Antimicrobial Agents — MCQs

Antimicrobial Agents Indian Medical PG Practice Questions and MCQs

Question 511: Which drug, in a single oral dose, provides clinical cure for uncomplicated malaria caused by chloroquine-sensitive or resistant Plasmodium Falciparum, as well as Plasmodium Vivax?

A. Quinine
B. Mefloquine (Correct Answer)
C. Artesunate
D. Proguanil

Explanation: **Explanation:** The correct answer is **Mefloquine**. Mefloquine is a quinoline-methanol derivative characterized by an exceptionally long elimination half-life (approximately 2–3 weeks). This pharmacological property allows it to maintain therapeutic blood levels for a prolonged duration, making it effective as a **single oral dose (15 mg/kg)** for the clinical cure of uncomplicated malaria. It is highly effective against both *P. falciparum* (including chloroquine-resistant strains) and *P. vivax* by acting as a potent blood schizonticide. **Analysis of Incorrect Options:** * **Quinine:** While effective against resistant *P. falciparum*, it has a short half-life and requires a 7-day course (TID dosing). It is never used as a single-dose treatment due to poor compliance and toxicity (Cinchonism). * **Artesunate:** As an Artemisinin derivative, it has a very short half-life (approx. 45 mins). Monotherapy requires at least 5–7 days of treatment to prevent recrudescence; therefore, it is always used in combination (ACT) over 3 days. * **Proguanil:** This is a slow-acting schizonticide primarily used for prophylaxis in combination with Atovaquone. It is not used as a single-dose clinical cure for acute malaria. **High-Yield NEET-PG Pearls:** * **Mechanism:** Mefloquine acts by inhibiting heme polymerization, leading to toxic heme accumulation within the parasite. * **Contraindications:** It is strictly contraindicated in patients with a history of **epilepsy** or **psychiatric disorders** (due to neuropsychiatric side effects like hallucinations and anxiety). * **Prophylaxis:** It is the drug of choice for malaria prophylaxis in travelers to chloroquine-resistant areas (dosed weekly). * **Pregnancy:** It is considered safe in the second and third trimesters.

Question 512: What is the recommended treatment for granuloma inguinale?

A. Tetracycline
B. Azithromycin (Correct Answer)
C. Clarithromycin
D. Streptomycin

Explanation: **Explanation:** **Granuloma Inguinale (Donovanosis)** is a chronic bacterial infection caused by the Gram-negative intracellular organism *Klebsiella granulomatis*. It is characterized by painless, beefy-red, vascular ulcerative lesions that bleed easily on contact. **Why Azithromycin is correct:** According to the current **CDC and WHO guidelines**, **Azithromycin (1g orally once a week or 500mg daily) for at least 3 weeks** is the first-line treatment of choice. It is preferred due to its high intracellular concentration, long half-life, and superior efficacy in achieving complete healing of the lesions compared to older regimens. Treatment must be continued until all lesions have completely epithelialized. **Analysis of Incorrect Options:** * **A. Tetracycline:** While Doxycycline (a tetracycline) is a recommended alternative, it is no longer the first-line agent due to the superior dosing convenience and safety profile of Azithromycin. * **C. Clarithromycin:** Although it belongs to the same Macrolide class as Azithromycin, it is not the standard protocol for Donovanosis and requires more frequent dosing. * **D. Streptomycin:** This was historically used but is now obsolete for this condition due to the risk of ototoxicity, nephrotoxicity, and the requirement for parenteral administration. **High-Yield Clinical Pearls for NEET-PG:** * **Pathognomonic Sign:** Presence of **Donovan bodies** (safety-pin appearance) within macrophages on a Giemsa or Wright stain. * **Clinical Presentation:** "Painless but progressive" ulcers; pseudobuboes (inguinal swelling due to granulation tissue, not lymphadenopathy). * **Alternative Regimens:** Doxycycline (100mg BID), Erythromycin, or Trimethoprim-Sulfamethoxazole. * **Pregnancy:** Azithromycin remains the drug of choice for pregnant women with Donovanosis.

Question 513: Which of the following antitubercular drugs is associated with hypothyroidism?

A. Rifampicin
B. Pyrazinamide
C. Ethionamide (Correct Answer)
D. Streptomycin

Explanation: **Explanation:** **Ethionamide** is a second-line antitubercular drug (a thioamide derivative) that is structurally related to **Methimazole**. Its primary endocrine side effect is **hypothyroidism**. It interferes with iodine organification and the synthesis of thyroid hormones (T3 and T4), leading to a compensatory rise in Thyroid Stimulating Hormone (TSH) and potential goiter formation. This effect is reversible upon discontinuation of the drug but may require levothyroxine supplementation if the drug must be continued. **Analysis of Incorrect Options:** * **Rifampicin:** Known for being a potent **microsomal enzyme inducer**. While it can accelerate the metabolism of levothyroxine (requiring dose adjustments in patients already on thyroid replacement), it does not inherently cause hypothyroidism. Its classic side effect is orange-red discoloration of body fluids. * **Pyrazinamide:** Its most significant side effects are **hepatotoxicity** and **hyperuricemia** (due to inhibition of uric acid excretion), which can precipitate acute gouty arthritis. It has no effect on thyroid function. * **Streptomycin:** An aminoglycoside primarily associated with **ototoxicity** (vestibular more than cochlear) and **nephrotoxicity**. It does not interfere with the endocrine system. **High-Yield Clinical Pearls for NEET-PG:** * **PAS (Para-aminosalicylic acid):** Another second-line ATT drug that also causes hypothyroidism. When used together with Ethionamide, the risk of hypothyroidism is significantly increased. * **Ethionamide Side Effects:** Intense GI irritation (metallic taste, nausea, vomiting) and peripheral neuropathy (prevented by Pyridoxine). * **Monitoring:** Patients on Ethionamide or PAS should have their TSH levels monitored every 3–6 months.

Question 514: Which anti-influenza drug is administered via inhalation?

A. Amantadine
B. Oseltamivir
C. Zanamivir (Correct Answer)
D. Rimantadine

Explanation: ### Explanation **Correct Option: C. Zanamivir** Zanamivir is a **Neuraminidase Inhibitor** effective against both Influenza A and B. It is a highly polar compound with poor oral bioavailability (<5%). To achieve therapeutic concentrations directly at the site of infection (the respiratory tract), it is formulated as a dry powder for **oral inhalation** using a "Diskhaler" device. By inhibiting neuraminidase, it prevents the release of new virions from infected host cells, thereby limiting the spread of the virus. **Analysis of Incorrect Options:** * **A & D. Amantadine and Rimantadine:** These are M2 ion channel blockers (Adamantanes) that inhibit the uncoating of Influenza A. Both are administered **orally**. Due to widespread resistance, they are no longer recommended for routine clinical use. * **B. Oseltamivir:** While also a Neuraminidase Inhibitor like Zanamivir, Oseltamivir is a prodrug designed for **oral administration**. It is the most commonly used systemic treatment for influenza. **High-Yield Clinical Pearls for NEET-PG:** * **Contraindication:** Because Zanamivir is inhaled, it can cause bronchospasm. It is strictly **contraindicated in patients with underlying airway diseases** like Asthma or COPD. * **Baloxavir Marboxil:** A newer, single-dose **oral** drug that inhibits the "cap-snatching" endonuclease activity of the viral RNA polymerase. * **Peramivir:** The only Neuraminidase Inhibitor administered via **intravenous (IV)** injection, reserved for severe or hospitalized cases. * **Timing:** For maximum efficacy, all anti-influenza drugs should ideally be started within **48 hours** of symptom onset.

Question 515: Which of the following drugs is active against Pseudomonas?

A. Ceftriaxone
B. Piperacillin-tazobactam (Correct Answer)
C. Ampicillin
D. Cefalexin

Explanation: **Explanation:** The correct answer is **Piperacillin-tazobactam**. **1. Why Piperacillin-tazobactam is correct:** Piperacillin is an **extended-spectrum penicillin** (specifically an antipseudomonal penicillin). It is designed to penetrate the outer membrane of Gram-negative bacteria like *Pseudomonas aeruginosa*. When combined with Tazobactam (a beta-lactamase inhibitor), its spectrum is further broadened to cover many beta-lactamase-producing organisms. It remains a first-line agent for nosocomial infections where *Pseudomonas* is suspected. **2. Why the other options are incorrect:** * **Ceftriaxone (Option A):** While it is a potent 3rd-generation cephalosporin with excellent Gram-negative coverage, it is a classic "hole" in its spectrum—it has **no activity** against *Pseudomonas*. * **Ampicillin (Option B):** This is an aminopenicillin. It is effective against certain Gram-positives and some Gram-negatives (like *E. coli* or *Proteus*), but it is easily degraded by staphylococcal penicillinases and lacks the structural features to tackle *Pseudomonas*. * **Cefalexin (Option D):** This is a 1st-generation cephalosporin. Its coverage is primarily limited to Gram-positive cocci and a few urinary tract Gram-negatives; it has no role in treating *Pseudomonas*. **3. High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Antipseudomonal Penicillins:** "Takes Care of Pseudomonas" (**T**icarcillin, **C**arbenicillin, **P**iperacillin). * **Cephalosporins active against Pseudomonas:** Ceftazidime (3rd gen) and Cefepime (4th gen). * **Carbapenems:** Imipenem, Meropenem, and Doripenem are active, but **Ertapenem** is the exception (it has no antipseudomonal activity). * **Monobactams:** Aztreonam is a key antipseudomonal agent, especially in patients with penicillin allergies.

Question 516: Which of the following statements about cefepime is true?

A. It is a 4th generation cephalosporin (Correct Answer)
B. Once a day dosing is given
C. It is not active against Pseudomonas
D. It is a prodrug

Explanation: **Cefepime** is a parenteral, broad-spectrum antibiotic classified as a **4th generation cephalosporin** [1]. It is characterized by its "zwitterionic" structure, which allows it to penetrate the outer membrane of Gram-negative bacteria rapidly and resist inactivation by many beta-lactamases (including AmpC) [1]. * **Option A (Correct):** Cefepime (along with Cefpirome) belongs to the 4th generation [1]. These drugs combine the extended Gram-negative coverage of the 3rd generation with the enhanced Gram-positive coverage (especially against *Staphylococci*) of the 1st generation. * **Option B (Incorrect):** Cefepime has a half-life of approximately 2 hours. It requires **twice-daily (q12h)** or thrice-daily dosing, not once-daily. (Note: Ceftriaxone is the cephalosporin famous for once-daily dosing). * **Option C (Incorrect):** Cefepime has **excellent activity against *Pseudomonas aeruginosa***. This is a defining feature of 4th generation cephalosporins, making them vital for treating nosocomial infections and febrile neutropenia [1]. * **Option D (Incorrect):** Cefepime is an active drug administered intravenously or intramuscularly; it is **not a prodrug**. (Example of a cephalosporin prodrug: Cefuroxime axetil or Ceftaroline fosamil). **High-Yield Clinical Pearls for NEET-PG:** * **Spectrum:** Think of Cefepime as "Ceftazidime (anti-pseudomonal) + Cefotaxime (Gram-positive activity)." * **Resistance:** It is highly resistant to hydrolysis by **chromosomal AmpC beta-lactamases**, making it superior to 3rd generation agents for *Enterobacter* infections [1]. * **Adverse Effect:** A unique high-yield side effect of Cefepime is **neurotoxicity** (altered mental status, seizures), especially in patients with renal impairment due to its ability to cross the blood-brain barrier and antagonize GABA.

Question 517: Regarding newer formulations of amphotericin B, which of the following statements is accurate?

A. Amphotericin B colloidal dispersion causes fewer infusion-related reactions than conventional amphotericin B.
B. They are more effective in fungal infections than conventional preparations because they increase tissue uptake of amphotericin B.
C. They have decreased systemic toxicity. (Correct Answer)
D. They have a wider spectrum of antifungal activity than conventional formulations of amphotericin B.

Explanation: **Explanation:** Amphotericin B is a potent antifungal that binds to ergosterol in fungal cell membranes. However, its use is limited by significant toxicity, particularly nephrotoxicity, due to its ability to bind to cholesterol in human cell membranes. **Why Option C is Correct:** The primary rationale for developing lipid-based formulations (Liposomal Amphotericin B, Lipid Complex, and Colloidal Dispersion) is to **reduce systemic toxicity**, specifically **nephrotoxicity**. In these formulations, the drug is encapsulated in lipid vehicles. These lipids act as a "reservoir," preferentially delivering the drug to the reticuloendothelial system (liver and spleen) and fungal cells, thereby reducing the exposure of the drug to the renal tubules. **Analysis of Incorrect Options:** * **Option A:** Amphotericin B Colloidal Dispersion (ABCD) is notorious for causing **more** (or similar) acute infusion-related reactions (fever, chills, rigors) compared to the conventional deoxycholate form. Only the Liposomal form (AmBisome) significantly reduces these reactions. * **Option B:** Lipid formulations are **not more effective** than conventional Amphotericin B. Their efficacy is comparable; their advantage lies solely in their improved safety profile, allowing for higher dosing if necessary. * **Option D:** The antifungal spectrum remains **identical** to conventional Amphotericin B, as the active pharmaceutical ingredient is the same. **NEET-PG High-Yield Pearls:** * **Dose-limiting toxicity:** Nephrotoxicity (causes renal tubular acidosis Type 1 and hypokalemia). * **Liposomal Amphotericin B (AmBisome):** The safest formulation with the least nephrotoxicity and fewest infusion reactions. * **Pre-medication:** To prevent infusion reactions, patients are often given antipyretics, antihistamines, or hydrocortisone. * **Saline Loading:** Administering 1 liter of normal saline before the infusion helps reduce the risk of nephrotoxicity.

Question 518: Which drug used in tuberculosis is known to be hepatotoxic?

A. Isoniazid (Correct Answer)
B. Streptomycin
C. Kanamycin
D. Ethambutol

Explanation: **Explanation:** **Isoniazid (INH)** is a primary first-line antitubercular drug (ATD) and is a well-known cause of drug-induced liver injury (DILI). The hepatotoxicity is primarily attributed to its metabolite, **acetylhydrazine**, which is produced via the N-acetylation pathway. This metabolite acts as a reactive intermediate that causes hepatocellular necrosis. The risk is higher in "slow acetylators," older patients, and those with pre-existing liver disease or concurrent alcohol use. **Analysis of Incorrect Options:** * **Streptomycin & Kanamycin (Options B & C):** These are aminoglycosides. Their primary toxicities are **ototoxicity** (vestibulocochlear nerve damage) and **nephrotoxicity** (acute tubular necrosis). They are not associated with hepatotoxicity. * **Ethambutol (Option D):** This drug is unique among first-line ATDs for being non-hepatotoxic. Its classic side effect is **optic neuritis**, leading to decreased visual acuity and red-green color blindness. **Clinical Pearls for NEET-PG:** * **Hepatotoxic ATDs:** Remember the mnemonic **"RIP"** (Rifampicin, Isoniazid, and Pyrazinamide). Among these, **Pyrazinamide** is considered the most hepatotoxic, while **Rifampicin** is a potent enzyme inducer that can potentiate the toxicity of INH. * **Non-Hepatotoxic ATDs:** Ethambutol and Streptomycin are the safest options when treating a patient with pre-existing liver dysfunction. * **Monitoring:** If serum transaminases (AST/ALT) rise to >3 times the upper limit of normal (ULN) with symptoms, or >5 times ULN without symptoms, hepatotoxic ATDs should be temporarily discontinued.

Question 519: Ethambutol should be used very cautiously in childhood tuberculosis due to which of its side effects?

A. Ocular toxicity (Correct Answer)
B. Renal damage
C. Hepatotoxicity
D. Neurotoxicity

Explanation: **Explanation:** **Ethambutol** is a bacteriostatic first-line antitubercular drug (ATD) that inhibits the enzyme arabinosyltransferase, thereby interfering with cell wall synthesis. **Why Ocular Toxicity is the Correct Answer:** The most significant dose-dependent side effect of Ethambutol is **Retrobulbar Neuritis**. This manifests as a decrease in visual acuity, central scotoma, and **loss of red-green color discrimination**. In young children (typically under 5–6 years), it is extremely difficult to perform reliable subjective visual acuity or color vision testing. Because the child cannot report early visual changes, the toxicity may progress to irreversible damage before it is detected. Therefore, it is used with extreme caution or avoided in very young children unless necessary. **Why Other Options are Incorrect:** * **Renal Damage:** While Ethambutol is excreted via the kidneys and requires dose adjustment in renal failure, it is not primarily nephrotoxic. * **Hepatotoxicity:** This is the hallmark of other first-line ATDs like Isoniazid, Rifampicin, and Pyrazinamide. Ethambutol is notably **non-hepatotoxic**, making it a safer choice in patients with pre-existing liver disease. * **Neurotoxicity:** While peripheral neuropathy can occur rarely, it is much more characteristic of Isoniazid (prevented by Pyridoxine). **Clinical Pearls for NEET-PG:** * **Hyperuricemia:** Ethambutol inhibits the excretion of uric acid, which can precipitate **acute gouty arthritis**. * **Monitoring:** Patients on Ethambutol should undergo baseline and monthly visual acuity and color vision (Ishihara chart) testing. * **Mnemonic:** Remember **"E"** for **E**thambutol and **"E"** for **E**ye (Optic neuritis).

Question 520: Which of the following statements about Fluconazole is most accurate?

A. It is effective in the treatment of Aspergillosis.
B. It does not penetrate the blood brain barrier.
C. Its oral bioavailability is less than that of ketoconazole.
D. It inhibits demethylation of lanosterol. (Correct Answer)

Explanation: **Explanation:** **1. Why the correct answer is right:** Fluconazole belongs to the **Azole** class of antifungals. Its primary mechanism of action is the inhibition of the fungal enzyme **14-alpha-demethylase** (a cytochrome P450 enzyme). This enzyme is responsible for the **demethylation of lanosterol**, converting it into ergosterol. Ergosterol is a vital component of the fungal cell membrane; its depletion leads to membrane instability and fungal cell death. **2. Why the other options are incorrect:** * **Option A:** Fluconazole has **no activity against *Aspergillus* species**. The drug of choice for invasive Aspergillosis is Voriconazole or Amphotericin B. * **Option B:** Fluconazole has **excellent CNS penetration** (reaching 80-90% of plasma levels). This makes it the drug of choice for maintenance therapy in Cryptococcal meningitis. * **Option C:** Fluconazole has very **high oral bioavailability (>90%)**, which is superior to Ketoconazole and Itraconazole. Unlike Ketoconazole, its absorption is not dependent on gastric acidity. **3. High-Yield Clinical Pearls for NEET-PG:** * **Spectrum:** Highly effective against *Candida albicans* and *Cryptococcus*, but *Candida krusei* and *Candida glabrata* are often resistant. * **Excretion:** It is the only azole primarily excreted **unchanged in the urine**, making it useful for fungal UTIs but requiring dose adjustment in renal failure. * **Side Effects:** It is the least hepatotoxic among the azoles but can cause QT prolongation. * **Teratogenicity:** It is generally avoided in pregnancy (Category C/D) due to the risk of fetal craniofacial abnormalities.

Practice by Chapter

Beta-Lactam Antibiotics

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Aminoglycosides

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Macrolides and Ketolides

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Tetracyclines

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Quinolones

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Sulfonamides and Trimethoprim

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Antimycobacterial Drugs

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Antifungal Agents

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Antiviral Drugs

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Antiparasitic Agents

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Principles of Antimicrobial Selection

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Antimicrobial Resistance

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