Antimicrobial Agents Practice Questions

Q: Which of the following statements about penicillin G is TRUE?

It can be used for rat bite fever.. **Explanation:** **Penicillin G (Benzylpenicillin)** remains a cornerstone of therapy for specific infections despite its narrow spectrum. 1. **Why Option C is Correct:** Rat-bite fever, caused by *Streptobacillus moniliformis* or *Spirillum minus*, is highly sensitive to penicillin. Penicillin G is the **drug of choice** for this condition. It is also the gold standard for syphilis (*Treponema pallidum*), gas gangrene (*Clostridium perfringens*), and anthrax [1]. 2. **Why Other Options are Incorrect:** * **Option A:** Penicillin G is **acid-labile** and is destroyed by gastric acid [2]. Therefore, it cannot be administered orally and must be given parenterally (IV/IM). Penicillin V (Phenoxymethylpenicillin) is the acid-stable oral alternative [2]. * **Option B:** It has a **narrow spectrum**, primarily targeting Gram-positive cocci (Streptococci), Gram-positive bacilli, and some Gram-negative cocci (Meningococci) [1]. It is ineffective against most Gram-negative bacilli due to their outer membrane barrier. * **Option D:** Probenecid **increases** the duration of action. It competes with penicillin for the organic anion transporter (OAT) in the renal tubules, inhibiting its active tubular secretion and thereby raising its plasma concentration and half-life [3]. **High-Yield Clinical Pearls for NEET-PG:** * **Jarisch-Herxheimer Reaction:** A classic adverse effect seen when treating syphilis with Penicillin G due to the release of endotoxins from dying spirochetes. * **Repository Forms:** Procaine and Benzathine penicillin are long-acting IM formulations used for prophylaxis of rheumatic fever and treatment of syphilis. * **Excretion:** 90% is via tubular secretion; only 10% is via glomerular filtration [3].

Q: Which of the following drugs is NOT used for malaria prophylaxis?

Aesunate. **Explanation:** The core concept here is the distinction between **chemoprophylaxis** (prevention) and **chemotherapy** (treatment) of malaria. **Why Artesunate is the correct answer:** Artesunate is a water-soluble Artemisinin derivative. It is the drug of choice for the **treatment** of severe and complicated malaria (P. falciparum) due to its rapid action on the erythrocytic stages of the parasite. However, it is **never used for prophylaxis** because of its very short half-life (approx. 30–60 minutes), which would require multiple daily doses, and to prevent the development of drug resistance to this life-saving class of antimalarials. **Analysis of Incorrect Options:** * **Chloroquine (Option C):** Historically the gold standard for prophylaxis. It is still used for prophylaxis in areas with chloroquine-sensitive malaria (e.g., parts of Central America). * **Mefloquine (Option D):** Used for long-term prophylaxis in areas with chloroquine resistance. It is taken once weekly, starting 2 weeks before travel. * **Doxycycline (Option A):** Used for short-term prophylaxis, especially in areas with multi-drug resistant P. falciparum. It is taken daily. **High-Yield NEET-PG Pearls:** 1. **Prophylaxis Choice:** Depends on the duration of stay. **Short-term** ( 6 weeks): Mefloquine. 2. **Contraindications:** Mefloquine is contraindicated in patients with neuropsychiatric disorders or seizures. Doxycycline is contraindicated in pregnancy and children <8 years. 3. **Pregnancy:** Chloroquine is safe for prophylaxis in all trimesters. 4. **Primaquine:** Used for "Terminal Prophylaxis" to prevent relapses of P. vivax and P. ovale by targeting hypnozoites. Always check G6PD status before administration.

Q: Bull's eye maculopathy is an adverse effect caused by which of the following medications?

Chloroquine. **Explanation:** **Bull’s eye maculopathy** is a classic, high-yield ocular side effect primarily associated with the long-term use of **Chloroquine (CQ)** and its derivative, **Hydroxychloroquine (HCQ)**. **Why Chloroquine is correct:** Chloroquine has a high affinity for melanin-containing tissues, leading to its accumulation in the **Retinal Pigment Epithelium (RPE)**. It inhibits lysosomal enzymes within the RPE, causing metabolic stress and subsequent degeneration of the photoreceptors. Clinically, this manifests as a central island of spared RPE surrounded by a ring of depigmentation (atrophy), which is further encircled by a ring of normal pigmentation—resembling a **"Bull’s Eye."** On Fundus Fluorescein Angiography (FFA), this appears as a "window defect." **Why the other options are incorrect:** * **Lumefantrine:** Used in combination therapy for malaria (ACT), it does not have significant documented retinal toxicity. * **Quinine:** While toxic to the eye, Quinine causes **"Quinine Amblyopia,"** characterized by sudden vision loss, profound retinal arteriolar narrowing (vasospasm), and optic atrophy, rather than a bull’s eye pattern. * **Primaquine:** Primarily associated with systemic side effects like hemolysis in G6PD-deficient patients; it does not cause maculopathy. **NEET-PG High-Yield Pearls:** 1. **Screening:** The most sensitive early tests for HCQ/CQ toxicity are **Automated Visual Fields (10-2)** and **Spectral Domain OCT** (showing the "Flying Saucer" sign). 2. **Dosage:** Toxicity risk increases significantly when the daily dose of HCQ exceeds **5 mg/kg** of real body weight. 3. **Irreversibility:** Once Bull’s eye maculopathy is visible on fundoscopy, the damage is usually **permanent and may progress** even after stopping the drug (washout effect). 4. **Other causes of Bull's Eye Maculopathy:** Stargardt’s disease, Cone-Dystrophy, and Batten’s disease.

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 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: 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].

Q: Which of the following anti-HIV drugs should never be given as rechallenge once a history of producing an allergic reaction with the drug is known?

Abacavir. **Explanation:** The correct answer is **Abacavir (Option B)**. Abacavir is associated with a severe, potentially life-threatening **Hypersensitivity Reaction (HSR)** in approximately 5–8% of patients. [1] This reaction is strongly linked to the presence of the **HLA-B*5701 allele**. [1] If a patient develops an allergic reaction to Abacavir, **rechallenge is strictly contraindicated** because it can trigger a rapid, more severe, and fatal systemic reaction (anaphylaxis or multi-organ failure) within hours. **Why the other options are incorrect:** * **Lamivudine (3TC) & Zidovudine (AZT):** These are Nucleoside Reverse Transcriptase Inhibitors (NRTIs). [2] While they have side effects (e.g., AZT causes bone marrow suppression and macrocytic anemia), they are not typically associated with the specific, fatal rechallenge-induced hypersensitivity seen with Abacavir. * **Nelfinavir:** This is a Protease Inhibitor (PI). Its primary side effect is diarrhea. While any drug can cause an allergy, it does not carry the "never rechallenge" black box warning associated with Abacavir’s genetic predisposition. **High-Yield Clinical Pearls for NEET-PG:** * **Mandatory Screening:** Always screen for **HLA-B*5701** before initiating Abacavir. [1] If positive, the drug should never be used. * **Clinical Presentation:** Abacavir HSR typically presents within the first 6 weeks of treatment with fever, rash, GI symptoms, and respiratory distress. * **Nevirapine (NNRTI):** Another anti-HIV drug known for severe skin reactions (Stevens-Johnson Syndrome), but the specific "rechallenge contraindication" based on HLA-linkage is most classically tested with Abacavir. * **Mnemonic:** "A-B-C" — **A**bacavir, **B**ad reaction, **C**ontraindicated to rechallenge.

Q: Which of the following binds to viral envelope glycoprotein preventing the conformational changes required for the fusion of viral and cellular membranes?

Enfuvirtide. **Explanation:** **Correct Option: C. Enfuvirtide** Enfuvirtide is a unique antiretroviral agent classified as a **Fusion Inhibitor**. Its mechanism of action involves binding to the **gp41** subunit of the viral envelope glycoprotein. By binding to this subunit, it prevents the necessary conformational changes required for the fusion of the HIV-1 envelope with the host cell membrane (CD4+ T-cell). Since the virus cannot fuse, it cannot enter the host cell. **Analysis of Incorrect Options:** * **A. Abacavir:** This is a Nucleoside Reverse Transcriptase Inhibitor (**NRTI**). It acts by inhibiting the viral reverse transcriptase enzyme, leading to DNA chain termination. It does not affect viral entry. * **B. Indinavir:** This is a **Protease Inhibitor (PI)**. It prevents the cleavage of the Gag-Pol polyprotein precursor, resulting in the production of immature, non-infectious virions. * **D. Oseltamivir:** This is a **Neuraminidase Inhibitor** used for Influenza A and B. It prevents the release of new virions from infected cells; it is not used for HIV. **High-Yield NEET-PG Pearls:** * **Route of Administration:** Enfuvirtide is the only antiretroviral administered **subcutaneously** (twice daily). * **Site of Action:** It targets **gp41**, whereas Maraviroc (another entry inhibitor) targets the host cell **CCR5 receptor**. * **Resistance:** Resistance to Enfuvirtide occurs via mutations in the *env* gene. * **Side Effects:** Local injection site reactions (nodules, erythema) are seen in almost 100% of patients.

Question 1

Which of the following statements about penicillin G is TRUE?

Accepted Answer

It can be used for rat bite fever.

Answer

It is administered orally.

Answer

It has a wide spectrum of activity.

Answer

Co-administration of probenecid decreases its duration of action.

Question 2

Which of the following drugs is NOT used for malaria prophylaxis?

Accepted Answer

Aesunate

Answer

Doxycycline

Answer

Chloroquine

Answer

Mefloquine

Question 3

Bull's eye maculopathy is an adverse effect caused by which of the following medications?

Accepted Answer

Chloroquine

Answer

Lumefantrine

Answer

Quinine

Answer

Primaquine

Question 4

Side effects of isoniazid are all EXCEPT?

Accepted Answer

Thrombocytopenia

Answer

Hepatitis

Answer

Optic neuritis

Answer

Peripheral Neuropathy

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

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 8

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

Accepted Answer

Chloramphenicol

Answer

Penicillin

Answer

Rifampicin

Answer

Erythromycin

Question 9

Which of the following anti-HIV drugs should never be given as rechallenge once a history of producing an allergic reaction with the drug is known?

Accepted Answer

Abacavir

Answer

Lamivudine

Answer

Zidovudine

Answer

Nelfinavir

Question 10

Which of the following binds to viral envelope glycoprotein preventing the conformational changes required for the fusion of viral and cellular membranes?

Accepted Answer

Enfuvirtide

Answer

Abacavir

Answer

Indinavir

Answer

Oseltamivir

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

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