage. *Metronidazole* - While metronidazole can cause a variety of side effects, significant **photosensitivity** is generally not considered a common or prominent adverse reaction. - It is often associated with a **disulfiram-like reaction** when consumed with alcohol, as well as gastrointestinal upset and a metallic taste. *Ivermectin* - **Ivermectin** is primarily used as an antiparasitic agent and is not typically associated with **photosensitivity** as a common side effect. - Its main adverse effects are usually related to the Mazzotti reaction during treatment of onchocerciasis or other systemic symptoms like dizziness or nausea. *Fluconazole* - **Fluconazole**, an antifungal medication, has a relatively low incidence of causing **photosensitivity** compared to other drug classes. - Common side effects include gastrointestinal disturbances, headache, and elevated liver enzymes, but severe phototoxic reactions are rare.

Q: Which of the following is NOT a mechanism of antibiotic resistance?

Increased drug absorption. ***Increased drug absorption*** - **Increased drug absorption** would lead to a higher intracellular concentration of the antibiotic, making it *more potent* against the bacteria rather than contributing to resistance. - Antibiotic resistance mechanisms aim to *reduce the effective concentration* of the drug at its target site or *alter the target itself*. *Efflux pump activity* - **Efflux pumps** are bacterial membrane proteins that actively pump antibiotics out of the bacterial cell [3]. - This mechanism *reduces the intracellular concentration* of the antibiotic, preventing it from reaching its therapeutic target [3]. *Inactivation by enzymes such as beta-lactamase* - Bacteria can produce enzymes like **beta-lactamase** that *chemically modify or degrade* the antibiotic molecule, rendering it inactive [2]. - This is a common mechanism of resistance against **beta-lactam antibiotics** (e.g., penicillin, cephalosporins) [2]. *Modification of drug target sites* - Bacteria can develop mutations that *alter the structure of the antibiotic's target site*, such as a bacterial ribosome or cell wall component [1]. - This change in the target means the antibiotic can no longer bind effectively or interfere with cellular processes, thus *losing its efficacy* [1].

Q: Which antimicrobial inhibits cell wall synthesis?

Vancomycin. ***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.

Q: Which antiretroviral drug causes hyperpigmentation?

Emtricitabine. ***Emtricitabine*** - **Emtricitabine** is a nucleoside reverse transcriptase inhibitor (NRTI) most commonly known to cause mucocutaneous hyperpigmentation, particularly on the **palms and soles**. - This side effect is more commonly seen in individuals with darker skin tones and can manifest as **darkening of nails** or skin. - Among NRTIs, emtricitabine has the **highest incidence** of hyperpigmentation. *Nevirapine* - **Nevirapine** is a non-nucleoside reverse transcriptase inhibitor (NNRTI) primarily associated with **rash**, including severe cases like Stevens-Johnson syndrome. - It does not typically cause **hyperpigmentation** as a prominent side effect. *Efavirenz* - **Efavirenz** is another NNRTI commonly associated with **central nervous system side effects** such as dizziness, vivid dreams, and psychiatric symptoms. - While skin rash can occur, **hyperpigmentation** is not a characteristic adverse effect of efavirenz. *Zidovudine* - **Zidovudine** (AZT) is an NRTI known for causing **bone marrow suppression** (anemia, neutropenia) and **myopathy**. - While zidovudine can cause **nail and skin hyperpigmentation**, this side effect occurs **less frequently** compared to emtricitabine, making emtricitabine the more characteristic answer for hyperpigmentation among antiretroviral drugs.

Q: Which TB drug causes optic neuritis as a side effect?

Ethambutol. ***Ethambutol*** - **Ethambutol** is known to cause **optic neuritis**, leading to **decreased visual acuity** and impaired **red-green color discrimination**. - This side effect is **dose-dependent** and usually **reversible** upon discontinuing the drug, though permanent damage can occur with prolonged use. *Isoniazid* - **Isoniazid** is primarily associated with **peripheral neuropathy** and **hepatotoxicity**, which can be mitigated with **pyridoxine (vitamin B6)** supplementation. - While visual disturbances can occur, **optic neuritis** is not its most characteristic or frequent ocular side effect. *Pyrazinamide* - The main side effects of **pyrazinamide** include **hepatotoxicity** and **hyperuricemia**, which can lead to **gouty arthritis**. - It does not typically cause **optic neuritis** or other significant ocular complications. *Rifampicin* - **Rifampicin** is well-known for causing **hepatotoxicity**, **red-orange discoloration of body fluids** (urine, tears, sweat), and various **drug interactions** due to enzyme induction. - Ocular side effects like **optic neuritis** are not a common or characteristic adverse effect of rifampicin.

Question 1

Dapsone is used for treatment of bacterial infections as well as for immunomodulatory actions. What is mechanism of dapsone for these indications?

Accepted Answer

Competition with PABA in folic acid synthesis

Answer

Inhibition of cell wall synthesis

Answer

Inhibition of ergosterol in cell membranes

Answer

Inhibition of protein synthesis

Question 2

A patient on anti-tubercular therapy develops tingling sensation in the limbs. Which of the following when supplemented can result in improvement of symptoms?

Accepted Answer

Pyridoxine

Answer

Folic acid

Answer

Thiamine

Answer

Methylcobalamine

Question 3

Which of the following anti-leprosy drugs can cause skin hyperpigmentation?

Accepted Answer

Clofazimine

Answer

Rifampicin

Answer

Ofloxacin

Answer

Dapsone

Question 4

A 45-year-old patient with a known allergy to penicillin presents with an enterococcal endocarditis. The physician needs to prescribe an antibiotic but wants to ensure it is safe for a penicillin allergy. The patient has had previous allergic reactions to penicillin including rash & swelling. Which of the following drugs can be used safely in a patient allergic to penicillin?

Accepted Answer

Vancomycin

Answer

Ceftriaxone

Answer

Piperacillin

Answer

Aztreonam

Question 5

Drug of choice for Enterococcus infection in a patient allergic to penicillin?

Accepted Answer

Vancomycin

Answer

Streptomycin

Answer

Cephalosporin

Answer

Rifampicin

Question 6

Which drug is most likely to induce photosensitivity?

Accepted Answer

Tetracycline

Answer

Metronidazole

Answer

Ivermectin

Answer

Fluconazole

Question 7

Which of the following is NOT a mechanism of antibiotic resistance?

Accepted Answer

Increased drug absorption

Answer

Efflux pump activity

Answer

Inactivation by enzymes such as beta-lactamase

Answer

Modification of drug target sites

Question 8

Which antimicrobial inhibits cell wall synthesis?

Accepted Answer

Vancomycin

Answer

Metronidazole

Answer

Azithromycin

Answer

Ciprofloxacin

Question 9

Which antiretroviral drug causes hyperpigmentation?

Accepted Answer

Emtricitabine

Answer

Nevirapine

Answer

Efavirenz

Answer

Zidovudine

Question 10

Which TB drug causes optic neuritis as a side effect?

Accepted Answer

Ethambutol

Answer

Isoniazid

Answer

Pyrazinamide

Answer

Rifampicin

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

On this page

Practice by Chapter

Want unlimited practice?