Pancuronium

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)?

Vecuronium

 Excellent — here’s **Vecuronium**, a key non-depolarising neuromuscular blocker, presented in your structured anaesthesia–ICU learning format with both molecular and clinical depth.

---

# 1) Receptor-level action → clinical effects

**Class:** *Aminosteroid, non-depolarising neuromuscular blocker (NDNMB).*

**Primary receptor action:**

* **Competitive antagonist** at **nicotinic acetylcholine receptors (nAChR)** at the **neuromuscular junction (NMJ)**.

* Competes with acetylcholine (ACh) for the α-subunits of the nAChR, preventing ion channel opening → no depolarisation → **flaccid paralysis**.

**Additional receptor/system effects:**

* **No effect on muscarinic receptors** → **no tachycardia or bronchospasm.**

* **No histamine release** → minimal hypotension or flushing.

* **No autonomic ganglion blockade.**

* Slight central nicotinic receptor effect if high doses (clinically insignificant).

**Clinical consequences:**

* Smooth, predictable paralysis with **stable haemodynamics.**

* Ideal for **cardiac surgery, ICU ventilation, and neuro cases**.

* **Reversible** by acetylcholinesterase inhibitors (e.g., neostigmine) or **sugammadex** (specific binding reversal).

---

# 2) Vial strength, preparation & basic pharmacokinetics (+ disadvantages)

**Presentation:**

* **10 mg lyophilised powder vial** (reconstitute with 5 mL sterile water → 2 mg/mL).

* **Supplied as bromide salt** (vecuronium bromide).

**Pharmacokinetics:**

* **Onset:** 2–3 min.

* **Peak:** 3–5 min.

* **Duration:** 25–40 min (intermediate-acting).

* **Elimination half-life:** 60–90 min.

* **Metabolism:** hepatic deacetylation → **3-desacetyl-vecuronium (active metabolite)**.

* **Excretion:** biliary (75%), renal (25%).

**Disadvantages (from PK):**

* **Prolonged action** in hepatic/renal impairment due to accumulation.

* **Slower onset** than rocuronium or suxamethonium.

* **No vagolysis or histamine release** → may not counteract opioid/volatile-induced bradycardia.

---

# 3) Practical dosing

## A. Anaesthesia (intubation & maintenance)

* **Intubation dose:** **0.08–0.1 mg/kg IV** (≈ 6–7 × ED95).

  * *Onset:* 2–3 min → slower than suxamethonium/rocuronium.

  * *Duration:* 25–40 min.

* **Maintenance dose:** **0.01–0.02 mg/kg IV** bolus as required or **infusion 1–2 mcg/kg/min**.

* **Priming dose (optional):** 0.01 mg/kg (10% of intubation dose) 3–5 min before induction for faster onset.

## B. ICU (prolonged ventilation / paralysis)

* **Initial bolus:** 0.1 mg/kg.

* **Maintenance infusion:** **0.8–1.7 mcg/kg/min**, titrated to Train-of-Four (TOF 1–2 twitches).

* Avoid prolonged infusions >24–48 h if possible → **critical illness myopathy/neuropathy** risk, esp. with corticosteroids.

**Compatibility:** dilute in 0.9% saline or 5% dextrose; stable for 24 h at room temperature.

---

# 4) Special populations — dosing cautions

### Pregnancy

* Crosses placenta minimally; used safely for caesarean section (no fetal depression).

* Slightly prolonged effect postpartum due to hormonal changes.

### Lactation

* Minimal transfer to breast milk; safe after emergence.

### Hepatic impairment

* **Prolonged duration** due to decreased metabolism and biliary excretion → reduce maintenance dose, monitor TOF closely.

### Renal impairment

* Accumulation of active metabolite (3-desacetyl-vecuronium) → **prolonged paralysis**.

* Use lower infusion rates or prefer **atracurium/cisatracurium** (Hoffmann elimination).

### Obesity

* Dose based on **Ideal Body Weight (IBW)** to avoid overdosing.

### Paediatrics

* **Dose:** 0.1 mg/kg IV (same ED95); shorter duration due to higher clearance in young children.

* Neonates more sensitive → reduce dose (0.05–0.08 mg/kg).

---

# 5) Drug interactions (clinically key)

**Potentiation (enhanced block):**

* **Volatile anaesthetics** (esp. sevo/des/iso) – augment NMJ blockade.

* **Aminoglycosides, clindamycin, tetracyclines** – inhibit ACh release.

* **MgSO₄, Ca²⁺ channel blockers, local anaesthetics, lithium** – depress ACh release/excitation–contraction coupling.

* **Hypothermia, acidosis, hypokalaemia, hypocalcaemia** – prolong paralysis.

**Antagonism (reduced effect):**

* **Chronic phenytoin or carbamazepine** use → enzyme induction, resistance to block.

* **Burn injury, hemiplegia/paraplegia, myasthenia gravis remission** → receptor upregulation, increased resistance.

**Reversal interactions:**

* **Neostigmine** (with atropine/glycopyrrolate) → restores ACh levels; only once TOF ≥2.

* **Sugammadex** (specific for aminosteroids: vecuronium, rocuronium) → rapid encapsulation and reversal.

---

# 6) Significant complications & management

| Complication                            | Mechanism / Features                                               | Management                                                                                         |

| --------------------------------------- | ------------------------------------------------------------------ | -------------------------------------------------------------------------------------------------- |

| **Prolonged neuromuscular block**       | Accumulation or potentiation (renal/hepatic failure, drug synergy) | Neuromuscular monitoring; reversal with **neostigmine** or **sugammadex**; supportive ventilation. |

| **Critical illness myopathy**           | Prolonged infusion + corticosteroids                               | Minimise duration; avoid unnecessary paralysis; physiotherapy post-ICU.                            |

| **Residual paralysis / awareness risk** | Inadequate reversal                                                | TOF monitoring, reversal agent, clinical check (head lift, tidal volume).                          |

| **Anaphylaxis (rare)**                  | IgE-mediated                                                       | Stop drug; treat with **adrenaline**, fluids, airway management.                                   |

---

## 7) Monitoring

* **Neuromuscular monitoring (TOF):**

  * 4:0 = full recovery

  * 4:1–2 = adequate for reversal

  * 1–2 twitches = ideal for surgery

  * 0 twitches = deep block (avoid prolonged period in ICU)

---

## Pocket viva line

*Vecuronium is an **aminosteroid non-depolarising NMJ blocker** causing **competitive antagonism at nicotinic ACh receptors**. It produces smooth paralysis with stable haemodynamics, **no histamine release**, and is **reversible with neostigmine or sugammadex**.

Dose **0.08–0.1 mg/kg IV** for intubation, **0.01–0.02 mg/kg** for maintenance, or **1 mcg/kg/min** infusion in ICU. Duration **25–40 min**, prolonged in hepatic/renal dysfunction.*

---

Would you like me to continue next with **Rocuronium** (fast-onset aminosteroid and suxamethonium alternative) or **Atracurium** (benzylisoquinolinium, Hofmann-eliminated, ICU-friendly)?

Amiodarone

Amiodarone is a **multi-class anti-arrhythmic** (mainly **Class III**) blocking K⁺, Na⁺, β, and Ca²⁺ channels. 

It **prolongs repolarisation**, slows AV conduction, and treats both **atrial and ventricular arrhythmias** with low torsades risk.

IV: **150 mg over 10 min**, then **1 mg/min × 6 h**, then **0.5 mg/min**; oral maintenance **100–200 mg/day**.

Toxicities: thyroid, pulmonary, hepatic, ocular, neurologic. 

Monitor LFTs, TFTs, ECG, CXR periodically.

---

# 1) Receptor-level action → clinical effects

**Class:** *Class III anti-arrhythmic (broad-spectrum)*

**Receptor / channel effects (multi-class):**

| Mechanism                 | Target                                  | Effect                                                         | Vaughan-Williams class |

| ------------------------- | --------------------------------------- | -------------------------------------------------------------- | ---------------------- |

| **K⁺-channel blockade**   | Delayed rectifier K⁺ current            | ↑ repolarisation time, ↑ refractory period → prevents re-entry | **III**                |

| **Na⁺-channel blockade**  | Fast inward Na⁺ current (use-dependent) | ↓ conduction velocity                                          | **I**                  |

| **β-blockade**            | β₁, β₂ antagonism                       | ↓ HR, ↓ AV nodal conduction                                    | **II**                 |

| **Ca²⁺-channel blockade** | L-type channels                         | ↓ AV nodal conduction, negative inotropy                       | **IV**                 |

**Net electrophysiologic effects**

* **Prolonged action potential duration** (QT↑ but *low torsades risk*).

* **Slows SA and AV node conduction**, suppresses ectopic foci.

* **Stabilises re-entry and automatic tachyarrhythmias** in atrial and ventricular tissue.

**Clinical outcomes**

* Broad anti-arrhythmic: effective for **AF**, **atrial flutter**, **SVT**, **VT**, **VF** (esp. refractory or post-CPB).

* **Haemodynamic profile:** mild vasodilation, negative inotropy minimal (better tolerated in LV dysfunction).

* **Heart-rate control** + rhythm conversion capabilities.

---

# 2) Vial strength, preparation & basic pharmacokinetics (+ disadvantages)

**IV formulation:** 150 mg/3 mL (50 mg/mL) in polysorbate solvent (non-PVC set required).

**Oral tablets:** 100 mg, 200 mg.

**Pharmacokinetics**

* **Onset (IV):** 2–5 min for rate control; 1–2 h for rhythm conversion.

* **Half-life:** biphasic — early 3–10 h; terminal **weeks (20–100 days)** → extensive tissue accumulation.

* **Metabolism:** hepatic via **CYP3A4 → desethyl-amiodarone (active)**.

* **Excretion:** biliary; negligible renal elimination.

* **Highly lipophilic** → large Vd; slow clearance.

**Disadvantages**

* **Very long half-life** → delayed toxicity reversal.

* **Multiple organ toxicities** with chronic use.

* **Hypotension and bradycardia** with rapid IV loading (solvent & vasodilation).

---

# 3) Practical dosing

## A. Anaesthesia / Cardiac theatre

**Indications:** peri-operative **AF**, **VT**, **VF**, **post-CPB arrhythmia prophylaxis**.

* **IV loading:** 150 mg over **10 min** (dilute in 100 mL 5% Dextrose).

* **Then infusion:**

  * **1 mg/min (60 mg/h)** for 6 h → then **0.5 mg/min (30 mg/h)** for 18 h or until rhythm stabilises (total 900–1200 mg/24 h).

* **Refractory VT/VF (ACLS):**

  * **300 mg IV push** (undiluted) → may repeat **150 mg** once after 3–5 min if VF/pulseless VT persists.

* **Post-bypass prophylaxis:** 150 mg slow bolus at re-perfusion ± infusion 0.5–1 mg/min for 6–12 h.

## B. ICU / Ward maintenance

* **Oral loading:** 200 mg TDS for 1 week → 200 mg BD for 1 week → 100–200 mg daily maintenance.

* **Transition from IV to PO** once stable rhythm achieved.

---

# 4) Special populations — dosing cautions

### Pregnancy

* Crosses placenta → risk of **fetal hypothyroidism, bradycardia**. Use only if life-threatening arrhythmia.

### Lactation

* Excreted in milk → avoid breastfeeding while on therapy.

### Hepatic impairment

* **Reduce dose / monitor LFTs**; hepatotoxicity possible with accumulation.

### Renal impairment

* *No dose adjustment* — not renally cleared.

### Obesity

* Highly lipophilic → large Vd, prolonged accumulation; avoid excessive long-term loading.

### Paediatrics

* **Loading:** 5 mg/kg over 20–60 min (max 300 mg), repeat q8 h PRN (max 15 mg/kg/day).

* **Infusion:** 10–15 mcg/kg/min for maintenance.

---

# 5) Drug interactions (clinically key)

* **Warfarin:** inhibits metabolism → ↑ INR → halve warfarin dose, monitor closely.

* **Digoxin:** doubles serum digoxin → halve digoxin dose, monitor ECG/K⁺.

* **Statins (simvastatin, atorvastatin):** ↑ myopathy risk → use lower dose/rosuvastatin preferred.

* **β-blockers / CCBs:** additive bradycardia, AV block, hypotension.

* **QT-prolonging drugs** (fluoroquinolones, macrolides, azoles, antipsychotics): additive torsades risk (though amiodarone’s torsades risk is low).

* **CYP3A4 inhibitors (azoles, macrolides, protease inhibitors, grapefruit):** ↑ toxicity.

* **CYP inducers (phenytoin, rifampicin):** ↓ efficacy.

* **Anaesthetic volatile agents:** additive bradycardia, hypotension.

---

# 6) Significant complications & management

| System           | Complication / mechanism                                                                        | Monitoring / Management                                                            |

| ---------------- | ----------------------------------------------------------------------------------------------- | ---------------------------------------------------------------------------------- |

| **Cardiac**      | Bradycardia, AV block, hypotension (IV solvent)                                                 | Slow/stop infusion; **atropine**, **isoprenaline**, temporary pacing if needed.    |

| **Pulmonary**    | Interstitial pneumonitis / fibrosis (dose-related, chronic)                                     | Baseline + periodic CXR & PFTs; stop drug; corticosteroids if severe.              |

| **Thyroid**      | Contains iodine → **hypothyroidism** (inhibition of T₄→T₃) or **hyperthyroidism** (Jod-Basedow) | Monitor **TFTs q6 months**; treat accordingly (thyroxine / carbimazole ± steroid). |

| **Hepatic**      | Hepatitis, ↑ LFTs                                                                               | Baseline + periodic **LFTs**; stop if >3× ULN.                                     |

| **Ocular**       | Corneal microdeposits (benign) / optic neuritis (rare)                                          | Annual eye exam; discontinue if visual loss.                                       |

| **Dermatologic** | Blue-grey skin discolouration, photosensitivity                                                 | Sun protection; usually cosmetic.                                                  |

| **Neurologic**   | Tremor, ataxia, peripheral neuropathy                                                           | Dose reduction or cessation.                                                       |

| **Electrolyte**  | Hypo-/hyper-thyroid effects alter cardiac response                                              | Monitor K⁺, Mg²⁺, TFTs.                                                            |

---

Magnesium Sulphate (MgSO₄)

Magnesium sulphate is a **physiological Ca²⁺ antagonist** and **NMDA blocker** providing **anti-arrhythmic**, **anticonvulsant**, **vasodilator**, and **bronchodilator** effects. 

It treats **torsades de pointes**, **digoxin toxicity**, **eclampsia**, and **hypomagnesaemia**, and blunts catecholamine response post-CPB. 

Typical dose: **1–2 g IV over 10–15 min**, maintenance **0.5–1 g/h**; monitor reflexes, RR, and serum Mg, especially in renal impairment.

# 1) Receptor-level action → clinical effects

**Primary mechanisms:**

Magnesium is a **physiological calcium antagonist** and **membrane stabiliser**. It modulates several receptor systems:

| Target                                            | Effect                                                 | Clinical implication                                                   |

| ------------------------------------------------- | ------------------------------------------------------ | ---------------------------------------------------------------------- |

| **Voltage-gated Ca²⁺ channels**                   | ↓ Ca²⁺ influx into presynaptic and smooth-muscle cells | Vasodilation, anti-arrhythmic, tocolytic, anticonvulsant               |

| **NMDA receptor (non-competitive antagonist)**    | ↓ excitatory glutamate activity                        | Anticonvulsant, neuroprotection, analgesic adjunct                     |

| **Na⁺/K⁺-ATPase / Na⁺ channels**                  | Membrane stabilisation                                 | Anti-arrhythmic effect                                                 |

| **ACh release at neuromuscular junction**         | ↓ ACh release → reduced transmission                   | Potentiates neuromuscular blockade                                     |

| **Catecholamine release (adrenal + sympathetic)** | Inhibition                                             | Anti-tachyarrhythmic, ↓ stress response                                |

| **Myocardium**                                    | Mild negative inotropy                                 | Useful in tachyarrhythmias but may cause hypotension in fragile hearts |

**Summary of clinical effects**

* **Cardiovascular:** vasodilation (↓ SVR, ↓ PVR), ↓ catecholamine surge, stabilises myocardium, treats torsades de pointes and digoxin toxicity.

* **CNS:** anticonvulsant (e.g., eclampsia), mild sedation, neuroprotective.

* **Respiratory:** bronchodilation (asthma, status asthmaticus adjunct).

* **Neuromuscular:** potentiates relaxants; overdose → loss of reflexes, respiratory paralysis.

---

# 2) Vial strength, preparation & basic pharmacokinetics (+ disadvantages)

**Formulations:**

* Common: **50% solution = 500 mg/mL** (each mL = 4 mmol Mg²⁺).

* Dilute in 0.9% saline or 5% dextrose for IV use.

**Pharmacokinetics:**

* **Onset (IV):** immediate.

* **Duration:** 30 min–2 h (depending on renal clearance).

* **Distribution:** extracellular and intracellular compartments (slow equilibration).

* **Elimination:** **renal** (95%).

* **Half-life:** ~4 h (normal kidneys), prolonged in renal impairment.

**Disadvantages:**

* Requires **IV titration**; narrow therapeutic-to-toxic window.

* **Hypotension, bradycardia, muscle weakness, respiratory depression** in overdose.

* **Accumulation** in renal failure.

---

# 3) Practical dosing

## A. Anaesthesia / Cardiac practice

**Indications:**

* **Arrhythmias** (torsades de pointes, digoxin-induced VT/VF, refractory VF).

* **Attenuation of catecholamine stress** response to laryngoscopy or CPB.

* **Pulmonary hypertension** (↓ PVR).

* **Post-bypass atrial/ventricular arrhythmia prophylaxis.**

**Typical dosing:**

* **Bolus:** 1–2 g IV (≈ 8–16 mmol) over 10–15 min (dilute in 50 mL 0.9% NaCl).

* **Arrhythmia (torsades):** 2 g IV over 1–2 min (may repeat once in 5–15 min).

* **Infusion (maintenance):** 1–2 g/h (4–8 mmol/h) titrated to effect.

* **Max daily dose:** ~8–12 g in adults (unless in severe eclampsia protocols).

**Post-bypass example:** 2 g (8 mmol) bolus after declamping → reduces arrhythmias, blunts catecholamine surge, smooths extubation.

## B. ICU

**Indications:**

* Torsades de pointes, digoxin toxicity, eclampsia, severe asthma, hypomagnesaemia, refractory arrhythmias, pulmonary hypertension, tachyarrhythmia control in catecholamine excess.

* **Hypomagnesaemia replacement:**

  * Mild (serum 0.6–0.8 mmol/L): **2 g (8 mmol) IV over 1 h**.

  * Severe (<0.5 mmol/L): **4–8 g IV over 4–6 h**, then infusion 0.5–1 g/h.

  * Continuous infusion: **0.5–1 g/h (2–4 mmol/h)** to maintain serum 0.8–1.0 mmol/L.

---

# 4) Special populations — dosing cautions

### Pregnancy

* Widely used in **eclampsia**: 4 g IV load (over 5–10 min), then 1 g/h infusion (Pritchard or Zuspan regimens).

* Crosses placenta → transient neonatal hypotonia possible; monitor reflexes in neonate.

### Lactation

* Excreted into breast milk in small quantities; short-term maternal therapy considered safe.

### Hepatic impairment

* Not hepatically metabolised → **no adjustment needed.**

### Renal impairment

* **Major concern:** risk of accumulation/toxicity → **reduce dose by 50%**; monitor **reflexes, RR, urine output, serum Mg²⁺**.

* Avoid continuous infusions unless under strict monitoring.

### Obesity

* Dose by **actual body weight** up to 100 kg; after that, consider adjusted body weight for maintenance infusions.

### Paediatrics

* **Arrhythmia:** 25–50 mg/kg (max 2 g) over 10–20 min.

* **Maintenance:** 10–20 mg/kg/h (max 2 g/h).

* **Bronchodilator adjunct:** 25–75 mg/kg over 20 min (max 2 g).

---

# 5) Drug interactions (clinically key)

* **Neuromuscular blockers:** additive → **potentiates both depolarising (sux) and non-depolarising** relaxants → dose reduction needed.

* **Calcium channel blockers:** exaggerated **hypotension and heart block**.

* **Digoxin:** stabilises myocardium, but high Mg²⁺ may increase AV block.

* **Opioids / sedatives:** additive respiratory depression in overdose.

* **Loop/thiazide diuretics:** increase Mg loss → may require higher maintenance.

* **Lithium:** increased neurotoxicity risk.

---

# 6) Significant complications & management

| Complication                           | Mechanism / Features                  | Management                                                                   |

| -------------------------------------- | ------------------------------------- | ---------------------------------------------------------------------------- |

| **Hypotension, flushing**              | Vasodilation from Ca²⁺ blockade       | Slow infusion; fluids; vasopressor if severe.                                |

| **Bradycardia / heart block**          | SA/AV nodal depression                | Stop infusion; calcium gluconate 10% 10 mL IV slow push; atropine if needed. |

| **Respiratory depression / arrest**    | Neuromuscular blockade                | Stop drug, ventilate, give **calcium gluconate 10% 10–20 mL IV**.            |

| **Loss of reflexes / muscle weakness** | Early sign of toxicity (Mg >4 mmol/L) | Stop Mg; IV calcium; monitor RR, reflexes.                                   |

| **Hypermagnesaemia**                   | Accumulation in renal impairment      | Supportive; **calcium**, diuretics, dialysis if severe.                      |

**Toxicity thresholds:**

* Loss of reflexes: >4 mmol/L

* Respiratory paralysis: >5 mmol/L

* Cardiac arrest: >6 mmol/L

**Antidote:** 

Calcium gluconate 10% 10 mL IV over 5 min** (can repeat).

---

Milrinone

Milrinone, one of the most important inodilators for cardiac anaesthesia and ICU. 

Milrinone is a phosphodiesterase-III inhibitor that increases cAMP → inotropy + lusitropy + vasodilation (“inodilator”). 

It’s β-independent, useful post-CPB or in β-blocked hearts, but causes hypotension and arrhythmia, prolonged in renal failure.

Load **50 mcg/kg over 10 min**, infuse **0.25–0.75 mcg/kg/min** (reduce if renal impairment). Combine with **norepinephrine** when needed to maintain MAP.

---

# 1) Receptor-level action → clinical effects

**Primary mechanism:**

* **Selective phosphodiesterase-III (PDE-3) inhibitor** → prevents breakdown of cyclic AMP (cAMP) in **cardiac myocytes** and **vascular smooth muscle**.

**Resulting downstream effects:**

* ↑ **cAMP** → ↑ intracellular **Ca²⁺** availability in myocardium → **positive inotropy**.

* ↑ cAMP in vascular smooth muscle → ↓ intracellular Ca²⁺ → **vasodilation** (both systemic & pulmonary).

* Also enhances **lusitropy** (myocardial relaxation) → improves diastolic filling.

**Net clinical effects:**

* ↑ cardiac contractility and stroke volume (inotropy).

* ↓ preload and afterload (inodilator).

* ↓ pulmonary artery pressure & PVR (helpful in RV failure, post-CPB, pulmonary hypertension).

* **No direct chronotropic or β-receptor stimulation** → safe in β-blocked patients.

* Can cause **hypotension** if preload low.

---

# 2) Vial strength, preparation & basic pharmacokinetics (+ disadvantages)

**Vials:** 10 mg/10 mL (1 mg/mL).

**Typical infusion preparation:**

* Dilute **10 mg in 100 mL** (0.1 mg/mL).

**Pharmacokinetics:**

* **Onset:** 5–15 min (after bolus).

* **Peak:** ~10 min.

* **Duration:** 2–4 h after stopping (depends on renal function).

* **Elimination:** **renal (unchanged drug)**.

* **Half-life:** 2.3 h (normal renal function), **up to 10 h** if renal failure.

**Disadvantages:**

* **Hypotension** from vasodilation (especially if preload inadequate).

* **Arrhythmia risk** (ventricular > atrial, though less than adrenaline/dobutamine).

* **Prolonged action in renal impairment.**

---

# 3) Practical dosing

## A. Anaesthesia / Cardiac theatre

**Indications:** post-CPB low cardiac output, RV dysfunction, pulmonary hypertension, weaning from bypass, β-blockade blunting.

* **Loading dose:** 50 mcg/kg IV over 10 min (may omit if hypotensive).

* **Maintenance infusion:** **0.25–0.75 mcg/kg/min**, titrate by 0.1–0.2 increments.

* Start low if systemic BP borderline or patient hypovolaemic.

* If significant hypotension, combine with **norepinephrine** or **vasopressin**.

**Typical 70-kg patient:**

* Load 3.5 mg over 10 min, then start 0.3 mcg/kg/min → 1.26 mg/h → **12.6 mL/h** (if 0.1 mg/mL solution).

## B. ICU

**Indications:**

* Post-cardiac surgery LCOS, RV failure, pulmonary hypertension crisis, or severe systolic heart failure refractory to catecholamines.

**Dosing:**

* **0.25–0.75 mcg/kg/min**, titrate to cardiac index, ScvO₂, lactate, and filling pressures.

* Avoid bolus in unstable hypotensive patients.

* Combine with **vasopressor** if MAP <65 mmHg.

---

# 4) Special populations — dosing cautions

### Pregnancy

* Limited data; use only if benefit outweighs risk (e.g., severe heart failure or pulmonary hypertension in obstetric anaesthesia).

### Lactation

* Unknown excretion; avoid breastfeeding during continuous infusion; safe after discontinuation due to short exposure.

### Hepatic impairment

* Metabolism minimal → no major adjustment.

### Renal impairment

* **Reduce dose:**

  * CrCl 30–50 mL/min → 0.23 mcg/kg/min

  * CrCl 10–30 → 0.2 mcg/kg/min

  * CrCl <10 → 0.13 mcg/kg/min

* Avoid loading dose. Monitor for prolonged hypotension and arrhythmia.

### Obesity

* Dose on **Ideal/Adjusted Body Weight**; avoid overshoot due to hypotension risk.

### Paediatrics

* **Bolus:** 50 mcg/kg over 10 min.

* **Infusion:** 0.25–0.75 mcg/kg/min (same range).

* Neonates: prolonged half-life; start lower (0.25 mcg/kg/min).

---

# 5) Drug interactions (clinically key)

* **Loop diuretics (furosemide):** precipitate in same line — use separate lumen.

* **Other vasodilators (nitroglycerin, nitroprusside):** additive hypotension.

* **Catecholamines (dobutamine, adrenaline):** synergistic for inotropy—common combination in LCOS.

* **Beta-blockers:** effects preserved (not receptor-mediated).

* **Norepinephrine:** balances systemic BP; often co-infused.

* **Dopamine/dobutamine:** may further increase arrhythmia risk if used together long-term.

* **Digoxin:** additive arrhythmogenicity possible.

---

# 6) Significant complications & management

| Complication                          | Mechanism / Features                       | Management                                                                       |

| ------------------------------------- | ------------------------------------------ | -------------------------------------------------------------------------------- |

| **Hypotension**                       | Peripheral vasodilation from ↑ cAMP in VSM | Volume resuscitate; reduce rate; start vasopressor (norepi/vasopressin).         |

| **Ventricular arrhythmias**           | Excess cAMP, Ca²⁺ overload                 | Reduce/stop infusion; correct K⁺, Mg²⁺, acid-base; antiarrhythmics if sustained. |

| **Tachycardia / palpitations**        | Mild β₁ stimulation                        | Usually self-limiting; adjust dose.                                              |

| **Thrombocytopenia (rare)**           | Idiosyncratic                              | Stop drug; monitor platelets.                                                    |

| **Prolonged effect in renal failure** | Accumulation                               | Adjust dose; extend interval; consider CRRT clearance if severe.                 |

---

Adrenaline (Epinephrine)

Adrenaline is a potent **β₁/β₂/α₁ agonist** with **dose-dependent** inotropy, chronotropy, bronchodilation, and vasoconstriction. 

It’s the **drug of choice for anaphylaxis**, a powerful **inopressor** for LCOS/post-CPB or refractory septic vasoplegia, and the standard **ALS** vasopressor. 

Typical ICU/OR infusion **0.02–0.2 (up to 0.5) mcg/kg/min**; use central access and be vigilant for **arrhythmias, ischaemia, lactate rise, hypokalaemia**, and **extravasation injury.

# 1) Receptor-level action → clinical effects

**Primary receptors (dose-dependent):**

* **β₁ agonist** → ↑ inotropy, ↑ chronotropy, ↑ dromotropy → ↑ **CO**.

* **β₂ agonist** → **bronchodilation**, skeletal-muscle vasodilation, **↓ mast-cell mediator release**; metabolic effects (↑ glucose, **↓ K⁺** via cellular shift).

* **α₁ agonist** (more prominent at higher doses) → **arterial/venous vasoconstriction** → ↑ **SVR/MAP**.

**Clinical phenotype by dose (rule of thumb):**

* **Very low–low** (≤0.02–0.05 mcg/kg/min): β₁/β₂ dominant → ↑ CO, mild ↓ SVR.

* **Moderate** (0.05–0.2): balanced β + α → ↑ CO **and** ↑ SVR.

* **High** (>0.2): α₁ predominant → marked vasoconstriction; risk of ↑ afterload, ischaemia, lactate rise.

**Key bedside effects**

* **Heart:** powerful inotrope/chronotrope; may precipitate **AF/VT/VF**, ↑ myocardial O₂ demand → **ischaemia**.

* **Vessels:** dose-dependent vasoconstriction (skin/splanchnic) or vasodilation (muscle) → net MAP usually rises with moderate–high doses.

* **Lungs:** **bronchodilation**; cornerstone for **anaphylaxis**.

* **Metabolic:** **hyperglycaemia**, **lactataemia** (β-driven glycolysis; not always tissue hypoperfusion), **hypokalaemia** (β₂ shift).

---

# 2) Vial strength, preparation & basic pharmacokinetics (+ disadvantages)

**Common presentations**

* **1 mg/mL** (1:1000) amp (IM use; can be diluted for infusions).

* **0.1 mg/mL** (1 mg in 10 mL; 1:10,000) prefilled syringe (IV bolus for ALS).

* Infusion mixes (ICU/OR): **4 mg in 50 mL** (80 mcg/mL) or **1 mg in 50 mL** (20 mcg/mL). Central line preferred.

**PK**

* **Onset IV:** < 1 min; **peak:** minutes; **offset:** 1–3 min after stop.

* **t½:** ~2–3 min; **metabolism:** MAO & COMT → inactive; **excretion:** renal metabolites.

**Disadvantages from PK/PD**

* Requires **continuous infusion**; narrow titration window.

* **Tachyarrhythmias**, **lactate rise**, **hyperglycaemia**.

* **Peripheral extravasation** can cause **ischaemic necrosis**.

---

# 3) Practical dosing

## A. Anaesthesia / Cardiac theatre

**Indications:** post-CPB myocardial stunning/LCOS, anaphylaxis under anaesthesia, refractory hypotension with low CO.

* **Post-CPB/LCOS infusion:** start **0.02–0.05 mcg/kg/min**, titrate q2–5 min by 0.01–0.02; typical **0.02–0.2 mcg/kg/min** (higher if refractory).

* **Rescue bolus (careful):** 10–20 **mcg** IV aliquots (0.1–0.2 mL of 1:10,000) for transient hypotension while starting infusion.

* **Math example (70 kg @ 0.1 mcg/kg/min = 7 mcg/min):** with **80 mcg/mL** → **5.25 mL/h**.

## B. ICU

**Indications:** vasodilatory shock with low CO (septic/post-CPB vasoplegia), cardiogenic shock as an inopressor when dobutamine/milrinone insufficient.

* **Start:** **0.02–0.05 mcg/kg/min**; **range:** **0.02–0.5 mcg/kg/min**.

* Combine with **norepinephrine** when SVR is very low; or with **inodilator** (dobutamine/milrinone) if afterload high and contractility poor.

## C. Life-threatening emergencies (for completeness)

* **Adult cardiac arrest (ALS):** **1 mg IV** (1:10,000) every 3–5 min cycles.

* **Anaphylaxis (adult):** **0.5 mg IM** (1:1000) mid-outer thigh; repeat q5 min PRN. Refractory → **IV infusion** (e.g., 1–4 mcg/min then titrate) under monitoring.

---

# 4) Special populations — dosing cautions

### Pregnancy

* First-line for **anaphylaxis** in pregnancy (maternal life priority); can reduce uterine blood flow at high IV doses—use **IM first** when appropriate and titrate IV carefully intra-op.

### Lactation

* Minimal oral bioavailability for infant; short t½; single/emergency doses acceptable.

### Hepatic impairment

* Widely metabolised extrahepatically; **no formal adjustment**—**titrate to effect**.

### Renal impairment

* Metabolites renally excreted but inactive; **no adjustment**. Watch perfusion and urine output.

### Obesity

* Start with **IBW/AdjBW-based** rates to avoid overshoot; titrate to haemodynamics.

### Paediatrics

* **Anaphylaxis IM:** **0.01 mg/kg** (1:1000), max **0.5 mg**.

* **Infusion:** **0.02–1 mcg/kg/min** titrated in specialist setting.

* **Cardiac arrest:** **0.01 mg/kg IV** (1:10,000 = 0.1 mL/kg).

---

# 5) Drug interactions (clinically key)

* **MAO inhibitors / TCAs / SNRIs:** **exaggerated pressor** and arrhythmic responses → start at **very low doses** or avoid.

* **Non-selective β-blockers** (e.g., propranolol): **unopposed α₁ vasoconstriction** → severe hypertension/bradycardia; bronchospasm risk persists (β₂ blocked).

* **Halogenated volatiles (esp. halothane):** myocardial sensitisation → **ventricular arrhythmias**.

* **Digoxin:** arrhythmia risk ↑.

* **Insulin/oral hypoglycaemics:** hyperglycaemia from epi may necessitate higher insulin.

* **Inhaled β₂-agonists:** additive hypokalaemia—monitor K⁺.

---

# 6) Significant complications & management

| Complication                                           | Mechanism / Features                                 | Management                                                                                                                                       |

| ------------------------------------------------------ | ---------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------ |

| **Tachyarrhythmias (AF/VT/VF)**                        | β₁ excess, esp. hypoxia/acidosis                     | Reduce/stop; correct K⁺/Mg²⁺; antiarrhythmics/defibrillate per ACLS.                                                                             |

| **Myocardial ischaemia**                               | ↑ MVO₂ + ↑ afterload                                 | Lower dose; add inodilator; ensure adequate MAP/CPP and treat pain/anaemia.                                                                      |

| **Severe hypertension / limb or mesenteric ischaemia** | α₁ vasoconstriction at high dose                     | Titrate down; reconsider target MAP; balance with inodilator.                                                                                    |

| **Lactataemia** (β-driven)                             | Accelerated glycolysis—not necessarily hypoperfusion | Interpret with context; check ScvO₂/echo; don’t chase lactate alone.                                                                             |

| **Hypokalaemia**                                       | β₂-mediated intracellular shift                      | Monitor K⁺; replace if needed.                                                                                                                   |

| **Hyperglycaemia**                                     | Glycogenolysis/gluconeogenesis                       | Adjust insulin.                                                                                                                                  |

| **Extravasation necrosis**                             | Intense local α₁ vasoconstriction                    | **Stop infusion, leave cannula**, **phentolamine 5–10 mg** in 10–15 mL saline infiltrated around site; warm compress; surgical review if severe. |

| **Pulmonary oedema**                                   | Afterload ↑ + tachycardia                            | Reduce dose; diuretics/vasodilator if appropriate; optimise ventilation.                                                                         |

---

Norepinephrine

Norepinephrine is a potent **α₁ agonist** and moderate **β₁ agonist**, producing **powerful vasoconstriction** and modest inotropy. 

It is the **first-line vasopressor** in septic, cardiogenic, and post-cardiac bypass vasodilatory shock.

Dose **0.02–0.3 mcg/kg/min**, titrated to MAP 65–75 mmHg; always via central line; treat extravasation with **phentolamine.

---

# 1) Receptor-level action → clinical effects

**Primary receptor activity:**

* **α₁ agonist (dominant):** intense arterial & venous vasoconstriction → ↑ SVR, ↑ MAP.

* **β₁ agonist (moderate):** ↑ contractility and heart rate *slightly* but offset by baroreflex-mediated bradycardia.

* **β₂ agonist (minimal):** clinically negligible.

**Net effects:**

* ↑ MAP primarily via **↑ SVR**.

* Slight ↑ myocardial contractility & CO in moderate doses (depends on preload).

* Reflex **bradycardia** common due to baroreceptor activation.

* Improves coronary and cerebral perfusion pressure.

**Clinical summary of effects:**

* **Vascular:** potent vasoconstrictor, preserves perfusion pressure.

* **Cardiac:** improves inotropy modestly; no direct chronotropy in intact baroreflex.

* **Renal/splanchnic:** vasoconstriction; at adequate MAP, **net renal perfusion improved** by higher pressure.

* **Metabolic:** can cause mild hyperglycaemia, hyperlactataemia (β-effect on metabolism).

---

# 2) Vial strength, preparation & basic pharmacokinetics (+ disadvantages)

**Formulation:**

* Standard ampoule: **4 mg/4 mL (1 mg/mL)**.

* Common ICU dilution: **4 mg in 50 mL** → **80 mcg/mL** (1 mL/h = 1.33 mcg/min).

  * Alternative: **8 mg/50 mL** (160 mcg/mL) for central use.

**Pharmacokinetics:**

* **Onset:** <1 min.

* **Duration:** 1–2 min (terminated rapidly by reuptake/metabolism).

* **Metabolism:** MAO & COMT → inactive metabolites.

* **Half-life:** ~2.5 min.

* **Elimination:** renal excretion of metabolites.

**Disadvantages:**

* **Requires continuous infusion**, short half-life.

* **Peripheral extravasation → severe tissue necrosis.**

* Excessive vasoconstriction → impaired peripheral, mesenteric, or renal flow if MAP overshoot.

* **Arrhythmia risk** lower than dopamine, but possible with high doses.

---

# 3) Practical dosing

## A. Anaesthesia / Post–cardiac bypass

**Indications:** hypotension due to vasodilation, vasoplegia, or low SVR after CPB, sepsis, or anaesthetic-induced vasodilation.

* **Starting dose:** **0.02–0.05 mcg/kg/min**.

* **Titrate up:** by 0.01–0.02 mcg/kg/min increments.

* **Typical range:** **0.02–0.3 mcg/kg/min** (occasionally higher in refractory vasoplegia).

* **Usual ICU practice:** aim for **MAP 65–75 mmHg** (individualised).

**Preparation examples (for 70 kg):**

* 70 × 0.1 mcg/kg/min = 7 mcg/min.

  Using 80 mcg/mL solution → rate = **5.25 mL/h.**

**Peripheral use (if emergency):**

* Use **max 15–20 min** only through **large antecubital vein**; monitor closely; change to central line ASAP.

---

# 4) Special populations — dosing cautions

### Pregnancy

* Used for **maternal hypotension** during spinal/epidural anaesthesia; maintains **better fetal acid–base status** than phenylephrine (lower reflex bradycardia).

* Crosses placenta minimally; **safe in obstetric anaesthesia** when titrated carefully.

### Lactation

* Short t½ and poor oral absorption → minimal transfer risk.

### Hepatic impairment

* Metabolised widely (not dependent on hepatic clearance). No dose adjustment required; **titrate to effect**.

### Renal impairment

* Metabolite excretion renal but inactive; **safe**.

* Improves renal perfusion indirectly via better MAP.

### Obesity

* Dose by **ideal body weight** to avoid excessive pressor effect.

### Paediatrics

* **Starting:** 0.05 mcg/kg/min; titrate to 1–2 mcg/kg/min if required (specialist monitoring).

---

# 5) Drug interactions (clinically key)

* **MAOIs:** marked pressor response → start at **1/10th** normal dose or avoid.

* **TCAs / SNRIs:** exaggerated BP response.

* **Halogenated volatiles (esp. halothane):** myocardial sensitisation → **ventricular arrhythmia risk.**

* **β-blockers:** may cause unopposed α-stimulation → **severe hypertension/bradycardia**.

* **Ergot alkaloids, oxytocin:** additive vasoconstriction.

* **Phosphodiesterase inhibitors (milrinone):** synergistic—useful combination for inodilator + vasopressor balance.

* **General anaesthetics / propofol:** counteract vasodilation; titrate slowly.

---

# 6) Significant complications & management

| Complication                              | Mechanism / Features                       | Management                                                                                                                                     |

| ----------------------------------------- | ------------------------------------------ | ---------------------------------------------------------------------------------------------------------------------------------------------- |

| **Peripheral extravasation necrosis**     | α₁ vasoconstriction → ischaemia            | Stop infusion, leave cannula, **phentolamine 5–10 mg in 10–15 mL saline** infiltrated around site; warm compress; surgical review if necrosis. |

| **Digital/mesenteric ischaemia**          | Excess vasoconstriction                    | Lower dose, reassess MAP goal, switch/add inodilator.                                                                                          |

| **Arrhythmia (AF/VT)**                    | β₁ effect, usually in high dose or hypoxia | Correct electrolytes, reduce dose; antiarrhythmics as indicated.                                                                               |

| **Reflex bradycardia**                    | Baroreceptor response                      | Often mild; if MAP adequate, observe. Severe → **atropine/glycopyrrolate** if symptomatic.                                                     |

| **Metabolic acidosis / hyperlactataemia** | From high β-stimulation (non-hypoxic)      | Usually benign; evaluate perfusion if severe.                                                                                                  |

---