Antimicrobial Agents Practice Questions

Q: Which of the following is the major side effect of rifampicin?

Hepatotoxicity. **Explanation:** **Rifampicin** is a key bactericidal drug used in the treatment of Tuberculosis (TB) and Leprosy. Its mechanism of action involves the inhibition of DNA-dependent RNA polymerase [1]. **Why Hepatotoxicity is the correct answer:** Hepatotoxicity is the most significant and common major side effect of Rifampicin. It typically manifests as transient asymptomatic elevations in liver enzymes or, more seriously, as cholestatic jaundice. Rifampicin acts as a potent **microsomal enzyme inducer** (Cytochrome P450), which can increase the metabolism of other drugs and potentially enhance the hepatotoxic metabolites of co-administered drugs like Isoniazid (INH) and Pyrazinamide (PZA) [3]. **Analysis of Incorrect Options:** * **A. Renal failure:** While Rifampicin can rarely cause acute interstitial nephritis or acute tubular necrosis (often associated with intermittent therapy), it is not the *major* or most frequent side effect [2]. * **C & D. Bone marrow suppression/Blood dyscrasias:** These are rare adverse effects. While thrombocytopenia or leukopenia can occur (often as an immune-mediated "flu-like syndrome" during intermittent dosing), they are not the primary clinical concern compared to liver injury [2]. **High-Yield Clinical Pearls for NEET-PG:** * **Orange-red discoloration:** Rifampicin causes harmless orange-red coloring of urine, sweat, tears, and saliva—a classic "must-know" for patient counseling. * **Enzyme Induction:** It is a powerful inducer of CYP3A4, reducing the efficacy of oral contraceptives, warfarin, and antiretrovirals. * **Flu-like Syndrome:** Occurs mainly when the drug is taken irregularly or in high doses intermittently [2]. * **Mnemonic:** Remember the **4 R's** of Rifampicin: **R**NA polymerase inhibitor, **R**evs up microsomal enzymes, **R**ed-orange secretions, and **R**ash/Hepatotoxicity.

Q: Ototoxicity and nephrotoxicity are characteristic adverse effects of which drug class?

Aminoglycosides. **Aminoglycosides** (e.g., Gentamicin, Amikacin, Streptomycin) are the correct answer because they are notorious for their narrow therapeutic index, specifically causing **ototoxicity** and **nephrotoxicity** [2, 3].1. **Ototoxicity:** Aminoglycosides accumulate in the endolymph and perilymph of the inner ear, damaging sensory hair cells [1, 2]. This can manifest as **vestibular toxicity** (vertigo, ataxia) or **cochlear toxicity** (tinnitus, high-frequency hearing loss) [3]. This damage is often irreversible [1, 3].2. **Nephrotoxicity:** They are taken up by the proximal tubule cells in the kidney, leading to **Acute Tubular Necrosis (ATN)** [1]. This is usually reversible upon drug discontinuation [1, 3].**Analysis of Incorrect Options:** * **Chloramphenicol:** Primarily associated with **Bone Marrow Suppression** (dose-dependent) and **Aplastic Anemia** (idiosyncratic). In neonates, it causes **Gray Baby Syndrome** due to deficient glucuronidation. * **Fluoroquinolones:** Known for causing **tendon rupture** (Achilles tendon), cartilage damage in children, and QTc prolongation. * **β-Lactam antibiotics:** Generally safe; the most common adverse effects are **hypersensitivity reactions** (rashes to anaphylaxis) and, at high doses, seizures.**High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic:** "Aminoglycosides: **N**ephrotoxicity, **O**totoxicity, **T**eratogen, **N**euromuscular blockade" (**NOT N**). * **Risk Factors:** Concurrent use of **Loop Diuretics** (e.g., Furosemide) significantly potentiates the risk of ototoxicity. * **Monitoring:** Therapeutic Drug Monitoring (TDM) is essential to minimize toxicity. * **Neomycin** is the most nephrotoxic, while **Streptomycin** is the most vestibulotoxic.

Q: Peripheral neuritis due to isoniazid is caused by the formation of which complex?

Hydrazone complex. **Explanation:** The correct answer is **A. Hydrazone complex.** **Mechanism of Action:** Isoniazid (INH) is structurally similar to Pyridoxine (Vitamin B6). In the body, INH reacts with pyridoxal phosphate (the active form of B6) to form a **pyridoxal-isoniazid hydrazone complex**. This reaction leads to peripheral neuritis through two mechanisms: 1. It inhibits the enzyme **pyridoxine kinase**, preventing the conversion of pyridoxine to its active form. 2. It increases the renal excretion of pyridoxine. The resulting deficiency of Vitamin B6 impairs the synthesis of neurotransmitters (like GABA), leading to nerve damage. **Analysis of Incorrect Options:** * **B. Isobutane complex:** This is a chemical hydrocarbon and has no relevance to isoniazid metabolism or pharmacology. * **C. Isoazoic complex:** This is a distractor term; while "azo" compounds exist in chemistry, they are not involved in the pathogenesis of INH-induced neuropathy. * **D. Hydralazine complex:** Hydralazine is an antihypertensive drug that can also cause B6 deficiency and peripheral neuritis, but it does not form a complex *with* isoniazid; rather, it is a separate drug with a similar side-effect profile. **High-Yield Clinical Pearls for NEET-PG:** * **Prophylaxis:** Peripheral neuritis can be prevented by co-administering **Pyridoxine (10–50 mg/day)**. * **Risk Factors:** It is more common in **slow acetylators** (due to higher drug levels), malnourished individuals, chronic alcoholics, and diabetics. * **Other Side Effects:** Hepatotoxicity (most common), Sideroblastic anemia, and Drug-induced Lupus (DILE). * **Metabolism:** INH is metabolized via **Acetylation** (Phase II reaction) by the enzyme NAT2.

Q: Chemoprophylaxis with tetracycline is useful in which of the following conditions?

Cholera. **Explanation:** **1. Why Cholera is the Correct Answer:** Tetracyclines (specifically **Doxycycline**) are the drugs of choice for the chemoprophylaxis of **Cholera** in household contacts and during epidemics. While rehydration is the mainstay of treatment, Doxycycline reduces the bacterial load, shortens the duration of diarrhea, and limits the shedding of *Vibrio cholerae* in stools, thereby breaking the chain of transmission. A single dose of 300 mg Doxycycline is typically sufficient for prophylaxis in adults. **2. Why the Other Options are Incorrect:** * **Brucellosis:** Tetracyclines (Doxycycline) are used for the **treatment** of Brucellosis (usually in combination with Rifampicin or Streptomycin), but they are not standard for routine chemoprophylaxis. * **Meningitis:** The drug of choice for chemoprophylaxis against *Neisseria meningitidis* is **Rifampicin**. Ciprofloxacin or Ceftriaxone are also used. Tetracyclines do not achieve adequate CSF penetration for this purpose. * **Leptospirosis:** While Doxycycline is used for the prophylaxis of Leptospirosis (200 mg once weekly), the question asks for the most established use in a classic "single-drug" context. In the hierarchy of NEET-PG questions, Tetracycline/Doxycycline is most classically associated with **Cholera** prophylaxis. **3. Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Doxycycline is the DOC for Rickettsial infections, Chlamydia, Brucellosis (combined), and Cholera. * **Contraindications:** Avoid in pregnancy and children <8 years due to **chelation of Calcium**, leading to teeth discoloration and bone growth retardation. * **Adverse Effect:** Phototoxicity (most common with Demeclocycline and Doxycycline) and Fanconi syndrome (with outdated tetracyclines). * **Prophylaxis Summary:** * Meningococcal Meningitis: Rifampicin. * Rheumatic Fever: Benzathine Penicillin G. * Pertussis: Erythromycin.

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].

Question 1

Which of the following is the major side effect of rifampicin?

Accepted Answer

Hepatotoxicity

Answer

Renal failure

Answer

Bone marrow suppression

Answer

Blood dyscrasias

Question 2

Ototoxicity and nephrotoxicity are characteristic adverse effects of which drug class?

Accepted Answer

Aminoglycosides

Answer

Chloramphenicol

Answer

Fluoroquinolones

Answer

b-Lactam antibiotics

Question 3

Peripheral neuritis due to isoniazid is caused by the formation of which complex?

Accepted Answer

Hydrazone complex

Answer

Isobutane complex

Answer

Isoazoic complex

Answer

Hydralazine complex

Question 4

Chemoprophylaxis with tetracycline is useful in which of the following conditions?

Accepted Answer

Cholera

Answer

Brucellosis

Answer

Meningitis

Answer

Leptospirosis

Question 5

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 6

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

Accepted Answer

Aesunate

Answer

Doxycycline

Answer

Chloroquine

Answer

Mefloquine

Question 7

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 8

Side effects of isoniazid are all EXCEPT?

Accepted Answer

Thrombocytopenia

Answer

Hepatitis

Answer

Optic neuritis

Answer

Peripheral Neuropathy

Question 9

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

Accepted Answer

Quinolone

Answer

Penicillin G

Answer

Cephalosporin

Answer

Erythromycin

Question 10

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

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

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