Source / episode info
- **Episode:**545
- **Title:**Divine Intervention Episode 545: USMLE Step 2CK/3 Rapid Review Series 116
- **Published:**2024-08-07
- Source:Episode page
One-liner
This episode is a rapid review emphasizing the specific order of tinea species (Trichophyton, Microsporum, Epidermophyton), the critical importance of CYP450 enzyme induction in drug interactions (e.g., Warfarin, Vitamin D), and high-yield associations for autoimmune vasculitis treated with steroids and cyclophosphamide.
High-yield summary
- Tinea Species Order: The three species to memorize are Trichophyton (most common), Microsporum, and Epidermophyton.
- Antifungal Choice: For tinea involving the nails or scalp, systemic antifungals (Terbinafine is preferred) must be used; topical agents are insufficient.
- CYP450 Principle: Drugs that induce CYP450 (e.g., Griseofulvin, Carbamazepine, Rifampin, Phenytoin, St. John's Wort) accelerate the metabolism of other drugs metabolized by this system, leading to therapeutic failure and potential complications (e.g., reduced Warfarin effect).
- Anticoagulation Monitoring: In patients on warfarin for atrial fibrillation or mechanical valves, adding a CYP450 inducer can cause subtherapeutic INR levels, increasing the risk of thromboembolism/stroke.
- IPF Location: Idiopathic Pulmonary Fibrosis (IPF) has a predilection for the bases of the lungs.
- Autoimmune Combinations: The combination of steroids and cyclophosphamide is used to treat Polyarteritis Nodosa, Wegener's Granulomatosis, Churg-Strauss Syndrome, and Goodpasture Syndrome.
Learning objectives
- Identify the three species of dermatophytes causing tinea infections in correct order of prevalence.
- Select appropriate systemic antifungal agents for tinea involving keratinized tissue (nails/scalp) while considering drug interactions.
- Explain the mechanism and clinical consequences of CYP450 enzyme induction on drugs like Warfarin, Vitamin D, and oral contraceptives.
- Recognize the classic pulmonary pattern and location associated with Idiopathic Pulmonary Fibrosis (IPF).
- List the four autoimmune vasculitis syndromes treated with a combination of steroids and cyclophosphamide.