Antimicrobial Agents Practice Questions

Q: A patient on anti-tubercular drug therapy developed tingling sensation in the lower limbs. Which of the following drugs should be used for the treatment?

Pyridoxine. ***Pyridoxine*** - **Isoniazid**, a common anti-tubercular drug, can cause peripheral neuropathy due to its interference with **pyridoxine (vitamin B6)** metabolism [1]. Supplementation with **pyridoxine** is essential to prevent and treat this neuropathy, which manifests as a tingling sensation in the limbs [1]. *Thiamine* - **Thiamine (vitamin B1)** deficiency is associated with conditions like **beriberi** and **Wernicke-Korsakoff syndrome**, presenting with neurological and cardiac symptoms. It is not directly implicated in peripheral neuropathy caused by anti-tubercular drugs. *Folic acid* - **Folic acid** is important for DNA synthesis and red blood cell formation; deficiency can lead to **megaloblastic anemia** and some neurological symptoms. It does not directly address the mechanism of anti-tubercular drug-induced peripheral neuropathy. *Vitamin B-12* - **Vitamin B12 (cobalamin)** deficiency causes **pernicious anemia** and neurological symptoms like subacute combined degeneration of the spinal cord. While essential for nerve health, it is not the primary vitamin involved in preventing or reversing isoniazid-induced neuropathy.

Q: Which of the following is a clinical use of tafenoquine?

Radical cure of Plasmodium vivax. ***Radical cure of Plasmodium vivax*** - **Tafenoquine** is an 8-aminoquinoline derivative used for the **radical cure of *Plasmodium vivax*** malaria, targeting the **hypnozoites** in the liver. - It is effective in preventing relapse by clearing the dormant liver stages of the parasite. *Treatment of severe falciparum malaria* - **Severe falciparum malaria** is typically treated with intravenous **artesunate**, not tafenoquine. - Tafenoquine is not indicated for the acute treatment of severe, life-threatening malaria. *Prophylaxis of malaria in pregnancy* - **Tafenoquine** is **contraindicated in pregnancy** due to potential risks to the fetus and the mother, especially in case of **G6PD deficiency**. - **Mefloquine** and **chloroquine** are generally preferred for malaria prophylaxis in pregnant women, depending on local resistance patterns. *Treatment of endemic malaria in children < 2 years* - **Tafenoquine** is not approved for use in **children under 2 years of age** due to insufficient safety and efficacy data. - The risk of **hemolytic anemia** in children with undiagnosed G6PD deficiency adds to this contraindication.

Q: Which of the following drugs has gametocidal action against all species of Plasmodium?

Primaquine. ***Primaquine*** - **Primaquine** is a **8-aminoquinoline** that is effective against the **gametocytes** of all *Plasmodium* species, including *P. falciparum*. - Its gametocidal action is crucial for **blocking transmission** of malaria, as gametocytes are the parasite forms ingested by mosquitoes. *Quinine* - **Quinine** is a **blood schizonticide** primarily used for treating acute, uncomplicated malaria, especially due to **chloroquine-resistant *P. falciparum***. - While it has some activity against *P. vivax* and *P. malariae* gametocytes, its action against mature *P. falciparum* gametocytes is limited. *Chloroquine* - **Chloroquine** is a highly effective **blood schizonticide** for **sensitive *P. falciparum***, *P. vivax*, *P. ovale*, and *P. malariae*. - It rapidly clears asexual parasites but has no effect on **mature *P. falciparum* gametocytes** and therefore does not prevent transmission of this species. *None of the options* - This option is incorrect because **Primaquine** possesses the described broad-spectrum gametocidal activity.

Q: All of the following drugs require dose reduction in renal failure except?

Doxycycline. ***Doxycycline*** - **Doxycycline** is primarily eliminated via the gastrointestinal tract (fecal excretion) and does NOT require dose adjustment in patients with **renal impairment**. [1] - Its unique elimination pathway makes it a safe choice for treating infections in patients with **renal failure**. - This is a key distinguishing feature among tetracyclines. *Vancomycin* - **Vancomycin** is predominantly eliminated by the kidneys (80-90% unchanged in urine). - Accumulation in renal failure can lead to **ototoxicity** and **nephrotoxicity**. - Dosage must be carefully adjusted based on **creatinine clearance** and therapeutic drug monitoring is essential. *Gentamicin* - **Gentamicin**, an aminoglycoside, is almost entirely excreted unchanged by the kidneys. - Highly **nephrotoxic** and **ototoxic** with narrow therapeutic index. - Dose reduction and extended dosing intervals are critical in **renal failure** to prevent drug accumulation and serious adverse effects. [3] *Acyclovir* - **Acyclovir** is primarily eliminated renally (60-90% excreted unchanged in urine). - Requires significant **dose reduction in renal impairment** to prevent crystalluria and neurotoxicity. [2] - Dosing adjustment based on creatinine clearance is mandatory to avoid adverse effects.

Q: A patient with TB on DOTS develops orange-red discoloration of urine and tears. Which drug is responsible?

Rifampicin. ***Rifampicin*** - **Rifampicin** is well-known for causing **orange-red discoloration** of urine, sweat, tears, and other body fluids due to its intrinsic color. - This side effect is benign and does not indicate liver damage or other serious toxicity, but patients should be informed about it. *Ethambutol* - **Ethambutol** is primarily associated with **optic neuritis**, leading to decreased visual acuity and red-green color blindness. - It does not cause discoloration of body fluids. *Pyrazinamide* - **Pyrazinamide** is commonly associated with **hepatotoxicity** and **hyperuricemia**, which can lead to gout. - It does not cause discoloration of body fluids. *Isoniazid* - **Isoniazid** is known to cause **peripheral neuropathy** (prevented by pyridoxine supplementation) and **hepatotoxicity**. - It does not cause discoloration of body fluids.

Q: Which antifungal binds to ergosterol, causing fungal cell membrane damage?

Amphotericin B. Amphotericin B - **Amphotericin B** is a polyene antifungal that directly binds to **ergosterol**, the primary sterol in fungal cell membranes [2]. - This binding creates pores in the membrane, leading to leakage of intracellular components and ultimately **fungal cell death** [2]. Caspofungin - **Caspofungin** is an echinocandin, which inhibits the synthesis of **β-(1,3)-D-glucan**, a vital component of the fungal cell wall. - Its mechanism of action is distinct from ergosterol binding and primarily targets cell wall integrity rather than the cell membrane directly. Terbinafine - **Terbinafine** is an allylamine antifungal that inhibits **squalene epoxidase**, an enzyme involved in ergosterol synthesis. - By blocking this enzyme, it prevents the formation of ergosterol, leading to an accumulation of toxic squalene and disrupting membrane function, but it does not directly bind to ergosterol. Fluconazole - **Fluconazole** is an azole antifungal that inhibits **lanosterol 14-α-demethylase**, a cytochrome P450 enzyme responsible for an earlier step in ergosterol synthesis [1]. - This action prevents ergosterol production, impairing membrane function, but it does not involve direct binding to pre-existing ergosterol [1].

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.

Question 1

A patient on anti-tubercular drug therapy developed tingling sensation in the lower limbs. Which of the following drugs should be used for the treatment?

Accepted Answer

Pyridoxine

Answer

Thiamine

Answer

Folic acid

Answer

Vitamin B-12

Question 2

Which of the following is a clinical use of tafenoquine?

Accepted Answer

Radical cure of Plasmodium vivax

Answer

Treatment of severe falciparum malaria

Answer

Prophylaxis of malaria in pregnancy

Answer

Treatment of endemic malaria in children < 2 years

Question 3

Which of the following drugs has gametocidal action against all species of Plasmodium?

Accepted Answer

Primaquine

Answer

Quinine

Answer

Chloroquine

Answer

None of the options

Question 4

All of the following drugs require dose reduction in renal failure except?

Accepted Answer

Doxycycline

Answer

Vancomycin

Answer

Gentamicin

Answer

Acyclovir

Question 5

A patient with TB on DOTS develops orange-red discoloration of urine and tears. Which drug is responsible?

Accepted Answer

Rifampicin

Answer

Ethambutol

Answer

Pyrazinamide

Answer

Isoniazid

Question 6

Which antifungal binds to ergosterol, causing fungal cell membrane damage?

Accepted Answer

Amphotericin B

Answer

Caspofungin

Answer

Terbinafine

Answer

Fluconazole

Question 7

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 8

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 9

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

Accepted Answer

Clofazimine

Answer

Rifampicin

Answer

Ofloxacin

Answer

Dapsone

Question 10

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

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

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