Source / episode info
- **Episode:**33
- **Title:**Divine Intervention Episode 33 – Antibiotics Part 3 (Antibacterials).
- **Published:**2018-05-27
- Source:Episode page
One-liner
This episode reviews key antibacterial agents including the RIPE regimen for TB (emphasizing INH-induced B6 depletion), folate antagonists like sulfonamides and TMP-SMX, fluoroquinolones (and their pregnancy risks), and drugs used for PCP prophylaxis.
High-yield summary
- Isoniazid (INH): Inhibits the bacterial enzyme inhA (involved in mycolic acid synthesis). It is a pro-drug activated by Catalase Peroxidase, but its major side effects are B6 depletion, leading to seizures and peripheral neuropathy.
- Sulfonamides/TMP-SMX: These drugs inhibit folate synthesis at two sequential steps (dihydropteroate synthetase and dihydrofolate reductase). They are bacteristatic when used in combination with a DHFR inhibitor.
- Fluoroquinolones: Work by inhibiting bacterial DNA gyrase and Topoisomerase II, leading to supercoiling stress and cell death. They are contraindicated in pregnancy due to risk of cartilage deposition.
- G6PD Deficiency: Sulfonamides (e.g., Dapsone) and other oxidizing agents can precipitate acute hemolytic anemia because the patient lacks sufficient G6PD to regenerate NADPH for glutathione reductase, leading to oxidative stress.
- PCP Prophylaxis: First-line options include TMP-SMX, but alternatives include Dapsone, Pentamidine, or Atovaquone/Mekanamycin.
Learning objectives
- Describe the mechanism of action and major toxicities associated with first-line anti-tuberculosis drugs (INH, Rifampin).
- Explain the rationale for co-administering pyridoxine (Vitamin B6) when using INH.
- Differentiate between the mechanisms of folate synthesis inhibition by sulfonamides and trimethoprim/sulfamethoxazole.
- Identify contraindications for fluoroquinolones in pregnancy and explain the mechanism of toxicity.
- Recognize the risk of drug-induced oxidative stress (e.g., G6PD deficiency) associated with oxidizing antibiotics like Dapsone.
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