Antimicrobial Agents Practice Questions

Q: What is the drug of choice for MRSA infection?

Vancomycin. ***Vancomycin*** - **Vancomycin** is the **drug of choice** for **methicillin-resistant Staphylococcus aureus (MRSA)** infections due to its activity against the resistant strain. - It works by inhibiting cell wall synthesis, targeting the **D-Ala-D-Ala** precursor in peptidoglycan. *Ciprofloxacin* - **Ciprofloxacin** is a **fluoroquinolone antibiotic** that is generally ineffective against **MRSA**. - MRSA strains are typically **resistant to ciprofloxacin** and other fluoroquinolones. *Oxacillin* - **Oxacillin** is a **beta-lactam antibiotic** in the penicillin family, specifically used for **methicillin-sensitive Staphylococcus aureus (MSSA)** infections. - It is **ineffective against MRSA** because MRSA possesses the *mecA* gene, encoding an altered penicillin-binding protein (PBP2a) that renders beta-lactams inactive. *Clindamycin* - **Clindamycin** can be used for **MRSA infections**, but it is generally reserved for **milder localized infections** or in specific cases based on susceptibility testing. - Its use often requires **D-test** to rule out **inducible clindamycin resistance**, which can lead to treatment failure.

Q: A 3-week-old infant presents with a cough and sore throat. The mother reports that the infant develops a paroxysm of cough followed by apnea. The total leucocyte count is >50,000 cells/μL. Based on these symptoms, which of the following drugs is the most appropriate treatment for this patient?

Azithromycin. ***Azithromycin*** - This infant's symptoms are highly suggestive of **pertussis** (whooping cough), characterized by **paroxysmal coughs** followed by **apnea** in young infants, along with **marked leukocytosis**. - **Macrolides** are the treatment of choice due to their effectiveness against *Bordetella pertussis*; **azithromycin** is preferred in infants due to better tolerability and a shorter course compared to erythromycin. *Amoxicillin* - **Amoxicillin** is a penicillin-class antibiotic primarily effective against various bacterial respiratory infections, but it has **no activity against *Bordetella pertussis***. - Using amoxicillin for pertussis would lead to **treatment failure** and a worsening of the infant's condition. *Cotrimoxazole* - While **cotrimoxazole** (trimethoprim-sulfamethoxazole) can be used as an alternative for pertussis in patients **allergic to macrolides**, it is **not the first-line treatment** in infants. - It carries a risk of **kernicterus** in newborns and young infants due to displacement of bilirubin from albumin, so it is generally avoided. *Erythromycin* - **Erythromycin** is a macrolide and is effective against *Bordetella pertussis*, but it is **associated with a higher incidence of infantile hypertrophic pyloric stenosis** when given to young infants. - Due to this adverse effect, **azithromycin** is generally preferred over erythromycin in infants for pertussis treatment.

Q: 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?

DNA gyrase inhibition. ***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**.

Q: Which fluoroquinolone is contraindicated in patients with liver disease?

Pefloxacin. ***Pefloxacin*** - **Pefloxacin** is primarily metabolized by the **liver**, and its accumulation due to hepatic impairment can lead to increased toxicity and adverse effects, making it contraindicated. - Patients with **severe liver disease** are at a higher risk of experiencing elevated drug levels, leading to complications like **tendinopathy**, **CNS side effects**, or **hepatotoxicity**. *Levofloxacin* - **Levofloxacin** is predominantly excreted by the **kidneys** and only minimally metabolized by the liver, making it generally safer in patients with hepatic impairment. - While dose adjustments may be necessary in **renal dysfunction**, liver disease typically does not require significant modifications. *Ofloxacin* - **Ofloxacin** elimination is primarily **renal**, with little hepatic metabolism, thus it is generally considered safe for use in patients with liver disease. - It does not undergo extensive biotransformation in the liver, minimizing the risk of accumulation in individuals with impaired hepatic function. *Lomefloxacin* - **Lomefloxacin** is relatively safe in patients with liver disease as it is predominantly eliminated renally, similar to levofloxacin and ofloxacin. - Its metabolic pathway does not involve significant hepatic processing, reducing the concern for toxicity in individuals with compromised liver function.

Q: Drug of choice for invasive aspergillosis is

Voriconazole. ***Voriconazole*** - **Voriconazole** is the **first-line drug of choice** for the treatment of **invasive aspergillosis** due to its superior efficacy and good CNS penetration compared to other antifungals. - It works by inhibiting the fungal enzyme **14-alpha-demethylase**, disrupting ergosterol synthesis in the fungal cell membrane. *Posaconazole* - **Posaconazole** is a broad-spectrum triazole antifungal, primarily used for **prophylaxis** of invasive fungal infections in high-risk patients. - While it has activity against *Aspergillus*, it is generally considered a **second-line agent** for treatment or for salvage therapy if voriconazole fails. *Liposomal AMB* - **Liposomal amphotericin B (AMB)** is an effective antifungal for invasive aspergillosis, particularly in patients who **cannot tolerate voriconazole** or have contraindications. - It is often considered a **second-line or alternative therapy** rather than the first-line drug of choice. *Caspofungin* - **Caspofungin** is an **echinocandin** antifungal that inhibits the synthesis of **beta-(1,3)-D-glucan**, a crucial component of the fungal cell wall. - While active against *Aspergillus*, it is typically used as **salvage therapy** or in combination with other antifungals for invasive aspergillosis, not as a monotherapy first-line drug.

Q: What is the Drug of Choice (DOC) for Onychomycosis?

Terbinafine. ***Terbinafine*** - **Terbinafine** is considered the **drug of choice** for **onychomycosis** due to its potent fungicidal activity against **dermatophytes**, which are the most common cause of nail infections [1]. - It accumulates in the nail plate at therapeutic levels, leading to high cure rates and a relatively good safety profile [2]. *Fluconazole* - While effective against some fungi, **fluconazole** is primarily fungistatic and generally less effective against dermatophytes compared to terbinafine for onychomycosis, resulting in lower cure rates [1]. - It is often preferred for **mucocutaneous candidiasis** and other systemic fungal infections [1]. *Itraconazole* - **Itraconazole** is an alternative for onychomycosis, often administered in pulse doses, but it can have more significant drug interactions and a higher risk of hepatic toxicity compared to terbinafine [1]. - Its efficacy against dermatophytes is comparable to terbinafine, but its side effect profile makes it a second-line option [1]. *Nystatin* - **Nystatin** is a topical antifungal effective primarily against **Candida species**, and is not effective against **dermatophytes**, which are the main pathogens in onychomycosis. - It is typically used for mucocutaneous candidiasis, such as oral thrush or vaginal yeast infections, and is not absorbed systemically.

Q: What is the drug of choice for treating isosporiasis?

Co-trimoxazole. ***Co-trimoxazole*** - **Co-trimoxazole** (trimethoprim-sulfamethoxazole) is the **drug of choice** for treating **isosporiasis** (*Cystoisospora belli*, formerly *Isospora belli*), particularly in both immunocompetent and immunocompromised individuals. - Its mechanism of action involves inhibiting **folic acid synthesis** in the parasite through sequential blockade of the folate pathway, leading to its death. - Standard dose: **TMP 160 mg/SMX 800 mg QID for 10 days** in immunocompetent patients; HIV patients may require longer therapy and secondary prophylaxis. *Penicillin G* - **Penicillin G** is an **antibiotic** primarily used to treat bacterial infections, such as those caused by Streptococcus and Staphylococcus species. - It has **no activity** against **Isospora belli**, which is a parasitic protozoan infection. *Benzathine penicillin* - **Benzathine penicillin** is a **long-acting form of penicillin** commonly used for syphilis and rheumatic fever prevention due to its prolonged release. - Like penicillin G, it is an antibacterial agent and is **ineffective against parasitic infections** like isosporiasis. *Albendazole* - **Albendazole** is an **antihelminthic drug** used to treat a variety of helminth infections, such as hookworm, roundworm, and tapeworm. - It is **not effective** against **Isospora belli**, which is a protozoan parasite, not a helminth.

Q: Which fluoroquinolone has the maximum bioavailability?

Levofloxacin. ***Levofloxacin*** - **Levofloxacin** exhibits high oral bioavailability, approximately 99%, meaning nearly all of the administered dose reaches systemic circulation [1]. - This high bioavailability allows for seamless transition from intravenous to oral administration without significant changes in drug exposure [1]. *Moxifloxacin* - **Moxifloxacin** has a high bioavailability of approximately 90%, which is slightly lower than levofloxacin's almost complete absorption [1]. - While excellent, it is not the absolute highest among fluoroquinolones. *Gatifloxacin* - **Gatifloxacin** has good oral bioavailability, around 96%, but it is still generally considered slightly less than that of levofloxacin [1]. - This difference, though small, makes levofloxacin the one with the highest overall bioavailability. *Ciprofloxacin* - **Ciprofloxacin** has the lowest oral bioavailability among the listed fluoroquinolones, ranging from 70% to 80% [1]. - Its absorption can be significantly impaired by co-administration with multivalent cations, leading to reduced systemic concentrations.

Q: Carbapenem which has a tendency to cause maximum seizures?

Imipenem. ***Imipenem*** - **Imipenem** is associated with the highest risk of **seizures** among the carbapenems, particularly in patients with **renal impairment**, pre-existing **CNS disorders**, or high doses. - Its high affinity for **GABA-A receptors** in the central nervous system is thought to contribute to its proconvulsant effects. *Ertapenem* - While all carbapenems carry some risk of seizures, **ertapenem** has a **lower incidence** compared to imipenem. - It is often favored in patients without CNS infections or severe renal dysfunction due to its once-daily dosing. *Doripenem* - **Doripenem** also has a relatively **low risk of seizures** compared to imipenem. - It is generally well-tolerated, with side effects similar to other carbapenems but at a reduced frequency for CNS events. *Meropenem* - **Meropenem** is known to have a **lower seizure potential** than imipenem, making it a preferred choice for patients with a history of seizures or those with CNS infections. - Its **reduced affinity** for GABA-A receptors contributes to its better CNS tolerability.

Q: What is the drug of choice for treating Cyclosporiasis?

Trimethoprim-sulfamethoxazole combination. ***Trimethoprim-sulfamethoxazole combination*** - **Trimethoprim-sulfamethoxazole (TMP-SMX)** is the highly effective and **drug of choice** for treating **Cyclosporiasis**, particularly in both immunocompetent and immunocompromised individuals. - It is administered orally and works by inhibiting folic acid synthesis in the parasite. *Paromomycin* - **Paromomycin** is an aminoglycoside antibiotic primarily used for treating intestinal amebiasis and cryptosporidiosis, but it is **not effective** against Cyclosporiasis. - It exhibits poor systemic absorption and thus primarily acts within the gastrointestinal tract. *Metronidazole* - **Metronidazole** is commonly used to treat infections caused by anaerobic bacteria and certain parasites like *Giardia* and *Entamoeba histolytica*, but it is **ineffective** against *Cyclospora cayetanensis*. - Its mechanism of action involves disrupting DNA and protein synthesis in susceptible organisms. *Cyclosporin* - **Cyclosporin** is an immunosuppressant drug used to prevent organ transplant rejection and treat autoimmune diseases, and it has **no antiparasitic activity** against *Cyclospora*. - Its primary function is to inhibit T-lymphocyte activation.

Question 1

What is the drug of choice for MRSA infection?

Accepted Answer

Vancomycin

Answer

Ciprofloxacin

Answer

Oxacillin

Answer

Clindamycin

Question 2

A 3-week-old infant presents with a cough and sore throat. The mother reports that the infant develops a paroxysm of cough followed by apnea. The total leucocyte count is >50,000 cells/μL. Based on these symptoms, which of the following drugs is the most appropriate treatment for this patient?

Accepted Answer

Azithromycin

Answer

Amoxicillin

Answer

Cotrimoxazole

Answer

Erythromycin

Question 3

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?

Accepted Answer

DNA gyrase inhibition

Answer

Ribosomal inhibition

Answer

Cell wall synthesis

Answer

Inhibition of folic acid synthesis

Question 4

Which fluoroquinolone is contraindicated in patients with liver disease?

Accepted Answer

Pefloxacin

Answer

Ofloxacin

Answer

Lomefloxacin

Answer

Levofloxacin

Question 5

Drug of choice for invasive aspergillosis is

Accepted Answer

Voriconazole

Answer

Posaconazole

Answer

Liposomal AMB

Answer

Caspofungin

Question 6

What is the Drug of Choice (DOC) for Onychomycosis?

Accepted Answer

Terbinafine

Answer

Fluconazole

Answer

Itraconazole

Answer

Nystatin

Question 7

What is the drug of choice for treating isosporiasis?

Accepted Answer

Co-trimoxazole

Answer

Penicillin G

Answer

Benzathine penicillin

Answer

Albendazole

Question 8

Which fluoroquinolone has the maximum bioavailability?

Accepted Answer

Levofloxacin

Answer

Gatifloxacin

Answer

Ciprofloxacin

Answer

Moxifloxacin

Question 9

Carbapenem which has a tendency to cause maximum seizures?

Accepted Answer

Imipenem

Answer

Ertapenem

Answer

Doripenem

Answer

Meropenem

Question 10

What is the drug of choice for treating Cyclosporiasis?

Accepted Answer

Trimethoprim-sulfamethoxazole combination

Answer

Paromomycin

Answer

Metronidazole

Answer

Cyclosporin

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

On this page

Practice by Chapter

Want unlimited practice?