Antimicrobial Agents — MCQs

A 30-year-old man presents to his primary care physician for pain in his left ankle. The patient states that he was at karate practice when he suddenly felt severe pain in his ankle forcing him to stop. The patient has a past medical history notable for type I diabetes and is currently being treated for an episode of acute bacterial sinusitis with moxifloxacin. The patient recently had to have his insulin dose increased secondary to poorly controlled blood glucose levels. Otherwise, the patient takes ibuprofen for headaches and loratadine for seasonal allergies. Physical exam reveals a young healthy man in no acute distress. Pain is elicited over the Achilles tendon with dorsiflexion of the left foot. Pain is also elicited with plantar flexion of the left foot against resistance. Which of the following is the best next step in management?

Q1329

Drug of choice for nasal carriers of MRSA is:

Q1330

Praziquantel is used for the treatment of

Antimicrobial Agents Indian Medical PG Practice Questions and MCQs

Question 1321: Why does Mycoplasma genitalium show a higher rate of antimicrobial resistance compared to other STI pathogens?

A. Due to plasmid exchange with other bacteria
B. Due to absence of cell wall making beta-lactams ineffective
C. Due to biofilm formation protecting from antibiotics
D. Due to rapid mutation in the 23S rRNA gene (Correct Answer)

Explanation: ***Due to rapid mutation in the 23S rRNA gene*** [1] - *Mycoplasma genitalium* develops **resistance to macrolides**, a primary treatment, through **point mutations in the 23S rRNA gene** [1]. - These mutations alter the ribosomal binding site, preventing macrolide antibiotics from inhibiting **bacterial protein synthesis** [2]. *Due to plasmid exchange with other bacteria* - *Mycoplasma genitalium* **lacks a cell wall** and generally does not engage in significant plasmid exchange, which is a common mechanism for horizontal gene transfer and resistance acquisition in many other bacteria. - While other bacteria acquire resistance through plasmids, this mechanism is **not prominent** in *Mycoplasma genitalium*. *Due to absence of cell wall making beta-lactams ineffective* - The **absence of a cell wall** inherently makes beta-lactam antibiotics ineffective against *Mycoplasma genitalium*, as **beta-lactams target cell wall synthesis**. - However, this is a **natural resistance** and does not explain its higher rate of acquired antimicrobial resistance to other classes of antibiotics, such as macrolides. *Due to biofilm formation protecting from antibiotics* - While **biofilm formation can protect bacteria** from antibiotics, it is not the primary or most notable mechanism explaining the high rate of acquired resistance in *Mycoplasma genitalium*. - The major concern for *M. genitalium* resistance lies in **specific genetic mutations** affecting relevant antibiotic targets.

Question 1322: What is the mechanism of action of acyclovir in treating herpes infections?

A. Inhibits viral reverse transcriptase
B. Prevents viral attachment to host cells
C. Blocks release of mature virions
D. Inhibits viral DNA polymerase after phosphorylation (Correct Answer)

Explanation: ***Inhibits viral DNA polymerase after phosphorylation*** - Acyclovir is a **prodrug** that requires activation by viral thymidine kinase, converting it to acyclovir monophosphate. - Subsequent phosphorylation by cellular enzymes forms acyclovir triphosphate, which then competitively inhibits and **inactivates viral DNA polymerase**, terminating DNA chain synthesis. *Inhibits viral reverse transcriptase* - **Reverse transcriptase inhibitors** are primarily used in the treatment of **HIV infections**, as HIV is a retrovirus that utilizes reverse transcriptase for replication. - Herpesviruses are DNA viruses and their replication does not involve a reverse transcriptase enzyme. *Prevents viral attachment to host cells* - This mechanism is characteristic of some **antiviral drugs** that target viral glycoproteins or host cell receptors to block the initial step of infection. - Acyclovir primarily acts intracellularly once the virus has already entered the host cell. *Blocks release of mature virions* - This mechanism is seen with **neuraminidase inhibitors** used for **influenza**, which prevent the budding and release of new viral particles from infected cells. - Acyclovir's action occurs earlier in the viral replication cycle, specifically at the DNA synthesis stage.

Question 1323: A patient with multiple sexual exposures is diagnosed with gonorrhea. What is the appropriate treatment?

A. Acyclovir
B. Cefixime
C. Doxycycline
D. Ceftriaxone (Correct Answer)

Explanation: ***Ceftriaxone*** - **Ceftriaxone** is the **first-line recommended treatment** for uncomplicated gonorrhea according to **CDC and WHO guidelines**. - Administered as a **single intramuscular injection (500 mg IM)**, it provides highly effective coverage against *Neisseria gonorrhoeae* with minimal resistance. - It works by inhibiting bacterial cell wall synthesis, and is the **gold standard therapy** for gonorrhea treatment. - For patients with multiple sexual exposures, empiric treatment for co-infection with *Chlamydia trachomatis* (doxycycline) should also be considered. *Cefixime* - **Cefixime** was previously used as an oral alternative but is **no longer recommended** as first-line therapy due to **increasing resistance** of *N. gonorrhoeae*. - The CDC removed cefixime from recommended regimens due to **inferior efficacy** compared to ceftriaxone and concerns about treatment failures. - While it is an oral cephalosporin, it is **not appropriate first-line therapy** for gonorrhea. *Doxycycline* - **Doxycycline** is commonly used to treat **co-infection with *Chlamydia trachomatis***, which frequently occurs alongside gonorrhea. - The typical regimen is **100 mg twice daily for 7 days** as adjunctive therapy. - However, doxycycline is **not effective as monotherapy for gonorrhea** and should not be used alone to treat *N. gonorrhoeae* infection. *Acyclovir* - **Acyclovir** is an **antiviral medication** used to treat **herpes simplex virus (HSV)** infections. - It works by inhibiting viral DNA replication and has **no activity against bacterial infections** like gonorrhea. - It would be completely ineffective against *Neisseria gonorrhoeae*.

Question 1324: A child presents with complaints of fever, rash, body ache, and throat ache. He had a history of thorn prick injury a week back. What antibiotics would you give empirically to this child?

A. Amoxicillin+ clavulanate (Correct Answer)
B. Ceftriaxone
C. Vancomycin
D. Meropenem

Explanation: ***Amoxicillin + clavulanate*** - This combination provides **broad-spectrum coverage** against common skin flora including **Staphylococcus aureus**, **Streptococcus species**, and **anaerobes** that can be introduced by thorn prick injuries. - The **beta-lactamase inhibitor (clavulanate)** extends coverage to beta-lactamase producing organisms commonly found in skin infections. - Covers **Streptococcus pyogenes** which could explain the throat ache, making it ideal for this child with both skin infection and pharyngitis symptoms. - Most appropriate **first-line empiric therapy** for pediatric skin and soft tissue infections with systemic symptoms. *Ceftriaxone* - While this **third-generation cephalosporin** has good coverage against many gram-negative bacteria and some gram-positive organisms including **MSSA (methicillin-sensitive S. aureus)**, it is typically **reserved for parenteral therapy** in more severe infections. - For this clinical scenario, amoxicillin-clavulanate is preferred because it provides better **beta-lactamase coverage**, can be given orally, and covers both aerobic and anaerobic organisms relevant to thorn prick injuries. - Would be considered if the patient required **hospitalization** or failed first-line therapy. *Vancomycin* - This antibiotic is primarily used for serious infections caused by **multi-drug resistant gram-positive bacteria**, particularly **methicillin-resistant Staphylococcus aureus (MRSA)**. - Given the history of a thorn prick without specific risk factors for MRSA (no prior MRSA infection, hospital exposure, or failed beta-lactam therapy), there is **no indication for empiric vancomycin use**. - Using vancomycin empirically without specific indication contributes to **antibiotic resistance** and is not guideline-recommended. *Meropenem* - A **carbapenem** antibiotic reserved for **severe, life-threatening infections** caused by multi-drug resistant organisms or in cases of **septic shock** with unknown etiology. - The clinical presentation does not suggest severe sepsis, necrotizing fasciitis, or resistant pathogen requiring such broad coverage. - Empiric use in this scenario would represent **inappropriate antimicrobial stewardship** and promote development of carbapenem-resistant organisms.

Question 1325: Antimicrobial combinations are used in all except

A. Intra abdominal infections
B. Malaria
C. Tuberculosis
D. Gonorrhea (Correct Answer)

Explanation: ***Gonorrhea*** - While **gonorrhea** treatment has evolved to include **dual therapy** (e.g., ceftriaxone + azithromycin), this is primarily for co-treatment of potential Chlamydia co-infection and to combat emerging resistance, given as a **single-session treatment**. - Unlike the other conditions, gonorrhea does not require a **prolonged multi-drug regimen** with true synergy or prevention of resistance development during treatment. - The combination is more about empiric co-coverage and resistance concerns rather than the classic indications for antimicrobial combinations (synergy, preventing resistance emergence during therapy, polymicrobial coverage). - This distinguishes it from conditions requiring extended combination therapy. *Intra-abdominal infections* - Involve **polymicrobial etiology** requiring combination therapy to cover both aerobic (e.g., Enterobacteriaceae) and anaerobic bacteria (e.g., Bacteroides fragilis). - Combination therapy ensures broad-spectrum coverage for mixed infections and prevents treatment failures in complex intra-abdominal sepsis. *Malaria* - **Artemisinin-based combination therapies (ACTs)** are the standard first-line treatment for uncomplicated *Plasmodium falciparum* malaria. - Combination therapy reduces drug resistance risk and improves cure rates by targeting different mechanisms of action against the parasite. *Tuberculosis* - Treatment always involves **multi-drug regimen** (isoniazid, rifampicin, pyrazinamide, ethambutol) to prevent emergence of drug-resistant strains. - Multi-drug therapy is essential because *Mycobacterium tuberculosis* rapidly develops resistance if exposed to single agents during the prolonged treatment course.

Question 1326: Identify the correct 'organism-drug to which it is intrinsically resistant' pair.

A. Candida krusei - Fluconazole (Correct Answer)
B. Candida albicans - Amphotericin B
C. Aspergillus fumigatus - Micafungin
D. Aspergillus niger - Voriconazole

Explanation: ***Candida krusei - Fluconazole*** - **Candida krusei** is intrinsically resistant to **fluconazole** due to reduced affinity of its target enzyme, **lanosterol 14-alpha demethylase**, for the drug. - This resistance is a natural characteristic of the species, meaning it is inherent and not acquired through exposure. *Aspergillus fumigatus - Micafungin* - **Aspergillus fumigatus** is generally susceptible to **micafungin**, an **echinocandin drug** that targets fungal cell wall synthesis. - While resistance can develop, it is not an intrinsic characteristic of *A. fumigatus* to micafungin. *Candida albicans - Amphotericin B* - **Candida albicans** is typically susceptible to **amphotericin B**, a polyene antifungal that binds to ergosterol in the fungal cell membrane. - Intrinsic resistance to amphotericin B in *C. albicans* is rare, though acquired resistance can occur. *Aspergillus niger - Voriconazole* - **Aspergillus niger** is usually susceptible to **voriconazole**, a broad-spectrum triazole antifungal. - There is no known intrinsic resistance of *A. niger* to voriconazole.

Question 1327: A 31-year-old man presents with dysuria and urethral discharge. Gram stain shows intracellular gram-negative diplococci. Local resistance patterns show 28% quinolone resistance. Which of the following most appropriately guides empiric therapy selection?

A. Patient preference
B. Duration of therapy
C. Local antimicrobial susceptibility patterns (Correct Answer)
D. Route of administration
E. Organism identification confirmation

Explanation: ***Local antimicrobial susceptibility patterns*** - Understanding local resistance patterns is crucial for selecting effective empiric therapy, especially with the high quinolone resistance (28%) mentioned. - **Empiric therapy** for suspected **gonorrhea** (suggested by intracellular gram-negative diplococci) must target common resistance mechanisms to ensure initial treatment success. *Patient preference* - While patient preferences can influence adherence, they do not guide the initial choice of antibiotic for a serious infection like gonorrhea, which requires an effective agent. - Clinical efficacy and public health considerations for preventing resistance take precedence over patient preference in selecting empiric therapy. *Duration of therapy* - The duration of therapy is determined *after* an effective antibiotic is chosen and is based on the specific infection and organism; it does not guide the initial selection of the drug itself. - Most gonorrhea treatments are single-dose, but this is a consequence of the chosen drug's efficacy rather than a guiding principle for selection. *Route of administration* - While practical for the patient, the route of administration (e.g., oral vs. intramuscular) is a secondary consideration after an effective agent is identified based on susceptibility. - Many empiric gonorrhea treatments include an intramuscular injection for single-dose efficacy, making route less of a primary guide for selection. *Organism identification confirmation* - Waiting for definitive organism identification and susceptibility testing would delay treatment and is inappropriate for symptomatic gonorrhea, which requires immediate empiric therapy. - The Gram stain already provides strong presumptive evidence, and empiric treatment must be initiated based on likely pathogens and local resistance patterns rather than waiting for culture confirmation.

Question 1328: A 30-year-old man presents to his primary care physician for pain in his left ankle. The patient states that he was at karate practice when he suddenly felt severe pain in his ankle forcing him to stop. The patient has a past medical history notable for type I diabetes and is currently being treated for an episode of acute bacterial sinusitis with moxifloxacin. The patient recently had to have his insulin dose increased secondary to poorly controlled blood glucose levels. Otherwise, the patient takes ibuprofen for headaches and loratadine for seasonal allergies. Physical exam reveals a young healthy man in no acute distress. Pain is elicited over the Achilles tendon with dorsiflexion of the left foot. Pain is also elicited with plantar flexion of the left foot against resistance. Which of the following is the best next step in management?

A. Refrain from athletic activities for 1 to 2 weeks
B. Rehabilitation exercises and activity as tolerated
C. Ibuprofen and rest
D. Change antibiotics and refrain from athletic activities (Correct Answer)

Explanation: The patient is experiencing **Achilles tendonitis**, likely a side effect of **moxifloxacin**, which is known to cause **tendinopathy** and **tendon rupture**, especially in patients with **diabetes** or those initiating **corticosteroids** [1]. **Discontinuation of moxifloxacin** and avoidance of strenuous activities are crucial to prevent further tendon damage, with alternative antibiotics for sinusitis [1]. *Refrain from athletic activities for 1 to 2 weeks* - While **refraining from activity** is important, it is insufficient on its own because the underlying cause (moxifloxacin) would persist, potentially worsening the tendon injury. - This option does not address the need to **change the causative medication**, which is the primary intervention for fluoroquinolone-induced tendinopathy [1]. *Rehabilitation exercises and activity as tolerated* - **Rehabilitation exercises** are typically introduced in later stages of recovery, after the acute inflammation has subsided and the causative agent is removed. - **Activity as tolerated** is inappropriate when there is a high risk of **tendon rupture** due to drug-induced tendinopathy; initial management requires strict rest. *Ibuprofen and rest* - **Ibuprofen** can help with pain and inflammation, but it does not address the underlying **fluoroquinolone-induced tendinopathy**. - While **rest** is important, the continued use of moxifloxacin would still predispose the patient to further tendon injury or rupture, making simply resting an incomplete solution.

Question 1329: Drug of choice for nasal carriers of MRSA is:

A. Linezolid
B. Vancomycin
C. Mupirocin (Correct Answer)
D. Teicoplanin

Explanation: ***Mupirocin*** - **Mupirocin** (Bactroban) is a **topical antibacterial agent** frequently used for the eradication of **nasal colonization with MRSA**. - It is applied directly to the **nares** and works by inhibiting bacterial protein synthesis. *Linezolid* - **Linezolid** is an **oral** or **intravenous antibiotic** used for systemic MRSA infections, not typically for nasal decolonization. - Its use for nasal carriage would be inappropriate due to the risk of systemic side effects and potential for resistance development. *Vancomycin* - **Vancomycin** is a **glycopeptide antibiotic** administered intravenously for severe MRSA infections, not for nasal decolonization. - It has poor oral bioavailability and is not effective as a topical agent for nasal carriage. *Teicoplanin* - **Teicoplanin** is another **glycopeptide antibiotic** similar to vancomycin, used for systemic MRSA infections. - Like vancomycin, it is not used for the topical eradication of nasal MRSA colonization.

Question 1330: Praziquantel is used for the treatment of

A. Schistosomiasis (Correct Answer)
B. Rhinosporidiosis
C. Strongyloidiasis
D. Trichomoniasis

Explanation: ***Schistosomiasis*** - **Praziquantel** is the primary drug for treating all species of **schistosomiasis**, effectively killing adult worms [1], [2]. - It works by increasing the **calcium permeability** of the worm's cells, leading to muscle contraction and paralysis [2]. *Rhinosporidiosis* - **Rhinosporidiosis** is a fungal infection, and its treatment typically involves **surgical excision** of the lesions. - Antifungal agents like **dapsone** may be used as an adjuvant therapy, but praziquantel is not indicated. *Strongyloidiasis* - **Strongyloidiasis** is caused by the nematode *Strongyloides stercoralis*, and the preferred treatment is **ivermectin** [3]. - **Albendazole** is an alternative treatment option, but praziquantel is ineffective against this parasite [2], [3]. *Trichomoniasis* - **Trichomoniasis** is a sexually transmitted infection caused by the protozoan *Trichomonas vaginalis*. - It is effectively treated with **metronidazole** or **tinidazole**, while praziquantel has no activity against this protozoan.

Practice by Chapter

Beta-Lactam Antibiotics

Practice Questions

Aminoglycosides

Practice Questions

Macrolides and Ketolides

Practice Questions

Tetracyclines

Practice Questions

Quinolones

Practice Questions

Sulfonamides and Trimethoprim

Practice Questions

Antimycobacterial Drugs

Practice Questions

Antifungal Agents

Practice Questions

Antiviral Drugs

Practice Questions

Antiparasitic Agents

Practice Questions

Principles of Antimicrobial Selection

Practice Questions

Antimicrobial Resistance

Practice Questions

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