Sulfonamides Cotrimoxazole And Quinolones Question And Answers

Sulfonamides Cotrimoxazole And Quinolones Important Notes

1. Sulfonamides

  • hey have a structural resemblance to PABA
  • They compete with PABA for incorporation into folic acid
  • They act by inhibiting the enzyme folic acid synthetase which is essential for bacterial growth

Sulfonamides, Cotrimoxazole And Quinolones Uses:

  • Nocardial infection
  • Leprosy
  • Toxoplasmosis
  • Ulcerative colitis

Sulfonamides, Cotrimoxazole And Quinolones Adverse Effects:

  • Crystalluria
  • Haematuria, anuria
  • Kernicterus in newborns
  • Fixed drug eruption by sulfadiazine
  • Steven Johnson syndrome

2. Cotrimoxazole

  • It is a combination of Sulfamethoxazole and trimethoprim
  • It has a synergistic bacteriocidal effect
  • Dose: trimethoprim 80 mg + Sulfamethoxazole 400 mg
  • Uses:
  • Uncomplicated UTI
    • Respiratory infections
    • Gonorrhoea
    • Otitis media

3. Fluoroquinolones

  • Ciprofloxacin, ofloxacin, norfloxacin are fluoroquinolones
  • They are contraindicated in children as they cause Arthropathy and damage to developing cartilage
  • They are effective against facultative anaerobes
  • They inhibit the bacterial enzyme DNA gyrase

Sulfonamides Cotrimoxazole And Quinolones Long Essays

Question 1. Classify sulphonamides. Discuss the mechanism of action, adverse effects, And uses of cotrimoxazole.

Sulfonamides Classification:

  1. Short-acting – sulfadiazine.
  2. Intermediate-acting – sulfamethoxazole.
  3. Long-acting – sulfadoxine.
  4. Special purpose sulphonamide – Sulfasalazine, Silver sulfadiazine.


  • A combination of trimethoprim And sulfamethoxazole is called cotrimoxazole.

Cotrimoxazole Mechanism of action:

  • Cotrimoxazole causes sequential blockage of folic acid synthesis.

Sulfonamides Cotrimoxazole And Quinolones Contrimoxazole Mechanism Of Action

Read And Learn More: Pharmacology Question and Answers

Cotrimoxazole Uses:

  • Respiratory tract infections – tonsillitis, pharyngitis, sinusitis, bronchitis.
  • Urinary tract infections – acute And chronic.
  • Diarrhea And dysentery.
  • Typhoid, chancroid, granuloma inguinale.
  • Pneumocystis jiroveci pneumonia in AIDS patients.
  • Orodental infections.

Cotrimoxazole Adverse effects:

  • Nausea, vomiting, headache, stomatitis, rashes.
  • Precipitate megaloblastic anemia.
  • Blood disorders – anemia, granulocytopenia.
  • Uremia in patients with renal diseases.
  • Neonatal hemolysis And methemoglobinemia. When administered to pregnant women.

Question 2. Enumerate fluoroquinolones. Mention their antimicrobial spectrum, uses, And adverse effects.


  • These are quinolones antimicrobials having one or more fluorine substitutes.

Fluoroquinolones Classification:

Sulfonamides Cotrimoxazole And Quinolones Fluoroquinolones Classification

Antimicrobial spectrum:

1. Gram-positive organisms like

  • Staphylococci, chlamydiae, mycoplasma, And mycobacterium.

2. Gram-negative organisms like

  • Gonococci, meningococci, E-coli, salmonella, shigella, H. Pylori.

3. Some anaerobic organisms.

Antimicrobial spectrum Uses:

Sulfonamides Cotrimoxazole And Quinolones Antimicrobial Spectrum Uses

Antimicrobial spectrum Adverse effects:

  • Nausea, vomiting, abdominal discomfort, diarrhea, rashes.
  • Tendinitis.
  • Damage to growing cartilage
  • Headache, dizziness.
  • Precipitate seizures in epileptic patients.

Question 3. Classify drugs used in the treatment of infections caused by gram-negative organisms. Mention the mechanism of action of fluoroquinolones.

Fluoroquinolones Classification:

  • Drugs used in the treatment of infections caused by gram-negative organisms are:

1. B-lactam antibiotics

  • Penicillin, cephalosporin.

2. Tetracyclines – Doxycycline.

3. Aminoglycosides – Gentamicin, streptomycin.

4. Macrolides – erythromycin, Azithromycin.

5. Nitroimidazoles – Metronidazole.

6. Quinolones – Norfloxacin, Ciprofloxacin.

Fluorozuinolones (FQ):

Fluoroquinolones Mechanism of action:

  • DNA gyrase enzyme is required for DNA replication.
  • This enzyme has subunits A And B

Sulfonamides Cotrimoxazole And Quinolones Fluorozuinolones Mechanism Of Action

2. At low doses.

Sulfonamides Cotrimoxazole And Quinolones At Low Doses

Sulfonamides Cotrimoxazole And Quinolones Short Essays

Question 1. Write important side effects of sulphonamides.


  • Sulfonamides were the first effective antibacterial agents to be used systemically in man.
  • It contains a sulphonamide group.

Sulphonamides Adverse Effects:

1. GIT effects.

  • Nausea, vomiting, anorexia, abdominal pain.

2. Renal effects.

  • Renal irritation, hematuria, albuminuria. Crystalluria.
  • It occurs due to the precipitation of the drug in acidic urine.
  • Avoided by:
    • Intake of plenty of fluids.
    • Alkalinizing the urine with sodium bicarbonate.

3. Hypersensitivity reactions.

  • Fever, rashes, anaphylaxis, urticaria, and photosensitivity – occur rarely.
  • Stevens-Johnson syndrome And exfoliative dermatitis – occurs commonly.

4. Contact sensitization on topical application.

5. Hemolysis.

  • Occurs in patients with G6PD deficiency.

6. Kernicterus.

  • Occurs in newborns.
  • Sulfonamides displace bilirubin from binding sites.
  • This then crosses BBB And causes kernicterus.

Question 2. Sulfonamides are not very effective in the presence of pus. Explain.

Some bacteria synthesize their own folic acid which consists of p-amino benzoic acid (PABA).

  • Sulfonamide is structurally similar to PABA.
  • Thus it competitively inhibits the formation of folic acid.
  • Pus contains.
    • Purines And thymidine – which decreases the bacterial requirement for folic acid.
    • Antagonizes sulphonamide action.
    • It is rich in PABA.
    • Thus, sulphonamides are not very effective in the presence of pus.

Question 3. Explain the mechanism of action of co-trimoxazole.

The combination of trimethoprim And sulfamethoxazole is cotrimoxazole.

Co-trimoxazole Mechanism of action:

Sulfonamides Cotrimoxazole And Quinolones Co-trimoxazole Mechanism Of Action

  • Individual drugs are bacteriostatic.
  • While combination causes bacteriocidal action.
  • Through their combined effect sequential blockade of folic acid synthesis occurs.

Sulfonamides Cotrimoxazole And Quinolones Short Question And Answers

Question 1. Long-acting sulphonamides.

Long-acting sulphonamides are sulfadoxine And sul- famethopyrazine.

  • The action lasts for more than 1 week because of
    • High plasma protein binding.
    • Slow renal excretion.
  • They attain low plasma concentration so they are not suitable for the treatment of acute pyogenic infectious.

Long-acting sulphonamide Uses:

  • In malaria in combination with pyrimethamine.
  • Pneumocystis jiroveci pneumonia in AIDS patients.
  • Toxoplasmosis.

Long-acting sulphonamide Adverse Reaction:

  • Serious cutaneous reactions.

Question 2. The rationale of a combination of sulfamethoxazole with trimethoprim.

Sulfamethoxazole And trimethoprim are individually bacteriostatic

  • Sulfamethoxazole inhibits the conversion of PABA to dishy-dro folic acid while trimethoprim inhibits and prevents the reduction of dihydrofolate to tetrahydrofolate.
  • Thus, combining sulfamethoxazole And trimethoprim causes sequential blockade of folic acid synthesis And has bacteriocidal action.

Question 3. Ciprofloxacin.

Ciprofloxacin is first generation fluroquinolones.

  • It has a wide spectrum of activity
  • Has rapid bacteriocidal activity And high potency.
  • It is less active at acidic pH
  • It is rapidly absorbed orally.

Ciprofloxacin Uses:

  • Systemic infections.
  • Typhoid
  • Gonorrhoea.
  • Gastroenteritis.

Ciprofloxacin Adverse Reactions:

  • GIT effects – nausea, vomiting, anorexia.
  • CNS effects – Dizziness, headache, anxiety, insomnia, tremors.
  • Hypersensitivity reactions – rash, pruritis, photosensitivity, urticaria.
  • Tendonitis.

Question 4. Ciprofloxacin is contraindicated in children. Why?

Ciprofloxacin is fluoroquinolone.

  • It causes damage to the growing cartilage of weight-bearing joints.
  • This results in arthropathy.
  • Thus, it is contraindicated in children.

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