AIM STEP 10 • STUDENT MEMORY SUPPORT
Student Memory Support
Fluoroquinolones, Sulfonamides and Trimethoprim
3rd Year MBBS • Infection and Inflammation • High-yield revision and memory reinforcement
1. High-Yield Flashcards
Tap each question to reveal the answer.
Which bacterial enzymes are targeted by fluoroquinolones?
DNA gyrase and topoisomerase IV.
What type of antibacterial action do fluoroquinolones produce?
Bactericidal, concentration-dependent killing.
Which fluoroquinolones are commonly classified as respiratory quinolones?
Levofloxacin and moxifloxacin.
Which fluoroquinolone has particularly important antipseudomonal activity?
Ciprofloxacin.
What is the approximate half-life of moxifloxacin?
About 12 hours.
Why is moxifloxacin not preferred when high urinary concentrations are required?
It undergoes substantial non-renal elimination and achieves relatively limited urinary exposure.
What is the principal mechanism of fluoroquinolone resistance?
Mutation of DNA gyrase or topoisomerase IV.
Which substances can reduce oral fluoroquinolone absorption by chelation?
Calcium, magnesium, aluminum and iron.
Which enzyme is inhibited by sulfonamides?
Dihydropteroate synthase.
Which normal bacterial metabolite is mimicked by sulfonamides?
Para-aminobenzoic acid (PABA).
Which enzyme is inhibited by trimethoprim?
Bacterial dihydrofolate reductase.
Why is sulfamethoxazole combined with trimethoprim?
To produce sequential blockade of bacterial folate synthesis and greater antibacterial activity.
Which important infection is treated with trimethoprim-sulfamethoxazole?
Pneumocystis jirovecii infection.
Which patients are at particular risk of sulfonamide-induced hemolysis?
Patients with G6PD deficiency.
Why can sulfonamides cause kernicterus in neonates?
They displace bilirubin from albumin, increasing free bilirubin that can enter the immature brain.
Which electrolyte disturbance can occur with trimethoprim?
Hyperkalemia.
How can sulfonamides affect phenytoin therapy?
They can increase phenytoin exposure and raise the risk of toxicity.
2. Mnemonics
Mnemonic Title: Fluoroquinolone Core Toxicities
Mnemonic Word: TEND-Q
Meaning: Tendon injury, Effects on CNS, Neuropathy, Dysglycemia, QT prolongation.
Mnemonic Title: Sulfonamide Major Adverse Effects
Mnemonic Word: HACK
Meaning: Hypersensitivity/hemolysis, Albumin displacement, Crystalluria, Kernicterus.
Mnemonic Title: Sequential Folate Blockade
Mnemonic Word: STEPS
Meaning: Sulfamethoxazole blocks the first enzyme step, then Trimethoprim blocks the next step in bacterial folate synthesis.
3. Memory Tables
Fluoroquinolones vs Sulfonamides vs Trimethoprim
| Feature | Fluoroquinolones | Sulfonamides | Trimethoprim |
|---|---|---|---|
| Main target | DNA gyrase / topoisomerase IV | Dihydropteroate synthase | Dihydrofolate reductase |
| Main process | DNA replication | Early folate synthesis | Later folate metabolism |
| Key memory clue | Concentration-dependent killing | PABA analogue | Sequential partner in co-trimoxazole |
Ciprofloxacin vs Respiratory Fluoroquinolones
| Feature | Ciprofloxacin | Levofloxacin / Moxifloxacin |
|---|---|---|
| Spectrum emphasis | Strong gram-negative activity | Improved pneumococcal activity |
| High-yield use clue | Pseudomonas coverage | Respiratory infections |
| Important distinction | Earlier fluoroquinolone | Respiratory fluoroquinolones |
4. Rapid Revision Points — Last-Minute Revision
Must Remember:
- Fluoroquinolones inhibit DNA gyrase and topoisomerase IV.
- Their antibacterial effect is bactericidal and concentration-dependent.
- Levofloxacin and moxifloxacin are respiratory fluoroquinolones.
- Moxifloxacin half-life is about 12 hours.
- Ciprofloxacin is important for antipseudomonal activity.
- Metal-containing antacids and supplements reduce fluoroquinolone absorption by chelation.
- Sulfonamides inhibit dihydropteroate synthase; trimethoprim inhibits dihydrofolate reductase.
- Co-trimoxazole produces sequential blockade of bacterial folate synthesis.
- Sulfonamides may cause hypersensitivity, crystalluria, G6PD-related hemolysis and kernicterus.
- Trimethoprim may cause folate-related marrow effects and hyperkalemia.
KMU Exam Trap: Do not confuse the two folate targets: sulfonamides block dihydropteroate synthase; trimethoprim blocks dihydrofolate reductase.
5. Clinical Memory Hooks
Pneumococcal respiratory infection → think levofloxacin or moxifloxacin because of improved respiratory gram-positive activity.
New tendon pain during fluoroquinolone therapy → suspect fluoroquinolone-associated tendinopathy.
Sulfonamide use in G6PD deficiency → increased risk of oxidative hemolysis.
Neonate exposed to a sulfonamide → bilirubin displacement from albumin → kernicterus risk.
Stable phenytoin patient develops toxicity after a sulfonamide → increased phenytoin exposure from reduced clearance / altered binding.
6. Starred High-Yield Exam Points
- ⭐ Fluoroquinolones inhibit DNA gyrase and topoisomerase IV.
- ⭐ Levofloxacin and moxifloxacin are respiratory fluoroquinolones.
- ⭐ Moxifloxacin half-life is about 12 hours and it has substantial non-renal elimination.
- ⭐ Sulfonamides inhibit dihydropteroate synthase; trimethoprim inhibits dihydrofolate reductase.
- ⭐ Co-trimoxazole works by sequential blockade of bacterial folate metabolism.
- ⭐ Sulfonamides can cause hemolysis in G6PD deficiency and kernicterus in neonates.
- ⭐ Sulfonamides can increase phenytoin toxicity by increasing active drug exposure.