Antimicrobial Agents Practice Questions

Q: Agents most effective and best tolerated in the management of onychomycosis?

Itraconazole and terbinafine. ***Itraconazole and terbinafine*** - **Terbinafine** is a highly effective **allylamine antifungal** for onychomycosis, achieving high cure rates with good tolerability due to its fungicidal action and accumulation in the nail plate. - **Itraconazole** is a **triazole antifungal** that is also effective for onychomycosis, particularly for both dermatophyte and non-dermatophyte infections, and can be given in pulse doses which may improve patient compliance and reduce side effects. *Ciclopirox and griseofulvin* - **Ciclopirox** is a topical agent, generally less effective for moderate to severe onychomycosis, and requires prolonged daily application. - **Griseofulvin** has a lower cure rate for onychomycosis compared to newer antifungals like terbinafine and itraconazole, and requires longer treatment durations with potential for more drug interactions. *Griseofulvin and ketoconazole* - **Griseofulvin** has been largely supplanted by newer antifungals due to its lower efficacy and longer treatment courses for onychomycosis. - **Ketoconazole** has a less favorable safety profile (e.g., hepatotoxicity) for systemic use in onychomycosis and is generally not recommended as a first-line treatment. *Griseofulvin and caspofungin* - **Griseofulvin** is an older oral antifungal with limited efficacy and prolonged treatment duration for onychomycosis. - **Caspofungin** is an **echinocandin** antifungal primarily used for systemic candidiasis and aspergillosis, and is not indicated for the treatment of onychomycosis.

Q: Cilastatin is given in combination with Imipenem because:-

Cilastatin prevents degradation of Imipenem in kidney. ***Cilastatin prevents degradation of Imipenem in kidney*** - **Imipenem** is extensively metabolized in the renal tubules by the enzyme **dihydropeptidase-I**, leading to its inactivation and potential nephrotoxicity. - **Cilastatin** is a **dihydropeptidase-I inhibitor** that prevents this enzymatic breakdown, increasing the bioavailability and efficacy of imipenem and reducing the risk of renal damage. *Inhibits the enzymes that digest Imipenem in stomach* - **Imipenem** is a parenteral antibiotic and is not administered orally; therefore, degradation in the stomach is not a relevant concern. - Its combination with cilastatin is specifically to address renal metabolism, not gastric degradation. *Cilastatin increase absorption of Imipenem* - **Cilastatin** does not enhance the absorption of imipenem; its role is primarily to inhibit renal metabolism. - Imipenem is administered intravenously, bypassing the need for gastrointestinal absorption. *Reduces side effects of Imipenem* - While cilastatin does prevent the formation of nephrotoxic metabolites of imipenem, its primary role is to **maintain therapeutic levels** and prevent drug inactivation. - The reduction in **nephrotoxicity** is a consequence of preventing degradation, rather than a direct mitigation of general side effects.

Q: In the treatment of granuloma inguinale, which antibiotic regimen is most appropriate?

Doxycycline 100mg BD until lesions heal. ***Doxycycline 100mg BD until lesions heal*** - **Doxycycline** is the recommended first-line treatment for **granuloma inguinale** (donovanosis) due to its effectiveness against **Klebsiella granulomatis**, the causative agent. - Treatment should continue until all lesions have completely healed, which may take at least 3 weeks or longer, to prevent relapse. *Ceftriaxone 250mg IM single dose* - This regimen is typically used for the treatment of **gonorrhea**, not granuloma inguinale. - While effective for some bacterial infections, it is not the appropriate therapy for **Klebsiella granulomatis**. *Azithromycin single dose 1g* - A single 1g dose of **azithromycin** is the standard treatment for **Chlamydia trachomatis** infections. - While azithromycin IS an alternative treatment for granuloma inguinale, it requires **1g weekly or 500mg daily** for at least 3 weeks, not a single dose. - The single-dose regimen shown here is therefore inappropriate for granuloma inguinale. *Penicillin G 2.4 million units IM* - This dosage of **penicillin G** is specifically used to treat **syphilis**, particularly early-stage syphilis. - It has no role in the treatment of granuloma inguinale.

Q: Drug of choice for scrub typhus is:

Doxycycline. ***Doxycycline*** - **Doxycycline** is the drug of choice for **scrub typhus** in both adults and children due to its high efficacy. - It is a **tetracycline antibiotic** that inhibits bacterial protein synthesis, providing broad-spectrum coverage against *Orientia tsutsugamushi*. *Ciprofloxacin* - **Ciprofloxacin** is a **fluoroquinolone antibiotic** primarily used for bacterial infections, but it is **not effective** against *Orientia tsutsugamushi*. - It is generally reserved for specific conditions like urinary tract infections or some severe bacterial infections where other antibiotics are ineffective. *Azithromycin* - **Azithromycin** is a **macrolide antibiotic** that can be used as an alternative therapy for **scrub typhus**, especially in **pregnant women** and young children where doxycycline is contraindicated. - While effective, it is considered a **second-line agent** after doxycycline due to potentially slower resolution of symptoms. *Chloramphenicol* - **Chloramphenicol** was historically used for scrub typhus and is still effective, but its use is limited due to potential **severe side effects** like **bone marrow suppression** and **aplastic anemia**. - Due to these significant toxicities, it is generally reserved for cases where other safer and equally effective antibiotics are contraindicated or ineffective.

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].

Question 1

Agents most effective and best tolerated in the management of onychomycosis?

Accepted Answer

Itraconazole and terbinafine

Answer

Ciclopirox and griseofulvin

Answer

Griseofulvin and ketoconazole

Answer

Griseofulvin and caspofungin

Question 2

Cilastatin is given in combination with Imipenem because:-

Accepted Answer

Cilastatin prevents degradation of Imipenem in kidney

Answer

Inhibits the enzymes that digest Imipenem in stomach

Answer

Reduces side effects of Imipenem

Answer

Cilastatin increases absorption of Imipenem

Question 3

In the treatment of granuloma inguinale, which antibiotic regimen is most appropriate?

Accepted Answer

Doxycycline 100mg BD until lesions heal

Answer

Ceftriaxone 250mg IM single dose

Answer

Azithromycin single dose 1g

Answer

Penicillin G 2.4 million units IM

Question 4

Drug of choice for scrub typhus is:

Accepted Answer

Doxycycline

Answer

Ciprofloxacin

Answer

Azithromycin

Answer

Chloramphenicol

Question 5

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 6

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 7

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 8

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

Accepted Answer

Doxycycline

Answer

Vancomycin

Answer

Gentamicin

Answer

Acyclovir

Question 9

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 10

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

Accepted Answer

Amphotericin B

Answer

Caspofungin

Answer

Terbinafine

Answer

Fluconazole

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

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