Pancuronium is a long-acting, non-depolarising aminosteroid NMJ blocker that competitively antagonises nicotinic ACh receptors.
It causes moderate vagolytic tachycardia, no histamine release, and stable BP, making it historically useful in cardiac anaesthesia.
Dose 0.06–0.1 mg/kg IV, duration 60–120 min, eliminated renally. Avoid in renal failure or tachyarrhythmia; reverse with neostigmine (not sugammadex).
# 1) Receptor-level action → clinical effects
**Class:** *Aminosteroid, long-acting, non-depolarising neuromuscular blocker (NDNMB)*
**Primary receptor action:**
* **Competitive antagonist** at **nicotinic acetylcholine receptors (nAChR)** at the **neuromuscular junction (NMJ)**.
* Prevents acetylcholine (ACh) binding to α-subunits → blocks Na⁺/K⁺ channel opening → prevents depolarisation and muscle contraction → **flaccid paralysis**.
**Additional receptor/system effects:**
* **Mild vagolytic (antimuscarinic) action at cardiac M₂ receptors** → **↑ HR**, **↑ MAP** (distinct from vecuronium).
* No histamine release → stable venodilation and no bronchospasm.
* **No ganglionic blockade** at therapeutic doses.
**Clinical effects derived:**
* Smooth, predictable paralysis.
* **Mild–moderate tachycardia and hypertension** (useful in cardiac anaesthesia during CPB weaning or when avoiding bradycardia).
* **Minimal effect on contractility** itself, but HR-driven ↑ CO.
---
# 2) Vial strength, preparation & basic pharmacokinetics (+ disadvantages)
**Formulation:**
* Commonly **2 mg/mL** (2 mL or 5 mL vials).
**Pharmacokinetics:**
* **Onset:** 2–3 min.
* **Peak effect:** 4–6 min.
* **Duration:** **60–120 min** (long-acting).
* **Half-life:** ~2 hours.
* **Metabolism:** hepatic (10–20%).
* **Excretion:** **80% renal**, minor biliary.
**Disadvantages (from PK/PD):**
* **Prolonged action** in renal failure.
* **Not ideal for short procedures or ICU infusions.**
* **Vagolysis** can cause tachycardia or hypertension in susceptible patients.
---
# 3) Practical dosing
## A. Anaesthesia (intubation & maintenance)
* **Intubation dose:** **0.06–0.1 mg/kg IV**.
* **Maintenance dose:** **0.01 mg/kg IV** every 40–60 min as needed.
* **Infusion (rarely used today):** 0.8–1.7 mcg/kg/min with TOF monitoring.
**Clinical onset/duration balance:**
* Onset similar to vecuronium, but recovery is 2–3× longer → not ideal for short surgeries.
* Residual blockade risk unless reversed.
**Useful context:**
* Cardiac anaesthesia (esp. in CABG or valve cases) where a **modest HR increase** helps maintain output during periods of high vagal tone.
* Avoid in tachyarrhythmias or hypertrophic cardiomyopathy.
## B. ICU
* **Rarely used** (due to prolonged duration, active renal excretion).
* If used (e.g., in renal-competent, haemodynamically bradycardic patients):
* **Bolus:** 0.06 mg/kg.
* **Infusion:** 0.8–1.7 mcg/kg/min (titrate to TOF 1–2 twitches).
---
# 4) Special populations — dosing cautions
### Pregnancy
* Crosses placenta minimally; used safely during C-section if needed.
* Slight prolongation of effect possible due to altered Vd.
### Lactation
* Minimal excretion into milk; short-term use acceptable.
### Hepatic impairment
* Slightly prolonged effect (reduced metabolism, biliary excretion).
* Titrate and monitor TOF.
### Renal impairment
* **Marked prolongation** of effect due to renal excretion → **avoid or reduce dose significantly**; consider **atracurium** or **cisatracurium** instead.
### Obesity
* Dose based on **Ideal Body Weight (IBW)** to prevent overdosing.
### Paediatrics
* **Dose:** 0.1 mg/kg IV (same ED95).
* Infants more sensitive; reduce dose slightly (0.05–0.08 mg/kg).
---
# 5) Drug interactions (clinically key)
**Potentiation (prolonged effect):**
* **Volatile agents:** sevoflurane, desflurane, isoflurane.
* **Aminoglycosides, clindamycin, tetracyclines:** inhibit ACh release.
* **MgSO₄, Ca²⁺ channel blockers, lithium:** depress ACh release → enhanced block.
* **Hypokalaemia, hypocalcaemia, acidosis, hypothermia:** prolong blockade.
**Antagonism (shortened effect):**
* **Chronic anticonvulsants (phenytoin, carbamazepine)** → resistance.
* **Burn injury, prolonged immobilisation** → receptor upregulation → resistance.
**Reversal interactions:**
* **Neostigmine (with atropine/glycopyrrolate)** → restores ACh competition.
* **Sugammadex:** *ineffective* (not suitable for pancuronium — works only on aminosteroids with specific molecular encapsulation pattern like vecuronium, rocuronium; pancuronium has different side chain conformation).
---
# 6) Significant complications & management
| Complication | Mechanism / Features | Management |
| ------------------------------ | ----------------------------------------- | --------------------------------------------------------------------------------------- |
| **Tachycardia / Hypertension** | Vagal (M₂) blockade → HR↑ | Usually mild; monitor; avoid in ischaemic heart disease; β-blocker (esmolol) if severe. |
| **Prolonged paralysis** | Renal accumulation, volatile potentiation | Reduce dose; monitor TOF; reversal with neostigmine. |
| **Residual curarisation** | Inadequate reversal / prolonged effect | Ensure TOF ≥0.9 before extubation; give reversal agents. |
| **Critical illness myopathy** | Prolonged use with steroids | Avoid >48 h infusion; supportive care, physiotherapy. |
| **Anaphylaxis (rare)** | IgE-mediated | Treat per anaphylaxis protocol (adrenaline, fluids, airway). |
---
# 7) Monitoring
* **Train-of-Four (TOF):**
* 1–2 twitches = surgical relaxation.
* ≥3 twitches = safe for reversal.
* TOF ratio ≥0.9 = safe extubation.
* **Haemodynamic monitoring:** tachycardia/hypertension due to vagolysis; ECG in cardiac patients.
---
Would you like to go next with **Rocuronium** (rapid-onset, suxamethonium alternative) or **Atracurium** (organ-independent elimination, ICU-friendly)?
No comments:
Post a Comment