Antimicrobial Agents Practice Questions

Q: Which of the following statements about the primary clinical use of levamisole is true?

It is used against ascariasis and ancyclostomiasis. ***It is used against ascariasis and ancyclostomiasis*** - **Levamisole** is an **anthelmintic drug** primarily used for the treatment of **nematode infections**, specifically **roundworms (Ascaris lumbricoides)** and **hookworms (Ancylostoma duodenale)**. - It works by **paralyzing the worms**, leading to their expulsion in the feces. *It is the levoisomer of tetramisole* - While it is true that **levamisole** is the **levorotatory isomer** of **tetramisole**, this statement describes its chemical structure, not its primary clinical use. - **Tetramisole** itself exists as a **racemic mixture** of both levo and dextro isomers. *It has immunomodulator action* - **Levamisole** does possess **immunomodulatory properties** at lower doses and was historically investigated for conditions like **rheumatoid arthritis** and as an adjuvant in colon cancer. - However, its primary and most widespread clinical use is as an **anthelmintic**, not as an immunomodulator, especially due to concerns about side effects like **agranulocytosis**. *It can kill strongyloides larvae and adult worms* - **Levamisole** is **not effective** against **Strongyloides stercoralis** (threadworms). - The drug of choice for **strongyloidiasis** is typically **ivermectin** or **albendazole**.

Q: Which compound is primarily responsible for the hepatotoxicity associated with Isoniazid (INH)?

INH acetylhydrazine. ***INH acetylhydrazine*** - The hepatotoxicity of Isoniazid (INH) is primarily attributed to **acetylhydrazine**, a toxic metabolite formed during INH metabolism - **Metabolic pathway:** INH is first acetylated by N-acetyltransferase 2 (NAT2) to form acetylisoniazid, which then hydrolyzes to **acetylhydrazine** and isonicotinic acid - Acetylhydrazine is further oxidized by **cytochrome P450 2E1 (CYP2E1)** to form highly reactive intermediates that covalently bind to hepatic macromolecules, causing **hepatocellular injury** - **Risk factors:** Rapid acetylators, concurrent alcohol use, and CYP2E1 inducers increase acetylhydrazine formation and hepatotoxicity risk - This is the well-established mechanism of INH-induced hepatitis in clinical pharmacology *INH sulfhydrazine* - Sulfhydrazine is not a metabolite of isoniazid - INH metabolism involves acetylation and hydrolysis, not sulfonation pathways - This compound is not implicated in INH hepatotoxicity *INH methylhydrazine* - Methylhydrazine is not formed during isoniazid metabolism - The metabolic pathway of INH involves acetylation, not methylation - While hydrazine compounds can be hepatotoxic, methylhydrazine is not relevant to INH toxicity *None of the options* - This is incorrect as acetylhydrazine (listed as "INH acetylhydrazine") is indeed the primary toxic metabolite responsible for hepatotoxicity

Q: Typhoid is treated by all except

Erythromycin. ***Erythromycin*** - **Erythromycin** is a macrolide antibiotic primarily effective against Gram-positive bacteria and atypical bacteria. - It has **NO role** in the treatment of typhoid fever as it lacks adequate activity against *Salmonella typhi* and does not achieve therapeutic intracellular concentrations. - Unlike azithromycin (another macrolide), erythromycin has poor intracellular penetration and is **never used** for typhoid. *Ceftriaxone* - **Ceftriaxone** is a third-generation cephalosporin that is highly effective against *Salmonella typhi*. - It is a **first-line treatment** for severe typhoid fever and is preferred in regions with fluoroquinolone resistance. - Dosage: 2-4 g IV daily for 10-14 days. *Amikacin* - **Amikacin** is an aminoglycoside with generally poor intracellular penetration, making it suboptimal for treating intracellular pathogens. - While **not a standard agent** for typhoid, it has been used in **rare cases of extensively drug-resistant (XDR) typhoid** as part of combination therapy, particularly in outbreaks where other options have failed. - It is **not a recommended first-line or routine agent** due to limited efficacy, potential toxicity (nephrotoxicity and ototoxicity), and availability of better alternatives. *Ciprofloxacin* - **Ciprofloxacin** is a fluoroquinolone with excellent intracellular penetration and was historically the **first-line oral treatment** for uncomplicated typhoid fever. - Its efficacy against *Salmonella typhi* made it the preferred agent for decades. - However, widespread **fluoroquinolone resistance** has emerged in South Asia, limiting its current use as empirical first-line therapy in many regions.

Q: Anti-HIV drug used for prevention of vertical transmission?

Nevirapine. ***Nevirapine*** - **Nevirapine** is a non-nucleoside reverse transcriptase inhibitor (NNRTI) that was historically used in resource-limited settings for the prevention of **mother-to-child transmission (MTCT)** of HIV. - A single dose of **nevirapine** given to the mother during labor and to the neonate within 72 hours of birth was shown to significantly reduce the risk of **vertical transmission** (HIVNET 012 trial) [1]. - **Historical significance**: This was a landmark approach in the early 2000s when resources were limited. - **Current practice note**: Modern guidelines (WHO, 2023+) now recommend **combination antiretroviral therapy (cART)** for all pregnant women with HIV, rather than single-dose nevirapine, due to superior efficacy and reduced resistance risk [1]. *Lamivudine* - **Lamivudine** is a nucleoside reverse transcriptase inhibitor (NRTI) that is **part of current combination therapy regimens** for prevention of mother-to-child transmission. - It is not used alone but is a component of **cART regimens** recommended in modern PMTCT protocols. - In the historical context of this question, it was not the single-agent answer being sought. *Efavirenz* - **Efavirenz** is an NNRTI now used in HIV treatment regimens for pregnant women in current PMTCT protocols. - Previous concerns about first-trimester teratogenicity have been re-evaluated, and it is included in WHO-recommended regimens [1]. - However, in the context of single-drug prophylaxis (historical approach), nevirapine was preferred. *Tenofovir* - **Tenofovir** is a nucleotide reverse transcriptase inhibitor (NtRTI) and is the **backbone of current first-line cART regimens** for pregnant women with HIV. - It is highly effective as part of combination therapy for PMTCT. - It was not used as a single-dose prophylactic agent in the historical context of this question.

Q: Which of the following can prolong QT interval?

Gatifloxacin. ***Gatifloxacin*** - This **fluoroquinolone antibiotic** is known to cause **significant QT prolongation**, which can lead to serious cardiac arrhythmias like **Torsades de Pointes** [1]. - Among fluoroquinolones, gatifloxacin carries the **highest risk** of QT interval prolongation. - Its use has been **withdrawn or restricted** in many countries due to these **serious cardiac side effects** and dysglycemia, especially in patients with pre-existing cardiac conditions. - This is the **best answer** as it has the most clinically significant association with QT prolongation. *Nalidixic acid* - This is a **first-generation quinolone** primarily used for **urinary tract infections**. - While it can theoretically prolong QT interval, the **clinical significance is much lower** compared to fluoroquinolones. - It is **rarely implicated** in clinically significant QT prolongation in practice. *Ofloxacin* - Ofloxacin is a **second-generation fluoroquinolone** with a **moderate risk** of QT prolongation. - All fluoroquinolones carry a **class warning** for QT effects, but ofloxacin has **significantly lower risk** compared to gatifloxacin, moxifloxacin, and sparfloxacin. - It is considered **relatively safer** within the fluoroquinolone class for cardiac effects. *Pefloxacin* - Pefloxacin is another **second-generation fluoroquinolone** with **moderate QT prolongation potential**. - Like ofloxacin, it has a **comparatively lower risk** than gatifloxacin. - The **clinical incidence** of significant QT prolongation is **much less** than with newer fluoroquinolones.

Q: Which antibiotic is known to cause irreversible hearing loss?

Gentamicin. ***Gentamicin*** - **Gentamicin** is an **aminoglycoside antibiotic** well-known for its potential to cause **irreversible ototoxicity**, which manifests as permanent hearing loss due to damage to the **cochlear hair cells**. - The risk of ototoxicity is increased with higher doses, prolonged treatment, underlying renal impairment, and concomitant use of other ototoxic drugs. - Aminoglycosides cause concentration-dependent killing and have a narrow therapeutic window, requiring therapeutic drug monitoring. *Clarithromycin* - **Clarithromycin** is a **macrolide antibiotic** that can cause **reversible ototoxicity**, typically manifesting as temporary hearing loss or tinnitus. - Unlike aminoglycosides, the hearing impairment associated with clarithromycin usually resolves upon discontinuation of the drug. - This occurs more commonly with high doses or in patients with renal/hepatic impairment. *Vancomycin* - **Vancomycin** is a **glycopeptide antibiotic** that can cause ototoxicity, particularly when used at high doses or in combination with other ototoxic agents like aminoglycosides. - However, vancomycin-related ototoxicity is **less common and less severe** compared to aminoglycosides, and cases of permanent hearing loss are rare with modern dosing regimens. - The ototoxicity risk is primarily associated with older high-dose formulations. *None of the options* - This option is incorrect because **Gentamicin** is definitively known to cause irreversible hearing loss. - Aminoglycoside ototoxicity is a well-established and clinically significant adverse drug reaction that requires careful monitoring during therapy.

Q: Colistin is obtained from ?

Bacteria. ***Bacteria*** - Colistin, also known as **polymyxin E**, is an antibiotic derived from the bacterium **Bacillus polymyxa subspecies colistinus** (now reclassified as *Paenibacillus polymyxa*). - It works by disrupting the **outer membrane** of Gram-negative bacteria, making it effective against multi-drug resistant strains. - While actinomycetes are also bacteria, in pharmacology, antibiotics from **Bacillus species** are categorized separately from actinomycete-derived drugs. *Fungi* - Many common antibiotics, such as **penicillin** and **cephalosporins**, are derived from fungi (e.g., *Penicillium*, *Cephalosporium*), but colistin is not one of them. - Fungal-derived antibiotics typically target bacterial **cell wall synthesis** or **protein synthesis**. *Actinomycetes* - **Actinomycetes**, particularly from the *Streptomyces* genus, are a rich source of antibiotics, including **streptomycin**, **tetracyclines**, and **erythromycin**. - While actinomycetes are technically bacteria, they are classified separately in pharmacology due to their unique characteristics and prolific antibiotic production. - Colistin is specifically produced by **Bacillus species**, not actinomycetes. *Herbs* - Herbs are used for traditional medicine and can have various therapeutic properties, but they do **not produce antibiotics** like colistin. - While some plant-derived compounds have antimicrobial activity, colistin is a product of **microbial fermentation**.

Q: Which of the following drugs is not recommended for the treatment of P. falciparum malaria?

Ciprofloxacin. ***Ciprofloxacin*** - **Ciprofloxacin** is an antibiotic that is not effective against **Plasmodium falciparum** and is therefore not used in the treatment of malaria. - While it targets bacterial infections, it lacks the necessary antimalarial activity to clear the parasitic infection. *Quinine* - **Quinine** is an **oral antimalarial drug** that is effective against **P. falciparum**, especially in cases of multidrug resistance. - It works by inhibiting the parasite's ability to detoxify heme, leading to oxidative stress. *Artemether* - **Artemether** is an **artemisinin derivative**, a class of drugs that are highly effective and are the **first-line agents** for treating uncomplicated **P. falciparum malaria**. - It rapidly reduces parasite biomass, particularly in combination with drugs like lumefantrine. *Doxycycline* - **Doxycycline** is a **tetracycline antibiotic** that can be used as an alternative or adjunctive treatment for **P. falciparum malaria**, particularly in areas with resistance to other antimalarials. - It functions by inhibiting protein synthesis in the parasite and is commonly used for both treatment and prophylaxis.

Q: Which antifungal can be used orally but not intravenously?

Griseofulvin. ***Griseofulvin*** - **Griseofulvin** is an oral antifungal agent primarily used for dermatophyte infections [2], and it is **not available** or administered intravenously. - Its mechanism involves binding to **keratin** in newly forming skin, hair, and nails, preventing fungal invasion. *Voriconazole* - **Voriconazole** is a broad-spectrum triazole antifungal that is available in both **oral and intravenous** formulations [1]. - It is often used for invasive aspergillosis and other serious fungal infections [2]. *Amphotericin B* - **Amphotericin B** is a potent antifungal agent administered **intravenously** for severe systemic fungal infections [2]. - It has **poor oral bioavailability** and is not absorbed from the gastrointestinal tract, making it unsuitable for oral systemic therapy. - Oral formulations exist only for **local treatment** of GI candidiasis, not for systemic infections. *None of the options* - This option is incorrect because **griseofulvin** fits the description of being an antifungal that can be used orally but not intravenously.

Q: Which of the following cephalosporins is most commonly associated with drug-induced thrombocytopenia?

Cefoperazone. ***Cefoperazone*** - **Cefoperazone** is most commonly associated with drug-induced thrombocytopenia among the listed cephalosporins. - It contains the **N-methylthiotetrazole (NMTT) side chain**, which is associated with two major hematological complications: - **Hypoprothrombinemia** due to interference with vitamin K metabolism (leading to bleeding) - **Immune-mediated thrombocytopenia** where the drug acts as a hapten, inducing antibody formation against platelets - Other cephalosporins with NMTT side chains (cefamandole, cefotetan, moxalactam) share similar risks. - The dual mechanism of both coagulation factor depletion and platelet destruction makes cefoperazone particularly notable for hematological adverse effects. *Ceftazidime* - **Ceftazidime** is a third-generation cephalosporin that can rarely cause thrombocytopenia through immune-mediated mechanisms. - However, the incidence is **lower compared to cefoperazone** and it lacks the NMTT side chain. - Reports exist but it is not the "most commonly associated" among cephalosporins. *Cefixime* - **Cefixime** is an oral third-generation cephalosporin with a **very low risk** of hematological side effects. - Reports of cefixime-induced thrombocytopenia are **exceedingly rare** and not commonly cited in pharmacology literature. *Cefdinir* - **Cefdinir** is an oral third-generation cephalosporin used for common bacterial infections. - Like cefixime, reports of **cefdinir-induced thrombocytopenia** are extremely rare and not a recognized common adverse effect.

Question 1

Which of the following statements about the primary clinical use of levamisole is true?

Accepted Answer

It is used against ascariasis and ancyclostomiasis

Answer

It has immunomodulator action

Answer

It is the levoisomer of tetramisole

Answer

It can kill strongyloides larvae and adult worms

Question 2

Which compound is primarily responsible for the hepatotoxicity associated with Isoniazid (INH)?

Accepted Answer

INH acetylhydrazine

Answer

INH sulfhydrazine

Answer

INH methylhydrazine

Answer

None of the options

Question 3

Typhoid is treated by all except

Accepted Answer

Erythromycin

Answer

Amikacin

Answer

Ciprofloxacin

Answer

Ceftriaxone

Question 4

Anti-HIV drug used for prevention of vertical transmission?

Accepted Answer

Nevirapine

Answer

Lamivudine

Answer

Efavirenz

Answer

Tenofovir

Question 5

Which of the following can prolong QT interval?

Accepted Answer

Gatifloxacin

Answer

Nalidixic acid

Answer

Pefloxacin

Answer

Ofloxacin

Question 6

Which antibiotic is known to cause irreversible hearing loss?

Accepted Answer

Gentamicin

Answer

Clarithromycin

Answer

Vancomycin

Answer

None of the options

Question 7

Colistin is obtained from ?

Accepted Answer

Bacteria

Answer

Fungi

Answer

Herbs

Answer

Actinomycetes

Question 8

Which of the following drugs is not recommended for the treatment of P. falciparum malaria?

Accepted Answer

Ciprofloxacin

Answer

Artemether

Answer

Doxycycline

Answer

Quinine

Question 9

Which antifungal can be used orally but not intravenously?

Accepted Answer

Griseofulvin

Answer

Voriconazole

Answer

Amphotericin B

Answer

None of the options

Question 10

Which of the following cephalosporins is most commonly associated with drug-induced thrombocytopenia?

Accepted Answer

Cefoperazone

Answer

Cefixime

Answer

Ceftazidime

Answer

Cefdinir

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

On this page

Practice by Chapter

Want unlimited practice?