Antimicrobial Agents Practice Questions

Q: Which of the following statements are true regarding cefepime?

It is a fourth-generation cephalosporin. **Explanation:** **Cefepime** is a parenteral **fourth-generation cephalosporin** [1]. It is characterized by its "zwitterionic" structure, which allows it to penetrate the outer membrane of Gram-negative bacteria rapidly and provides high resistance to many beta-lactamases. * **Why Option A is correct:** Cefepime (along with Cefpirome) belongs to the 4th generation [1]. These agents have an extended spectrum, combining the strong Gram-positive activity of the 1st generation with the potent Gram-negative activity of the 3rd generation. * **Why Option B is incorrect:** Cefepime has a half-life of approximately 2 hours. It requires **twice-daily (q12h)** or thrice-daily (q8h) dosing for serious infections; it is not a once-a-day drug (unlike Ceftriaxone). * **Why Option C is incorrect (Contextual):** While Cefepime **does** possess excellent antipseudomonal action [1], the question asks for the most defining characteristic or the "best" true statement in a single-choice format. In many standard pharmacological classifications, its generation is its primary identifier. *(Note: In some exam patterns, this could be a multiple-correct question, but as a single choice, its classification is the definitive answer).* * **Why Option D is incorrect:** Cefepime is primarily excreted unchanged by the kidneys. Therefore, **dose adjustment is mandatory** in patients with renal impairment to prevent neurotoxicity (e.g., encephalopathy, seizures). **High-Yield Clinical Pearls for NEET-PG:** * **Spectrum:** Highly active against *Pseudomonas aeruginosa* and Enterobacteriaceae producing AmpC beta-lactamases [1]. * **Neurotoxicity:** A unique side effect of Cefepime, especially in elderly or renal-impaired patients, is non-convulsive status epilepticus. * **Comparison:** Unlike 3rd generation drugs, 4th generation cephalosporins are poor inducers of chromosomal beta-lactamases.

Q: Side effects of isoniazid are all EXCEPT?

Thrombocytopenia. **Explanation:** Isoniazid (INH) is a cornerstone of anti-tubercular therapy (ATT), but it is associated with specific adverse drug reactions (ADRs) that are frequently tested in NEET-PG. **Why Thrombocytopenia is the correct answer:** Thrombocytopenia is **not** a characteristic side effect of Isoniazid. While many drugs can cause bone marrow suppression, thrombocytopenia is classically associated with **Rifampicin** (via immune-mediated mechanisms) or Ethambutol (rarely), rather than INH. **Analysis of incorrect options:** * **Hepatitis (Option A):** This is the most common major toxic effect of INH. It is caused by the metabolite **acetylhydrazine**. The risk increases with age, alcohol consumption, and pre-existing liver disease. * **Optic Neuritis (Option B):** While more classically associated with Ethambutol, INH can also cause optic neuritis (though less frequently). In the context of "all except" questions, it is considered a recognized side effect of INH. * **Peripheral Neuropathy (Option C):** This is a hallmark side effect caused by **pyridoxine (Vitamin B6) deficiency**. INH competes with pyridoxal phosphate and increases its excretion. It is more common in "slow acetylators." **High-Yield Clinical Pearls for NEET-PG:** 1. **Mechanism of Action:** Inhibits mycolic acid synthesis by targeting the *inhA* gene. 2. **Metabolism:** Metabolized by **Acetylation** (Phase II reaction). Slow acetylators are prone to neuropathy; fast acetylators may be prone to hepatotoxicity. 3. **Prophylaxis:** Peripheral neuropathy can be prevented by co-administering **Pyridoxine (10–25 mg/day)**. 4. **Sideroblastic Anemia:** INH can also cause microcytic hypochromic anemia due to interference with heme synthesis (B6 deficiency). 5. **Drug-Induced Lupus:** INH is a well-known cause of Systemic Lupus Erythematosus (SLE), usually associated with anti-histone antibodies.

Q: Which of the following agents is a fusion inhibitor?

Enfuvirtide. **Explanation:** **Correct Answer: B. Enfuvirtide** Enfuvirtide is the prototype **fusion inhibitor**. Its mechanism of action involves binding to the **gp41** subunit of the viral envelope glycoprotein. This prevents the conformational change required for the fusion of the HIV viral envelope with the host cell (CD4+ T-cell) membrane, thereby blocking viral entry. It is administered subcutaneously and is typically reserved for treatment-experienced patients with multidrug-resistant HIV. **Analysis of Incorrect Options:** * **A. Zidovudine (AZT):** This is a **Nucleoside Reverse Transcriptase Inhibitor (NRTI)**. It acts as a thymidine analogue that causes premature chain termination during the synthesis of viral DNA by reverse transcriptase. * **C. Nevirapine:** This is a **Non-Nucleoside Reverse Transcriptase Inhibitor (NNRTI)**. It binds directly to the reverse transcriptase enzyme at a site distinct from the active site (allosteric site), inducing a conformational change that inactivates the enzyme. * **D. Ritonavir:** This is a **Protease Inhibitor (PI)**. It inhibits the viral protease enzyme (HIV-1 protease), preventing the cleavage of gag-pol polyproteins into mature, functional proteins, resulting in the production of immature, non-infectious virions. **High-Yield Clinical Pearls for NEET-PG:** * **Maraviroc** is another entry inhibitor, but it is a **CCR5 antagonist** (blocks the host cell co-receptor), whereas Enfuvirtide blocks the viral protein gp41. * **Ritonavir** is rarely used for its own antiviral effect today; it is primarily used as a **"pharmacokinetic booster"** because it is a potent inhibitor of CYP3A4, increasing the plasma levels of other protease inhibitors (e.g., Lopinavir). * **Zidovudine** is the drug of choice for preventing vertical transmission (mother-to-child) of HIV during pregnancy and labor.

Q: Which of the following antimicrobial agents is not given in pregnancy?

Quinolone. **Explanation:** The correct answer is **Quinolones (e.g., Ciprofloxacin, Levofloxacin)**. **1. Why Quinolones are contraindicated:** Quinolones are generally avoided during pregnancy because they have a high affinity for bone and cartilage. Experimental animal studies have shown that these agents can cause **arthropathy** and permanent damage to the **weight-bearing joints** (cartilage erosion) in developing fetuses. They are classified as FDA Pregnancy Category C. **2. Analysis of Incorrect Options:** * **Penicillin G (Option A):** Penicillins are considered the safest antibiotics during pregnancy (Category B). They do not have teratogenic effects and are the drug of choice for conditions like syphilis in pregnant women. * **Cephalosporins (Option C):** Like penicillins, cephalosporins (e.g., Ceftriaxone, Cephalexin) are Category B drugs. They are widely used and considered safe for treating urinary tract infections and respiratory infections in pregnancy. * **Erythromycin (Option D):** Erythromycin (base/stearate) is considered safe (Category B). However, the **Estolate salt** of erythromycin is contraindicated as it may cause cholestatic hepatitis in the mother. **3. NEET-PG High-Yield Pearls (Mnemonic: SAFE / FAST):** * **SAFE Antibiotics in Pregnancy:** **S**ulfonamides (only in mid-trimester), **A**mpicillin/Penicillins, **F**irst-line Cephalosporins, **E**rythromycin. * **Antibiotics to AVOID (Mnemonic: MCAT):** * **M**etronidazole (avoid in 1st trimester). * **C**hloramphenicol (Gray Baby Syndrome). * **A**minoglycosides (Ototoxicity/CN VIII damage). * **T**etracyclines (Discolored teeth and bone growth inhibition). * **Nitrofurantoin:** Safe until 36 weeks; avoid at term due to risk of neonatal hemolysis (G6PD deficiency).

Q: Which of the following statements about Acyclovir is false?

Doesn't work on other viruses. ### Explanation **Correct Option: C (Doesn't work on other viruses)** This statement is **false** (making it the correct answer for this question). While Acyclovir is most potent against Herpes Simplex Virus (HSV-1 and HSV-2) and Varicella-Zoster Virus (VZV), it also possesses activity against other members of the Herpesviridae family, such as **Epstein-Barr Virus (EBV)** and **Cytomegalovirus (CMV)**, though its clinical efficacy against CMV is limited compared to Ganciclovir. **Analysis of Other Options:** * **Option A (Useful for recurrent infections):** This is a true statement. Acyclovir is highly effective in reducing the duration and severity of both primary and recurrent genital and oral herpes. * **Option B (Inhibits thymidine kinase):** This is a true statement regarding its mechanism. Acyclovir is a prodrug that must be phosphorylated to Acyclovir-monophosphate by **viral Thymidine Kinase** [1], [2]. It then competes with deoxyguanosine triphosphate to inhibit **viral DNA polymerase**, leading to DNA chain termination [1]. * **Option D (Metabolized and excreted through kidneys):** This is true. Acyclovir is primarily excreted unchanged via glomerular filtration and tubular secretion [1], [3]. Dosage adjustment is mandatory in patients with renal impairment to prevent neurotoxicity and crystalline nephropathy. **High-Yield NEET-PG Pearls:** * **Mechanism of Resistance:** Most common cause is the absence or mutation of viral **Thymidine Kinase** [2]. * **Drug of Choice:** For HSV encephalitis, Neonatal HSV, and Herpes Zoster (Shingles). * **Adverse Effect:** Reversible **crystalline nephropathy** (prevented by adequate hydration) and neurotoxicity (tremors, seizures). * **Valacyclovir:** A prodrug of acyclovir with much higher oral bioavailability (the "L-valyl ester" of acyclovir) [3].

Q: In cotrimoxazole, what is the ratio of sulphamethoxazole to trimethoprim?

5:1. ### Explanation **Correct Answer: C. 5:1** **1. Underlying Medical Concept:** Cotrimoxazole is a fixed-dose combination of **Sulphamethoxazole (SMZ)** and **Trimethoprim (TMP)**. These two drugs act synergistically by blocking sequential steps in bacterial folic acid synthesis (Sequential Blockade). * **The Ratio in the Tablet:** The drugs are combined in a **5:1 ratio** (e.g., 400 mg SMZ + 80 mg TMP). * **The Ratio in the Plasma:** Because Trimethoprim has a significantly larger volume of distribution and better lipid solubility than Sulphamethoxazole, it distributes more widely into tissues. To achieve the optimal synergistic therapeutic concentration in the **plasma (which is 20:1)**, they must be administered in a **5:1 dose ratio**. **2. Analysis of Incorrect Options:** * **Option A (2:1) & B (1:1):** These ratios do not provide the necessary pharmacokinetic balance required to reach the 20:1 steady-state plasma concentration needed for maximal antibacterial activity. * **Option D (1:5):** This reverses the components. Sulphamethoxazole must be the higher dose component because it has a smaller volume of distribution and lower potency per milligram compared to Trimethoprim. **3. NEET-PG High-Yield Clinical Pearls:** * **Mechanism:** SMZ inhibits *Dihydropteroate synthase*; TMP inhibits *Dihydrofolate reductase*. * **Spectrum:** It is the drug of choice for *Pneumocystis jirovecii* pneumonia, *Nocardia*, and *Stenotrophomonas maltophilia*. * **Adverse Effects:** Watch for **megaloblastic anemia** (due to folate deficiency) and **Stevens-Johnson Syndrome** (due to the sulfonamide component). * **Resistance:** Bacteria usually develop resistance by acquiring plasmids that code for altered dihydrofolate reductase enzymes.

Q: Gray baby syndrome is caused by which of the following drugs?

Chloramphenicol. **Explanation:** **Gray Baby Syndrome** is a serious and potentially fatal adverse reaction associated with the administration of **Chloramphenicol** in neonates, particularly premature infants [2]. **Mechanism of Action:** The syndrome occurs due to the neonate's physiological immaturity in two key areas: 1. **Glucuronosyltransferase Deficiency:** Neonates lack sufficient levels of this hepatic enzyme, which is required to metabolize chloramphenicol via glucuronidation [1]. 2. **Inadequate Renal Excretion:** Immature kidneys cannot effectively excrete the unconjugated drug [2]. This leads to the accumulation of toxic levels of chloramphenicol, which inhibits mitochondrial protein synthesis, resulting in myocardial depression, vascular collapse, and the characteristic "ashen gray" cyanosis. **Analysis of Incorrect Options:** * **A. Penicillin:** Primarily associated with hypersensitivity reactions (Type I IgE-mediated) and seizures at very high doses. * **C. Rifampicin:** Known for causing orange-colored secretions (urine, sweat, tears) and hepatotoxicity. * **D. Erythromycin:** Commonly associated with GI upset and, in neonates, an increased risk of Infantile Hypertrophic Pyloric Stenosis (IHPS). **NEET-PG High-Yield Pearls:** * **Clinical Presentation:** Abdominal distension, vomiting, progressive pallid cyanosis (gray color), and circulatory collapse. * **Other Chloramphenicol Side Effects:** Dose-dependent bone marrow suppression (reversible) and **Aplastic Anemia** (idiosyncratic, irreversible, and most dreaded). * **Drug of Choice:** Chloramphenicol remains a backup for enteric fever (Typhoid) [1] and bacterial meningitis in patients with severe penicillin allergy [2].

Question 1

Which of the following statements are true regarding cefepime?

Accepted Answer

It is a fourth-generation cephalosporin

Answer

Once a day dose is sufficient

Answer

It possesses antipseudomonal action

Answer

Its dose should not be reduced in renal pathology

Question 2

What is the drug of choice for bacterial vaginosis in a pregnant female?

Accepted Answer

Metronidazole

Answer

Clindamycin

Answer

Erythromycin

Answer

Fluconazole

Question 3

Side effects of isoniazid are all EXCEPT?

Accepted Answer

Thrombocytopenia

Answer

Hepatitis

Answer

Optic neuritis

Answer

Peripheral Neuropathy

Question 4

Which of the following agents is a fusion inhibitor?

Accepted Answer

Enfuvirtide

Answer

Zidovudine

Answer

Nevirapine

Answer

Ritonavir

Question 5

Which of the following antimicrobial agents is not given in pregnancy?

Accepted Answer

Quinolone

Answer

Penicillin G

Answer

Cephalosporin

Answer

Erythromycin

Question 6

Which of the following statements about Acyclovir is false?

Accepted Answer

Doesn't work on other viruses

Answer

Useful and efficient only for recurrent herpes infections

Answer

Inhibits thymidine kinase

Answer

Metabolized and excreted through kidneys

Question 7

In cotrimoxazole, what is the ratio of sulphamethoxazole to trimethoprim?

Accepted Answer

5:1

Answer

2:1

Answer

1:1

Answer

1:5

Question 8

All of the following are true about the therapy for tuberculosis, except?

Accepted Answer

A 'flu-like syndrome' is usually seen in people taking rifampicin on a daily basis.

Answer

Ethambutol accumulates in renal failure.

Answer

Hyperuricemia is a recognized side effect of pyrazinamide.

Answer

Red-green color impairment is an early sign of ethambutol-induced optic neuritis.

Question 9

Gray baby syndrome is caused by which of the following drugs?

Accepted Answer

Chloramphenicol

Answer

Penicillin

Answer

Rifampicin

Answer

Erythromycin

Question 10

Select the antibiotic most frequently associated with Gray baby syndrome?

Accepted Answer

Chloramphenicol

Answer

Tetracycline

Answer

Streptomycin

Answer

Nitrofurantoin

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

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