Antimicrobial Agents Practice Questions

Q: Mechanism of action of Oseltamivir?

Neuraminidase inhibitor. ***Neuraminidase inhibitor*** - **Oseltamivir** prevents the release of new influenza virus particles from infected cells by inhibiting **neuraminidase**, an enzyme essential for viral replication. - This inhibition limits the spread of the virus to uninfected cells, thereby reducing the severity and duration of the **flu**. *Inhibitor of protein synthesis* - This mechanism is characteristic of certain **antibiotics** (e.g., tetracyclines, macrolides) or **antitumor agents**, not antiviral medications like oseltamivir. - Inhibiting protein synthesis would interfere with the host cell's vital functions and is not the primary target for influenza antivirals. *Inhibitor of thymidylate synthetase* - **Thymidylate synthetase inhibitors** (e.g., 5-fluorouracil) are primarily used in **cancer chemotherapy** to block DNA synthesis in rapidly dividing cells. - This mechanism is not relevant to the action of oseltamivir against influenza virus. *Pyrimidine analogs* - **Pyrimidine analogs** (e.g., zidovudine, fluorouracil) are drugs that mimic natural pyrimidine bases and interfere with nucleic acid synthesis. - While some antivirals act as nucleoside/nucleotide analogs, this is a broader category, and oseltamivir's specific action is not as a pyrimidine analog.

Q: Which antiretroviral drug also has anti-hepatitis activity?

Tenofovir. ***Tenofovir*** - **Tenofovir** is a nucleotide reverse transcriptase inhibitor (NtRTI) that is highly effective against both **HIV** and **Hepatitis B virus (HBV)**. - It is a **first-line agent** for HBV treatment with a **high barrier to resistance**, making it the preferred choice for dual therapy in HIV/HBV coinfection. - It is FDA-approved for both HIV and HBV treatment and is a key component in antiretroviral therapy (ART) regimens for coinfected patients. *Abacavir* - **Abacavir** is a nucleoside reverse transcriptase inhibitor (NRTI) used for HIV treatment. - It does not have significant activity against **Hepatitis B virus (HBV)** or other hepatitis viruses. *Emtricitabine* - **Emtricitabine** is a nucleoside reverse transcriptase inhibitor (NRTI) that has activity against both **HIV** and **HBV**. - While it is FDA-approved for HBV treatment, it has a **lower barrier to resistance** compared to tenofovir and is less preferred as monotherapy for HBV. - It is commonly used in combination with tenofovir (as in Truvada) for enhanced efficacy in HIV/HBV coinfection. - **Tenofovir remains the best answer** due to its superior resistance profile and status as first-line HBV therapy. *Nevirapine* - **Nevirapine** is a non-nucleoside reverse transcriptase inhibitor (NNRTI) used specifically for **HIV infection**. - It does not demonstrate antiviral activity against **Hepatitis B virus (HBV)** or other forms of viral hepatitis.

Q: What is the primary site of action of amphotericin B?

Plasma membrane. ***Plasma membrane*** - Amphotericin B primarily acts at the **fungal cell membrane**, specifically by binding to **ergosterol**, a sterol essential for fungal membrane integrity. - This binding leads to the formation of **pores** or channels in the membrane, causing leakage of intracellular ions and macromolecules, thus disrupting cellular function and causing cell death. *Cell wall* - The **cell wall** is mainly composed of **chitin** and glucans, which provide structural rigidity to fungal cells. - Amphotericin B does not directly target the fungal cell wall; instead, its action is focused on the underlying **plasma membrane**. *Protein* - Amphotericin B is a **polyene antifungal** medication and is not primarily involved in targeting or inhibiting protein synthesis. - Inhibition of **protein synthesis** is a mechanism seen in certain antibacterial agents (e.g., tetracyclines, macrolides) but not in amphotericin B. *Ribosomes* - **Ribosomes** are responsible for protein synthesis and are not the primary target of amphotericin B. - While disrupting the cell membrane can indirectly affect various cellular processes, including protein synthesis, it is not a direct site of action for this drug.

Q: What is the drug of choice (DOC) for the treatment of subacute sclerosing panencephalitis (SSPE)?

Inosine pranobex. ***Inosine pranobex*** - **Inosine pranobex (Isoprinosine)** is considered the **oral drug of choice** for treating **subacute sclerosing panencephalitis (SSPE)**, particularly in the early stages, as it has shown success in delaying disease progression. - This drug works by **modulating the immune system** and enhancing T-cell function, which helps control the persistent measles virus infection in the CNS. - **Note:** Best outcomes are achieved when inosine pranobex is combined with **intrathecal/intraventricular interferon-alpha**, but as a single oral agent, inosine pranobex is the primary choice. *Abacavir* - **Abacavir** is an **antiretroviral drug (NRTI)** used in the treatment of **HIV infection**. - It inhibits reverse transcriptase and has **no role** in treating measles virus-induced SSPE. *Glatiramer* - **Glatiramer acetate** is an **immunomodulatory drug** used in **multiple sclerosis (MS)**. - It works by mimicking **myelin basic protein** to reduce immune attacks on myelin, but is **not effective** against viral infections like SSPE. *Interferon* - **Interferon-alpha** (particularly **intrathecal/intraventricular** administration) has been used in **SSPE** as **combination therapy** with inosine pranobex, showing improved outcomes. - However, when given systemically alone, it has **significant side effects** and **variable efficacy**. - As a single answer option without specifying the route, **inosine pranobex** is preferred as the primary oral DOC.

Q: In areas with chloroquine-sensitive P. vivax, what is the preferred drug for treating the blood stages?

Chloroquine. ***Correct Option: Chloroquine***- **Chloroquine** remains the **first-line treatment** for **chloroquine-sensitive P. vivax** infections due to its high efficacy and safety profile [1, 2].- It rapidly clears **blood-stage parasites**, alleviating acute symptoms of malaria [3].- In areas where P. vivax remains sensitive, chloroquine is preferred due to low cost, good tolerability, and proven effectiveness [1, 2].*Incorrect Option: Mefloquine*- **Mefloquine** is typically reserved for areas with **chloroquine-resistant P. falciparum** or for prophylaxis in such regions.- Its use is generally avoided when less toxic and equally effective options like chloroquine are available for sensitive strains.- Associated with more neuropsychiatric side effects.*Incorrect Option: Artesunate*- **Artesunate** is an **artemisinin derivative**, primarily used for severe malaria or in areas with **multi-drug resistant P. falciparum**.- While effective, it is not the preferred first-line agent for chloroquine-sensitive P. vivax due to the availability of simpler, equally effective treatments.- Typically used in combination therapy (ACT) for resistant strains.*Incorrect Option: Quinine*- **Quinine** is an older antimalarial, often used for **severe malaria** or in cases of **chloroquine-resistant P. falciparum**.- It has a higher incidence of side effects compared to chloroquine (cinchonism, hypoglycemia) and is not the preferred choice for chloroquine-sensitive P. vivax.- Requires longer treatment duration with more monitoring.

Q: Which of the following medications is not indicated for the treatment or prophylaxis of seasonal influenza?

Acyclovir. ***Acyclovir*** - **Acyclovir** is an antiviral medication specifically used to treat infections caused by **herpes viruses** (e.g., HSV, VZV), not influenza viruses. - It works by inhibiting **viral DNA polymerase**, a mechanism distinct from how anti-influenza drugs act. - **This drug has never been indicated for influenza** - it is the correct answer to this "not indicated" question. *Amantadine* - **Amantadine** is an M2 ion channel inhibitor that **was indicated** for influenza A treatment and prophylaxis. - Although no longer recommended due to widespread **resistance** among circulating influenza strains, it remains a drug that was formally indicated for seasonal influenza. *Rimantadine* - **Rimantadine** is also an M2 ion channel inhibitor, structurally related to amantadine, with a similar mechanism of action. - Like amantadine, it **was indicated** for influenza treatment or prophylaxis but is no longer recommended due to high rates of **resistance** in circulating influenza A viruses. *Oseltamivir* - **Oseltamivir** is a **neuraminidase inhibitor** currently approved and recommended for the treatment and prophylaxis of both influenza A and B. - It reduces viral spread by preventing the release of new virions from infected cells and remains a first-line agent for seasonal influenza.

Q: Which of the following combinations does not show synergistic action?

Penicillin plus tetracycline. ***Penicillin plus tetracycline*** - This combination is generally **antagonistic** or **indifferent**, not synergistic. Penicillin is a cell wall synthesis inhibitor that works best on actively growing bacteria, while tetracycline is a bacteriostatic protein synthesis inhibitor that can reduce bacterial growth, thereby diminishing penicillin's effect. - The combination is usually avoided as the **bacteriostatic action of tetracycline** can counteract the **bactericidal action of penicillin**, leading to reduced efficacy, especially in infections requiring rapid bacterial clearance. *Penicillin plus sulfonamide* - This combination can show synergism in some contexts, particularly as sulfonamides inhibit **folate synthesis**, while penicillin inhibits **cell wall synthesis**. - While not a classic synergistic pair for all infections, their mechanisms of action are distinct, and they can sometimes be used together, although specific synergistic effects are more limited compared to other pairs. *Streptomycin plus penicillin* - This is a classic example of **synergistic action**, particularly in conditions like **enterococcal endocarditis**. - Penicillin damages the bacterial cell wall, allowing **streptomycin** (an aminoglycoside) to more easily penetrate the cell and act on ribosomal targets, leading to enhanced bactericidal effect. *Rifampicin plus dapsone* - This combination is a cornerstone of **multi-drug therapy for leprosy**, demonstrating clear synergy against *Mycobacterium leprae*. - **Rifampicin** inhibits bacterial RNA synthesis, and **dapsone** inhibits folate synthesis, attacking different essential bacterial pathways which, when combined, are more effective and reduce the development of resistance.

Q: Idoxuridine is used for treatment of?

HSV. ***HSV*** - **Idoxuridine** is a **pyrimidine analog** that inhibits viral DNA synthesis, making it effective against **herpes simplex virus (HSV)** infections, particularly **herpes keratitis** (ophthalmic use). - Its mechanism involves being incorporated into viral DNA, leading to errors in replication and transcription. - It is applied **topically** for ocular HSV infections due to systemic toxicity concerns. *Influenza* - **Idoxuridine** is not active against **influenza viruses**. - **Antiviral drugs** like **oseltamivir** or **zanamivir** are typically used for influenza treatment. *RSV* - **Idoxuridine** is not indicated for the treatment of **respiratory syncytial virus (RSV)**. - **Ribavirin** is the primary antiviral agent used for severe RSV infections, especially in immunocompromised patients. *HIV* - **Idoxuridine** has no significant activity against **human immunodeficiency virus (HIV)**. - **Antiretroviral therapy (ART)**, a combination of drugs targeting various stages of the HIV life cycle, is used for HIV treatment.

Q: Thymidine is responsible for resistance to which antibiotic ?

Sulfonamide. ***Sulfonamide*** - **Thymidine** can contribute to **sulfonamide resistance** because sulfonamides interfere with **folate metabolism** and the subsequent synthesis of purines and pyrimidines, including thymidine. - An excess of thymidine can bypass the metabolic block caused by sulfonamides, allowing bacteria to continue DNA synthesis and grow. *Erythromycin* - **Erythromycin** resistance is primarily mediated by **methylation of ribosomal RNA**, which prevents the antibiotic from binding to the 50S ribosomal subunit. - It does not directly involve thymidine or the folate synthesis pathway. *Tetracycline* - Resistance to **tetracyclines** is commonly due to **efflux pumps** that actively pump the drug out of the bacterial cell or **ribosomal protection proteins** that prevent tetracycline binding. - Thymidine production or metabolism is not a mechanism of tetracycline resistance. *Nitrofurantoin* - **Nitrofurantoin** resistance typically involves **mutations** in bacterial enzymes (like **nitrofuran reductase**) that are responsible for activating the drug into its active form. - These mutations prevent the drug from becoming bactericidal, and thymidine does not play a role in this mechanism.

Question 1

Mechanism of action of Oseltamivir?

Accepted Answer

Neuraminidase inhibitor

Answer

Inhibitor of protein synthesis

Answer

Inhibitor of thymidylate synthetase

Answer

Pyrimidine analogs

Question 2

Which antiretroviral drug also has anti-hepatitis activity?

Accepted Answer

Tenofovir

Answer

Abacavir

Answer

Nevirapine

Answer

Emtricitabine

Question 3

What is the primary site of action of amphotericin B?

Accepted Answer

Plasma membrane

Answer

Cell wall

Answer

Protein

Answer

Ribosomes

Question 4

Imipenem, a newer antibiotic with a broad antibacterial spectrum, is co-administered with cilastatin. What is the primary reason for this combination?

Accepted Answer

Cilastatin prevents the degradation of imipenem by inhibiting an enzyme in the kidneys.

Answer

Cilastatin enhances the gastrointestinal absorption of imipenem.

Answer

Cilastatin inhibits the beta-lactamase enzyme that degrades imipenem.

Answer

The combination of antibiotics is synergistic against Pseudomonas species.

Question 5

What is the drug of choice (DOC) for the treatment of subacute sclerosing panencephalitis (SSPE)?

Accepted Answer

Inosine pranobex

Answer

Abacavir

Answer

Glatiramer

Answer

Interferon

Question 6

In areas with chloroquine-sensitive P. vivax, what is the preferred drug for treating the blood stages?

Accepted Answer

Chloroquine

Answer

Mefloquine

Answer

Artesunate

Answer

Quinine

Question 7

Which of the following medications is not indicated for the treatment or prophylaxis of seasonal influenza?

Accepted Answer

Acyclovir

Answer

Amantadine

Answer

Rimantadine

Answer

Oseltamivir

Question 8

Which of the following combinations does not show synergistic action?

Accepted Answer

Penicillin plus tetracycline

Answer

Streptomycin plus penicillin

Answer

Rifampicin plus dapsone

Answer

Penicillin plus sulfonamide

Question 9

Idoxuridine is used for treatment of?

Accepted Answer

HSV

Answer

Influenza

Answer

RSV

Answer

HIV

Question 10

Thymidine is responsible for resistance to which antibiotic ?

Accepted Answer

Sulfonamide

Answer

Erythromycin

Answer

Tetracycline

Answer

Nitrofurantoin

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

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