Neomycin – chemistry and use MCQs With Answer

Neomycin – chemistry and use MCQs With Answer

Neomycin is an aminoglycoside antibiotic composed of multiple amino‑sugar residues linked to an aminocyclitol core. Its polar, polycationic chemistry determines poor oral absorption but high topical and gastrointestinal activity. Neomycin acts on the bacterial 30S ribosomal subunit causing misreading of mRNA and bactericidal effects against aerobic gram‑negative bacilli; resistance arises from modifying enzymes and 16S rRNA methylation. Clinically it’s used topically, for gut decontamination and hepatic encephalopathy, but systemic use is limited by nephrotoxicity and ototoxicity. Key pharmacy topics include formulation, stability, assay (HPLC), incompatibilities, dosing and therapeutic monitoring. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What chemical class does neomycin belong to?

• Aminoglycoside antibiotic
• Macrolide antibiotic
• Beta‑lactam antibiotic
• Tetracycline antibiotic

Correct Answer: Aminoglycoside antibiotic

Q2. What is the primary mechanism of action of neomycin?

• Inhibits bacterial DNA gyrase
• Blocks peptidoglycan cross‑linking
• Binds 30S ribosomal subunit causing mRNA misreading and inhibited initiation
• Inhibits folate synthesis by targeting dihydropteroate synthase

Correct Answer: Binds 30S ribosomal subunit causing mRNA misreading and inhibited initiation

Q3. Why is neomycin primarily used topically or orally for gut decontamination?

• Because it has excellent systemic bioavailability
• Because it is heat labile and only stable topically
• Because it has poor oral absorption but high local gastrointestinal activity
• Because it causes less toxicity when given intravenously

Correct Answer: Because it has poor oral absorption but high local gastrointestinal activity

Q4. Which two major toxicities limit systemic use of neomycin?

• Hepatotoxicity and agranulocytosis
• Cardiotoxicity and pulmonary fibrosis
• Nephrotoxicity and ototoxicity
• Pancreatitis and photosensitivity

Correct Answer: Nephrotoxicity and ototoxicity

Q5. The most common enzymatic resistance mechanisms to neomycin involve:

• Altered porin channels preventing entry
• Target site mutation in 50S ribosomal subunit
• Aminoglycoside‑modifying enzymes that acetylate, phosphorylate or adenylate the drug
• Efflux pumps specific for macrolides

Correct Answer: Aminoglycoside‑modifying enzymes that acetylate, phosphorylate or adenylate the drug

Q6. Neomycin’s antibacterial spectrum is best described as:

• Primarily anaerobic gram‑positive cocci
• Primarily aerobic gram‑negative bacilli with some gram‑positive synergy
• Broad activity against fungi and viruses
• Exclusive activity against Mycobacterium tuberculosis

Correct Answer: Primarily aerobic gram‑negative bacilli with some gram‑positive synergy

Q7. One approved non‑infectious use of oral neomycin is:

• Treatment of peptic ulcer disease
• Reduction of ammonia‑producing gut flora in hepatic encephalopathy
• Management of chronic obstructive pulmonary disease
• Systemic fungal suppression

Correct Answer: Reduction of ammonia‑producing gut flora in hepatic encephalopathy

Q8. Which statement about parenteral use of neomycin is correct?

• Neomycin is commonly given intravenously for sepsis
• Neomycin is given intramuscularly as first‑line therapy for pneumonia
• Neomycin is not used parenterally because of high systemic toxicity
• Neomycin is the preferred aminoglycoside for IV therapy

Correct Answer: Neomycin is not used parenterally because of high systemic toxicity

Q9. Which chemical property best describes neomycin molecules?

• Lipophilic and neutral
• Polycationic, highly polar and water‑soluble
• Strongly acidic and fat soluble
• Highly volatile and hydrophobic

Correct Answer: Polycationic, highly polar and water‑soluble

Q10. Uptake of neomycin into susceptible bacteria is enhanced by:

• Anaerobic metabolic pathways
• Oxygen‑dependent active transport across the cell membrane
• Passive diffusion through lipid bilayers
• Binding to bacterial DNA gyrase

Correct Answer: Oxygen‑dependent active transport across the cell membrane

Q11. High‑level aminoglycoside resistance due to methylation typically targets which molecule?

• Bacterial DNA polymerase
• 50S ribosomal RNA
• 16S rRNA of the 30S ribosomal subunit
• Peptidoglycan biosynthetic enzymes

Correct Answer: 16S rRNA of the 30S ribosomal subunit

Q12. A common analytical method for quantifying neomycin in formulations is:

• Gas chromatography with flame ionization detection
• High‑performance liquid chromatography (HPLC)
• Nuclear magnetic resonance imaging
• Thin layer chromatography using nonpolar solvent

Correct Answer: High‑performance liquid chromatography (HPLC)

Q13. Ototoxicity from neomycin is primarily due to damage of:

• Hepatocytes in the liver
• Cochlear and vestibular hair cells in the inner ear
• Alveolar macrophages in the lung
• Pancreatic beta cells

Correct Answer: Cochlear and vestibular hair cells in the inner ear

Q14. The structural backbone of neomycin includes:

• A polyketide macrolactone ring
• Multiple amino‑sugar residues linked to an aminocyclitol core
• A tetracyclic steroid nucleus
• A sulfonamide moiety attached to a benzene ring

Correct Answer: Multiple amino‑sugar residues linked to an aminocyclitol core

Q15. At physiological pH neomycin exists mainly as:

• A neutral zwitterion
• A polycation due to protonated amino groups
• A dianion from deprotonated carboxyl groups
• A lipophilic uncharged molecule

Correct Answer: A polycation due to protonated amino groups

Q16. Which monitoring is most useful to detect early nephrotoxicity from systemic aminoglycosides?

• Serum transaminases and bilirubin
• Serum creatinine and urine output
• Fasting blood glucose
• Serum amylase and lipase

Correct Answer: Serum creatinine and urine output

Q17. Concurrent use of which antibiotic class may antagonize the effect of neomycin?

• Beta‑lactams (synergistic with aminoglycosides)
• Glycopeptides (additive bactericidal action)
• Bacteriostatic agents like tetracyclines and chloramphenicol
• Fluoroquinolones (always potentiates activity)

Correct Answer: Bacteriostatic agents like tetracyclines and chloramphenicol

Q18. Commercial neomycin preparations are typically a mixture of:

• Neomycin B and neomycin C components
• Neomycin and gentamicin in fixed ratio
• Pure neomycin A only
• Neomycin combined with vancomycin

Correct Answer: Neomycin B and neomycin C components

Q19. Which enzyme families are involved in aminoglycoside inactivation?

• Acyltransferases, proteases and lipases
• Acetyltransferases, phosphotransferases and nucleotidyltransferases
• Glycosylases and oxidases only
• Methyltransferases that target 23S rRNA

Correct Answer: Acetyltransferases, phosphotransferases and nucleotidyltransferases

Q20. Neomycin is commonly combined in topical products with:

• Polymyxin and bacitracin for broad topical coverage
• Oral hypoglycemics for transdermal delivery
• Systemic anticoagulants to improve penetration
• Systemic antifungals for viral infections

Correct Answer: Polymyxin and bacitracin for broad topical coverage

Q21. Patients at increased risk of neomycin toxicity include those with:

• Acute hepatic failure only
• Renal impairment and concurrent loop diuretic therapy
• History of gastric ulcers
• Prior hypersensitivity to penicillins (no renal risk)

Correct Answer: Renal impairment and concurrent loop diuretic therapy

Q22. Regarding absorption from intact skin or intact gastrointestinal mucosa, neomycin is:

• Well absorbed and achieves high plasma levels
• Poorly absorbed from intact skin and GI tract
• Rapidly absorbed through intact skin but not GI tract
• Absorbed only when combined with beta‑lactams

Correct Answer: Poorly absorbed from intact skin and GI tract

Q23. For systemic aminoglycoside therapy (not typical for neomycin), therapeutic drug monitoring focuses on:

• Peak and trough plasma concentrations to minimize toxicity and ensure efficacy
• Only random single plasma levels without timing
• Urinary ketone levels
• Serum magnesium as the only necessary parameter

Correct Answer: Peak and trough plasma concentrations to minimize toxicity and ensure efficacy

Q24. Which pharmacy consideration is important when formulating topical neomycin products?

• Ensure compatibility with common topical excipients and avoid sulfhydryl compounds that may inactivate aminoglycosides
• Formulate only in nonpolar organic solvents because neomycin is lipophilic
• Always combine with systemic steroids to increase absorption
• Store only above 50°C to maintain potency

Correct Answer: Ensure compatibility with common topical excipients and avoid sulfhydryl compounds that may inactivate aminoglycosides

Q25. In preoperative bowel sterilization, neomycin is often combined with which agent for enhanced effect?

• Oral erythromycin to enhance anaerobic coverage
• Oral erythritol as an osmotic enhancer
• Oral metronidazole or a laxative regimen to reduce anaerobes and purge the bowel
• Intravenous amphotericin B for fungal prophylaxis

Correct Answer: Oral metronidazole or a laxative regimen to reduce anaerobes and purge the bowel

Q26. Which laboratory change would most likely be an early sign of aminoglycoside nephrotoxicity?

• Elevated transaminases
• Rising serum creatinine and decreased creatinine clearance
• Marked leukocytosis with left shift
• Hyperglycemia and ketonuria

Correct Answer: Rising serum creatinine and decreased creatinine clearance

Q27. Which statement about environmental stability of neomycin in aqueous formulations is most appropriate?

• Neomycin is extremely stable at all pH values and temperatures
• Neomycin stability depends on pH, temperature and presence of reactive excipients; suitable preservatives and pH control improve shelf life
• Neomycin must always be frozen for stability
• Neomycin decomposes instantly on contact with water

Correct Answer: Neomycin stability depends on pH, temperature and presence of reactive excipients; suitable preservatives and pH control improve shelf life

Q28. Which assay attribute is important when developing an HPLC method for neomycin?

• Use of a reverse‑phase column with appropriate ion‑pairing to retain the highly polar, cationic molecule
• Use of a nonpolar hexane mobile phase to solubilize neomycin
• Measurement by UV at 700 nm where neomycin has strong absorbance
• Avoid derivatization because neomycin is volatile

Correct Answer: Use of a reverse‑phase column with appropriate ion‑pairing to retain the highly polar, cationic molecule

Q29. Which clinical scenario is a contraindication or requires extreme caution with neomycin use?

• Topical application on intact skin in healthy adults
• Use in pregnancy due to potential fetal ototoxicity and systemic exposure
• Short‑term oral bowel decontamination in nonpregnant adults
• Use in topical ointment for minor cuts in adults without renal disease

Correct Answer: Use in pregnancy due to potential fetal ototoxicity and systemic exposure

Q30. Which combination therapy is pharmacologically rational when treating a severe gram‑positive enterococcal infection (synergistic approach)?

• Neomycin alone as monotherapy
• Aminoglycoside combined with a cell‑wall active agent (e.g., beta‑lactam) to enhance uptake and bactericidal activity
• Aminoglycoside combined with tetracycline for maximum bactericidal synergy
• Aminoglycoside combined with chloramphenicol to prevent resistance

Correct Answer: Aminoglycoside combined with a cell‑wall active agent (e.g., beta‑lactam) to enhance uptake and bactericidal activity

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com