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- This patient would most likely benefit from which of the following medications?
This patient would most likely benefit from which of the following medications?
Dr. Shoaib Ahmad Baig
January 19, 2025
🔍 Question
A previously healthy 45-year-old male undergoes an elective hernia repair under spinal anesthesia.
Postoperatively, he complains of difficulty voiding. Bladder catheterization shows a post-void residual of 300cc of urine.
This patient would most likely benefit from which of the following medications?
A. Finasteride
B. Phenylephrine
C. Bethanechol
D. Oxybutynin
E. Imipramine
Correct Answer 🎯:C. Bethanechol
⚙️
Initial Event: Surgery + Spinal Anesthesia
⬇
🔍 Blocks sacral nerves (S2-S4) (parasympathetic pathway 🛑)
⬇
⚙️ ↓ Parasympathetic input → ⚙️ Detrusor muscle relaxes 💤
⬇
⬇ Bladder contraction (like a deflated balloon 🎈)
⬆ Residual urine → POUR develops
🧠 Cholinergic agonist
⬇
⚙️ Activates M3 receptors on detrusor muscle
⬇
⬆ Bladder contraction strength (like refueling the engine of a weak car 🚗)
⬇
⬇ Residual urine → Improves voiding.
⚖️ Explanation of Other Differentials
Differential ⚖️ | Mechanism ⚙️ / Why Incorrect? 🔴 |
|---|---|
Finasteride | 🧠 Works by ⬇ conversion of testosterone to dihydrotestosterone (DHT ⚙️) → Useful in BPH (bucket overflow analogy 🪣), not acute POUR. |
Phenylephrine | 🧠 α-1 agonist → ⚙️ Constricts bladder neck sphincter (tightens the outlet 🚪) → Worsens retention. |
Oxybutynin | 🧠 Anticholinergic → ⚙️ Blocks M3 receptors → Further weakens detrusor contraction ⬇ (opposite of what’s needed here). |
Imipramine | 🧠 Tricyclic antidepressant → ⚙️ Anticholinergic side effects → Detrusor relaxation ⬇ → Worsens POUR. |
📝 Flashcards
Stay Hungry, Stay Curious!
Your Brother In This Struggle
Dr. Shoaib Ahmad
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