## Neuromuscular Mechanism: Depolarizing vs Non-Depolarizing Blockade **Key Point:** The fundamental distinction between succinylcholine and rocuronium lies in their mechanism at the acetylcholine receptor. Succinylcholine is a **depolarizing agent** (mimics acetylcholine, causes sustained depolarization); rocuronium is a **non-depolarizing agent** (competitive antagonist, blocks acetylcholine binding). ### Mechanism Comparison | Aspect | Succinylcholine (Depolarizing) | Rocuronium (Non-Depolarizing) | |--------|--------------------------------|-------------------------------| | **Receptor Interaction** | Agonist; binds & activates nAChR | Antagonist; blocks nAChR competitively | | **Channel Status** | Opens channel, sustains depolarization | Prevents channel opening | | **Fasciculations** | Present (visible muscle twitching) | Absent | | **Phase** | Phase I (depolarizing); Phase II (desensitization) | Non-depolarizing throughout | | **Reversibility** | Enzymatic hydrolysis (pseudocholinesterase) | Reversal with sugammadex or neostigmine | | **Potassium Release** | Marked (risk of hyperkalemia) | Minimal | **High-Yield:** Succinylcholine's depolarization causes visible **fasciculations** (brief muscle contractions before paralysis), which can increase intragastric pressure, intraocular pressure, and serum potassium. Rocuronium causes no fasciculations because it simply blocks the receptor without activating it. **Clinical Pearl:** Succinylcholine fasciculations can be attenuated by pre-treatment with a small dose of non-depolarizing agent (defasciculation), but this delays RSI onset. In RSI, fasciculations are usually accepted as a trade-off for rapid paralysis. **Mnemonic:** **SUCC = Agonist (mimic ACh), ROCU = Antagonist (block ACh)** — Succinylcholine mimics acetylcholine and activates the receptor; rocuronium blocks acetylcholine from binding.
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