Sodium Nitroprusside Pharmacology

Quick Answer

Sodium nitroprusside (SNP) is a potent, rapid-acting, direct-acting vasodilator that produces arteriolar and venous dilation through non-specific release of nitric oxide (NO). It is a complex inorganic compound (disodium pentacyanonitrosylferrate(2-) dihydrate) that spontaneously degrades in solution to release NO, which activates guanylate cyclase in vascular smooth muscle, increasing cGMP and causing profound vasodilation.

The drug's pharmacological profile is characterized by immediate onset (within seconds), rapid offset (1-3 minutes after discontinuation), and profound potency, making it ideal for precise titration of blood pressure in controlled settings. Sodium nitroprusside reduces both preload (venous dilation) and afterload (arteriolar dilation), with balanced effects on both vascular beds.

Clinical applications include controlled hypotension to reduce bleeding during surgery, management of hypertensive crises, afterload reduction in acute heart failure, and intraoperative blood pressure control. The standard dosing is 0.5-10 mcg/kg/min via continuous infusion with invasive arterial pressure monitoring mandatory.

The major limitation is the risk of cyanide toxicity, which occurs when the rate of cyanide liberation from nitroprusside exceeds the body's detoxification capacity. Each molecule of nitroprusside contains five cyanide groups, which are slowly released. Toxicity manifests with metabolic acidosis, tachyphylaxis (resistance to further hypotensive effect), elevated mixed venous oxygen saturation, and altered consciousness. Cyanide is detoxified to thiocyanate by rhodanese in the liver using thiosulfate as a sulfur donor; thiocyanate is then renally eliminated. Risk factors include high-dose prolonged infusion (>2 mcg/kg/min for >24-48 hours), hepatic or renal impairment, and vitamin B12 deficiency. Prevention strategies include limiting duration and dose, coadministration of thiosulfate, and monitoring for signs of toxicity. [1-22]

Pharmacology Overview

Drug Classification and History

Sodium nitroprusside is an inorganic complex salt classified as a direct-acting, non-selective vasodilator. It was first synthesized in 1850 but not used clinically until 1929 when it was employed for blood pressure control. Johnson first reported its use in deliberate hypotension in 1955, and it became widely adopted for controlled hypotension in anaesthesia in the 1970s.

The drug has a unique chemical structure among anaesthetic drugs: an iron atom in the ferrous oxidation state coordinated to five cyanide ligands and one nitrosyl group (NO+). This structure is responsible for both its pharmacological activity (NO release) and its toxicity (cyanide release).

Primary clinical applications include:

1. Controlled hypotension: Reduce blood pressure to minimize surgical bleeding (orthopaedic spine surgery, ENT surgery)
2. Hypertensive crises: Rapid reduction of dangerously elevated blood pressure
3. Acute heart failure: Afterload reduction to improve cardiac output
4. Aortic dissection: Control blood pressure while preparing for surgery
5. Intraoperative hypertension: Immediate blood pressure control during general anaesthesia

The drug is highly effective but requires careful monitoring due to toxicity risks. Its use has declined somewhat with the availability of alternative agents (esmolol, nicardipine, clevidipine) that do not carry cyanide toxicity risk, but it remains an important drug for specific indications. [23-35]

Chemical Structure and Physicochemical Properties

Sodium nitroprusside has the molecular formula Na2[Fe(CN)5NO]·2H2O and molecular weight of 297.9 g/mol. The chemical name is disodium pentacyanonitrosylferrate(2-) dihydrate.

Structural Features: The molecule consists of:

• Central ferrous iron (Fe2+) atom
• Five cyanide (CN-) ligands coordinated to the iron
• One nitrosyl (NO+) group coordinated to the iron
• Two sodium cations for charge neutrality
• Two water molecules (hydrate form)

Key Physicochemical Properties:

Light Sensitivity: Sodium nitroprusside is highly sensitive to light, which causes photochemical degradation:

• Degrades to form ferrocyanide, cyanide, and other breakdown products
• Solution turns blue-green when degraded
• Must be protected from light using foil wrapping or amber tubing
• Should be prepared fresh and used within 4 hours

Chemical Instability: The nitroprusside ion is inherently unstable and slowly releases cyanide even without metabolism:

• Each molecule contains 5 cyanide groups
• One mole of nitroprusside releases 5 moles of cyanide theoretically
• Rate of cyanide release increases with increasing pH
• Rate increases with higher temperatures
• Storage requires protection from light and heat

Incompatibility:

• Incompatible with alkaline solutions (forms precipitate)
• Incompatible with many drugs (check compatibility before mixing)
• Use dedicated IV line or compatible carrier fluid [36-45]

Comparison with Other Vasodilators

Clinical Implications:

1. Nitroprusside advantage: Immediate onset/offset, arterial and venous dilation, excellent titration
2. Nitroprusside disadvantage: Cyanide toxicity risk
3. Alternative agents: Clevidipine and nicardipine have largely replaced nitroprusside for many indications due to safety profile
4. Nitroglycerine: Preferred for coronary ischemia (coronary vasodilation), less systemic hypotension
5. Hydralazine: Not suitable for rapid titration; used for chronic hypertension [46-55]

Mechanism of Action

Nitric Oxide Release and Vasodilation

Sodium nitroprusside acts as a direct nitric oxide (NO) donor. The mechanism involves spontaneous chemical degradation and interaction with red blood cells and vascular endothelium:

1. Spontaneous NO Release:

• Nitroprusside ion [Fe(CN)5NO]2- spontaneously releases nitric oxide (NO) in solution
• NO diffuses into vascular smooth muscle cells
• Release is non-enzymatic and immediate

2. Red Blood Cell Interaction (Primary Mechanism):

• When nitroprusside enters red blood cells:
  • Interacts with oxyhemoglobin
  • Transfers electron to nitroso group, releasing NO
  • Five cyanide groups also released (toxicity mechanism)
• Released NO diffuses out of RBCs to vascular smooth muscle

3. Vascular Smooth Muscle Effects:

• NO enters vascular smooth muscle cells
• Binds to heme moiety of soluble guanylate cyclase (sGC)
• Activates sGC → converts GTP to cyclic guanosine monophosphate (cGMP)
• cGMP activates protein kinase G (PKG)
• PKG phosphorylates proteins leading to:
  • Sequestration of cytosolic calcium into sarcoplasmic reticulum
  • Decreased calcium sensitivity of contractile proteins
  • Opening of potassium channels → hyperpolarization
• Net effect: Smooth muscle relaxation → vasodilation

Molecular Pathway:

SNP → NO release → sGC activation → cGMP↑ → PKG activation → 
Ca2+ sequestration + K+ channel opening → 
Vascular smooth muscle relaxation → Vasodilation

Site of Action:

• Arterioles (resistance vessels): Reduced systemic vascular resistance (afterload)
• Venules (capacitance vessels): Reduced venous return (preload)
• Balanced effect on both arterial and venous systems (distinguishes from nitroglycerine which is primarily venous)

Comparison with Endogenous NO:

• Nitroprusside releases NO non-specifically (not endothelium-dependent)
• Affects all vascular beds (no selectivity)
• No tachyphylaxis (unlike nitroglycerine which requires functional enzymes)
• No direct effect on heart, brain, or other tissues (indirect effects via hemodynamics) [56-70]

Cyanide Liberation and Toxicity

The five cyanide ligands in nitroprusside are the source of its toxicity:

Mechanism of Cyanide Release:

1. Spontaneous decomposition: Slow release of cyanide from the molecule in solution
2. Metabolic release: When SNP interacts with red blood cells and tissues, cyanide is liberated
3. Rate of release: Approximately 1 cyanide ion per nitroprusside molecule per minute under normal conditions
4. Dose-dependent: Higher infusion rates → more cyanide released

Cyanide Pharmacokinetics:

• Volume of distribution: Rapid distribution to all tissues
• Mechanism of toxicity: Binds to cytochrome c oxidase (mitochondrial enzyme)
• Effect: Blocks electron transport chain → cellular hypoxia (histotoxic hypoxia)
• Metabolism: Detoxified to thiocyanate (less toxic)
• Elimination: Thiocyanate eliminated renally (half-life 2-4 days)

Detoxification Pathway:

Cyanide + Thiosulfate → Thiocyanate + Sulfite
        ↓ Rhodanese (liver)
        Thiocyanate (excreted in urine)

Thiosulfate:

• Required as sulfur donor for rhodanese reaction
• Endogenous stores limited (can be exhausted with high dose SNP)
• Can be supplemented exogenously to enhance cyanide detoxification

Vitamin B12 (Hydroxocobalamin):

• Binds cyanide to form cyanocobalamin (non-toxic)
• Alternative/ adjunctive treatment for cyanide toxicity
• Precursor form (hydroxocobalamin) used as antidote

Thiocyanate Toxicity:

• Less toxic than cyanide
• Occurs with prolonged therapy or renal failure (accumulation)
• Symptoms: Weakness, nausea, tinnitus, blurred vision, delirium
• Eliminated by hemodialysis

Risk Factors for Cyanide Toxicity:

1. High dose (>2 mcg/kg/min for >24-48 hours)
2. Prolonged infusion (>24-48 hours)
3. Hepatic impairment (reduced rhodanese activity)
4. Renal impairment (reduced thiocyanate elimination)
5. Depleted thiosulfate stores
6. Vitamin B12 deficiency
7. Leber hereditary optic neuropathy (LHON)

Clinical Monitoring for Toxicity:

1. Metabolic acidosis: Lactic acidosis from cellular hypoxia (most sensitive indicator)
2. Tachyphylaxis: Loss of hypotensive effect despite increasing dose
3. Elevated mixed venous oxygen saturation: Tissue unable to extract oxygen
4. Altered consciousness: Headache, confusion, seizures, coma
5. Serum lactate elevation: >2 mmol/L suggests toxicity

Prevention Strategies:

1. Limit maximum dose (≤10 mcg/kg/min, preferably ≤2 mcg/kg/min)
2. Limit duration (<24 hours if possible)
3. Monitor acid-base status regularly
4. Consider coadministration of thiosulfate (1:10 ratio with SNP)
5. Ensure adequate oxygenation (100% FiO2 increases cyanide elimination)
6. Avoid in hepatic/renal impairment
7. Switch to alternative agents when prolonged therapy needed

Treatment of Cyanide Toxicity:

1. Discontinue nitroprusside immediately
2. 100% oxygen (enhances cyanide elimination)
3. Hydroxocobalamin (Cyanokit): 5g IV over 15 minutes (adult dose)
4. Sodium thiosulfate: 12.5g IV (provides sulfur for detoxification)
5. Sodium nitrite (if no hydroxocobalamin available): Induces methemoglobin which binds cyanide
6. Supportive care: Ventilation, circulation, treatment of acidosis
7. Hemodialysis: For severe toxicity or thiocyanate accumulation [71-95]

Pharmacokinetic Principles

Absorption and Onset

Sodium nitroprusside is administered only via intravenous route:

Intravenous Administration:

• Onset: Immediate (<30 seconds)
• Mechanism: Direct entry into bloodstream, immediate NO release
• Time to peak effect: 1-2 minutes at steady-state infusion
• Factors affecting onset: Cardiac output (delivery to vascular beds), volume of distribution

No Other Routes:

• Oral: Not absorbed (would cause severe toxicity)
• IM: Not used (erratic absorption, local toxicity)
• Subcutaneous: Not used
• Topical: Not used

Distribution

Distribution Characteristics:

• Rapid distribution to all tissues due to water solubility and small molecular size
• Red blood cells are the primary site of NO and cyanide liberation
• Does not accumulate in fat (hydrophilic)
• Equilibrates rapidly with vascular smooth muscle

Metabolism

Sodium nitroprusside undergoes unique metabolism involving both therapeutic (NO release) and toxic (cyanide release) pathways:

Primary Metabolic Pathways:

1. Nitric Oxide Release (Therapeutic):

• Rate: Immediate and continuous
• Location: Red blood cells primarily
• Product: NO (active vasodilator)
• Mechanism: Interaction with oxyhemoglobin

2. Cyanide Liberation (Toxic):

• Rate: Approximately 1 cyanide ion per nitroprusside molecule per minute
• Location: Red blood cells, plasma, tissues
• Product: Free cyanide (CN-)
• Mechanism: Degradation of the complex

3. Cyanide Detoxification:

• Primary pathway: Rhodanese reaction in liver

  • Cyanide + Thiosulfate → Thiocyanate
  • Requires thiosulfate as sulfur donor
  • Rate-limiting step in detoxification

• Secondary pathway: Hydroxocobalamin binding

  • Cyanide + Hydroxocobalamin → Cyanocobalamin (B12)
  • Occurs in blood and tissues
  • Saturable at high cyanide levels

4. Thiocyanate Elimination:

• Primary elimination: Renal excretion (glomerular filtration)
• Elimination half-life: 2-4 days
• Toxicity: Accumulates in renal failure

Metabolism Summary:

SNP infusion
     ↓
NO release (vasodilation - therapeutic)
     ↓
Cyanide release (toxic)
     ↓
┌─────────────────┬──────────────────┐
│ 1. Rhodanese    │ 2. Hydroxoco-    │
│    (liver)      │    balamin       │
│ CN- + S2O3²-    │ CN- + OH-B12     │
│    ↓            │    ↓             │
│ SCN- + SO3²-    │ CN-B12           │
└─────────────────┴──────────────────┘
     ↓
Thiocyanate → Renal elimination (slow)

Factors Affecting Metabolism:

1. Hepatic function: Impaired rhodanese activity in liver disease
2. Renal function: Impaired thiocyanate elimination in renal failure
3. Thiosulfate availability: Depleted stores with high-dose SNP
4. Vitamin B12 status: Affects alternative detoxification pathway
5. Oxygenation: 100% O2 enhances cyanide elimination
6. Duration and dose: Cumulative cyanide load

Half-life:

• Nitroprusside effect: 1-3 minutes (redistribution and metabolism)
• Cyanide: Hours (depending on detoxification capacity)
• Thiocyanate: 2-4 days (rate-limiting step) [96-110]

Elimination

Nitroprusside Elimination:

• Primary: Metabolic conversion (not renal/hepatic clearance in traditional sense)
• Duration of action: 1-3 minutes after discontinuation
• Factors affecting offset: Redistribution, metabolism to NO and cyanide

Cyanide Elimination:

• Pathway: Conversion to thiocyanate
• Rate: Limited by rhodanese activity and thiosulfate availability
• Accumulation: Occurs when production exceeds detoxification

Thiocyanate Elimination:

• Primary: Renal excretion (glomerular filtration)
• Half-life: 2-4 days
• Accumulation: In renal failure (dialysis required)

Clinical Implications:

1. Rapid offset: Effect stops within minutes of discontinuation
2. Cumulative toxicity: Cyanide can accumulate despite rapid vasodilator offset
3. Renal failure: Thiocyanate toxicity risk with prolonged use
4. Hepatic failure: Impaired cyanide detoxification

Kinetic Summary

Titration Characteristics:

• Excellent titration due to rapid onset/offset
• Can increase or decrease BP within minutes
• Ideal for precise blood pressure control
• Requires continuous infusion (no intermittent boluses) [111-120]

Pharmacodynamics: Systemic Effects

Cardiovascular Effects

Blood Pressure: Sodium nitroprusside produces profound, dose-dependent hypotension:

• Mechanism: Combined reduction of preload (venous dilation) and afterload (arteriolar dilation)
• Onset: Immediate (<30 seconds)
• Offset: 1-3 minutes after discontinuation
• Dose-response: Linear relationship between infusion rate and blood pressure reduction
• Titration: Can adjust BP to precise target within narrow range

Heart Rate:

• Reflex tachycardia: Baroreceptor-mediated increase in heart rate (10-20 bpm typical)
• Mechanism: Hypotension triggers sympathetic activation
• Clinical significance: Can increase myocardial oxygen demand; may require beta-blocker
• Prevention/Treatment: Coadministration of beta-blocker or clonidine

Cardiac Output:

• Variable effect: Depends on preloading conditions and contractility
• Normal heart: Usually maintained or slightly increased (afterload reduction benefits)
• Impaired heart: May decrease (excessive preload reduction)
• Goal: Optimize balance between afterload reduction and preload maintenance

Systemic Vascular Resistance:

• Marked reduction: 30-50% decrease typical at therapeutic doses
• Balanced: Affects both resistance and capacitance vessels
• Site: Arterioles primarily, but veins also dilated

Pulmonary Vascular Resistance:

• Reduction: Decreases PVR through pulmonary vasodilation
• Benefit: In right heart failure, pulmonary hypertension
• Caution: May worsen V/Q mismatch (inhibition of hypoxic pulmonary vasoconstriction)

Coronary Circulation:

• Dilates coronary arteries: Direct effect on coronary vasculature
• Coronary steal: Possible (dilation of normal vessels shunts blood from stenotic areas)
• Net effect: Generally improves coronary perfusion if systemic BP maintained
• Concern: Reflex tachycardia increases oxygen demand

Central Venous Pressure:

• Reduction: 30-50% decrease in CVP due to venous dilation
• Effect: Reduced preload to right ventricle
• Clinical significance: May compromise cardiac output in preload-dependent patients

Myocardial Oxygen Balance:

• Supply: Improved (coronary dilation, reduced afterload)
• Demand: Increased (reflex tachycardia)
• Net effect: Depends on patient factors; may require beta-blocker to control heart rate

Comparison with Nitroglycerine:

• Nitroprusside: Arterial = Venous dilation; profound hypotension; no coronary steal concern
• Nitroglycerine: Venous > Arterial; less hypotension; coronary steal possible
• Selection: Nitroprusside for afterload reduction; nitroglycerine for coronary ischemia [121-140]

Central Nervous System Effects

Cerebral Blood Flow:

• Increases CBF: Cerebral vasodilation
• Increases ICP: Can raise intracranial pressure
• Mechanism: Direct cerebral vasodilation (similar to other vessels)
• Contraindication: In patients with increased ICP (risk of brain herniation)
• Clinical consideration: Ensure cerebral perfusion pressure maintained (MAP >60-70 mmHg)

Intracranial Pressure:

• Elevation: Dose-dependent increase in ICP
• Mechanism: Vasodilation increases cerebral blood volume
• Risk: Brain herniation in patients with mass lesions or edema
• Contraindicated: In neurosurgery patients with elevated ICP

Cerebral Metabolism:

• Minimal direct effect on cerebral metabolic rate
• Indirect effects via blood pressure changes

Neurological Monitoring:

• Assess consciousness level (indicator of cerebral perfusion)
• Monitor for signs of cyanide toxicity (altered mental status)
• EEG changes if profound hypotension [141-150]

Respiratory Effects

Ventilation:

• Minimal direct effect on respiratory drive
• Indirect effects via changes in cerebral blood flow

Pulmonary Circulation:

• Reduces pulmonary vascular resistance
• May reduce hypoxic pulmonary vasoconstriction
• Potential to worsen V/Q mismatch and hypoxemia
• Monitor oxygenation during use

Airway Resistance:

• No significant bronchodilator or bronchoconstrictor effect
• Safe in asthmatic patients [151-155]

Renal Effects

Renal Blood Flow:

• Autoregulation lost: Below MAP of ~80 mmHg, renal blood flow becomes pressure-dependent
• Risk: Acute kidney injury if excessive hypotension
• Monitoring: Urine output, creatinine
• Target: Maintain MAP >65-70 mmHg to preserve renal perfusion

Sodium Excretion:

• Minimal effect on renal tubular function
• Can cause diuresis due to reduced renal perfusion (prerenal)

Thiocyanate Elimination:

• Kidney eliminates thiocyanate (end-product of cyanide metabolism)
• Renal impairment causes thiocyanate accumulation
• Monitor renal function with prolonged use [156-160]

Metabolic and Biochemical Effects

Oxygen Extraction:

• Elevated mixed venous oxygen saturation: Hallmark of cyanide toxicity
• Normal: SvO2 reflects tissue oxygen extraction
• Cyanide toxicity: SvO2 >70-80% (tissues cannot extract oxygen)
• Monitoring: Mixed venous oxygen saturation if pulmonary artery catheter in place

Acid-Base Status:

• Metabolic acidosis: Lactic acidosis from cellular hypoxia (cyanide toxicity)
• Monitor: Arterial blood gas, serum lactate
• Early indicator: Rising lactate may precede other signs of toxicity

Cyanide and Thiocyanate Levels:

• Cyanide: Can be measured but levels correlate poorly with toxicity
• Thiocyanate: >100 mcg/mL associated with toxicity
• Clinical utility: Limited; clinical assessment more important

Methemoglobin:

• Not produced by nitroprusside (unlike nitroglycerine at very high doses)
• Hydroxocobalamin treatment can cause red urine (harmless) [161-170]

Clinical Pharmacology

Clinical Indications and Dosing

1. Controlled Hypotension (Deliberate Hypotension)

Indications:

• Major spine surgery (scoliosis, spinal fusion)
• Major head and neck surgery
• Intracranial surgery (when ICP not elevated)
• Orthopaedic procedures (hip arthroplasty, major spine)
• Any surgery where reduced bleeding improves surgical field

Rationale:

• Reduced MAP → reduced bleeding from capillaries and small vessels
• Improved surgical field visibility
• Reduced transfusion requirements
• Shorter operative time (better visualization)

Target Blood Pressure:

• Mean arterial pressure (MAP): 50-70 mmHg (patient-dependent)
• Systolic BP: 80-100 mmHg
• Not below 50 mmHg (risk of organ ischemia)
• Maintain cerebral perfusion pressure (CPP = MAP - ICP)

Dosing:

• Initial: 0.5 mcg/kg/min
• Titrate: Increase by 0.5 mcg/kg/min every 3-5 minutes
• Typical range: 0.5-10 mcg/kg/min (average 1-3 mcg/kg/min)
• Maximum: 10 mcg/kg/min (preferably ≤2 mcg/kg/min for prolonged use)
• Duration: Preferably <4-6 hours (risk of toxicity increases with time)

Monitoring Requirements:

• Arterial line: Mandatory for continuous BP monitoring
• Central line: Often used for CVP monitoring and drug administration
• Pulse oximetry: Continuous
• ECG: Continuous
• Urine output: Hourly (target >0.5 mL/kg/hr)
• ABG: Regular (monitor for acidosis)
• Temperature: Avoid hypothermia

Adjuncts:

• Position: Head-up tilt reduces cerebral venous pressure
• Beta-blocker: Control reflex tachycardia (esmolol, labetalol)
• Anaesthesia: Ensure adequate depth
• Fluid loading: Optimize preload before starting

Limitations and Risks:

• Risk of cyanide toxicity
• Risk of organ ischemia (brain, heart, kidneys, spinal cord)
• Contraindicated in ischemic heart disease, cerebrovascular disease, renal impairment
• Requires intensive monitoring

Alternative Agents:

• Clevidipine: Preferred by many (no cyanide toxicity)
• Esmolol: For control of tachycardia
• Nitroglycerine: If venous pooling desired
• Trimethaphan: Rarely used today
• High-dose volatile agents: Isoflurane, desflurane

Postoperative Considerations:

• Gradual return to normal BP (avoid rebound hypertension)
• Monitor for delayed toxicity
• Assess for end-organ damage [171-195]

2. Hypertensive Crises

Indications:

• Malignant hypertension with end-organ damage
• Hypertensive encephalopathy
• Acute aortic dissection
• Acute pulmonary edema with hypertension
• Perioperative hypertension
• Pheochromocytoma crisis

Rationale:

• Immediate BP control
• Short-acting (can stop if overshoot)
• Precise titration

Contraindications in Hypertensive Crisis:

• Cerebral ischemia: If stroke in evolution (risk of worsening ischemia)
• Compensatory hypertension: Cushing response (head injury), aortic coarctation

Dosing:

• Same as controlled hypotension (0.5-10 mcg/kg/min)
• Target: 10-20% reduction in first hour, not >25% in first hour
• Avoid precipitous drops (risk of cerebral/coronary ischemia)

Alternative Agents for Hypertensive Crisis:

• Nicardipine: Preferred by many (no cyanide risk)
• Clevidipine: Ultra-short acting
• Esmolol: If tachycardia component
• Hydralazine: Less titratable, longer acting
• Enalaprilat: ACE inhibitor (slower onset)

Duration:

• Transition to oral agents as soon as feasible
• Avoid prolonged SNP use due to toxicity [196-210]

3. Acute Heart Failure / Afterload Reduction

Indications:

• Acute decompensated heart failure with preserved blood pressure
• Acute mitral regurgitation
• Acute ventricular septal defect
• Severe hypertension with flash pulmonary edema

Rationale:

• Reduces afterload (systemic vascular resistance)
• Improves cardiac output (reduced impedance to ventricular ejection)
• Reduces myocardial oxygen demand (reduced wall stress)

Caution:

• Excessive preload reduction can worsen cardiac output
• Maintain adequate preload (monitor CVP)
• Reflex tachycardia increases oxygen demand

Alternative Agents:

• Nitroglycerine: If preload reduction also needed
• Milrinone: Inotrope + vasodilator
• Dobutamine: If inotropy needed
• ACE inhibitors: Captopril, enalaprilat

Monitoring:

• Hemodynamics (arterial line, possibly PAC)
• Echocardiography to assess cardiac function
• Clinical endpoints (perfusion, urine output) [211-220]

4. Intraoperative Blood Pressure Control

Indications:

• Hypertensive episodes during surgery
• Prevention of hypertensive responses (laryngoscopy, surgical stimulation)
• Maintenance of target BP range

Advantages:

• Immediate onset
• Rapid offset
• Precise titration
• Can stop quickly if hypotension occurs

Disadvantages:

• Cyanide toxicity risk
• Reflex tachycardia
• Potential for excessive hypotension
• Requires arterial line

Use:

• Boluses not appropriate (profound hypotension risk)
• Low-dose infusion titrated to effect
• Consider alternatives (esmolol, labetalol) for less critical situations [221-230]

Contraindications

Drug Interactions

Special Populations

Pediatric Patients

Limited Data:

• Used for controlled hypotension in paediatric spine surgery
• Cyanide toxicity reports in children (higher risk per kg)
• Lower maximum recommended doses
• Extreme caution with prolonged use

Dosing:

• 0.5-5 mcg/kg/min (lower range than adults)
• Maximum 4-6 mcg/kg/min
• Preferably <2 mcg/kg/min
• Monitor for toxicity meticulously

Considerations:

• Higher risk of cyanide toxicity (higher dose per kg often needed)
• Ensure adequate thiosulfate stores
• Consider alternatives (clevidipine, esmolol) [231-240]

Pregnancy

Contraindicated:

• Cyanide crosses placenta
• Fetal cyanide toxicity risk
• Alternative agents preferred (hydralazine, labetalol, nicardipine)

Use only if:

• Life-threatening maternal condition
• No alternatives available
• Short-term use only
• Fetal monitoring essential [241-245]

Elderly Patients

Considerations:

• Impaired cerebral autoregulation
• Increased sensitivity to hypotension
• Risk of cerebral/coronary ischemia
• Lower starting doses
• Slower titration
• Consider alternatives [246-250]

Adverse Effects and Complications

Cyanide Toxicity

Pathophysiology:

• Cyanide binds to cytochrome c oxidase (mitochondrial enzyme)
• Blocks electron transport chain
• Cellular hypoxia despite adequate oxygen delivery (histotoxic hypoxia)
• Lactic acidosis from anaerobic metabolism

Clinical Features:

Diagnosis:

• Clinical: Most important; do not wait for lab confirmation
• Metabolic acidosis with elevated lactate: Most sensitive early indicator
• Tachyphylaxis: Loss of hypotensive effect despite escalating dose
• Elevated mixed venous oxygen saturation: >70-80% indicates tissue inability to extract oxygen
• Altered mental status: Late sign
• Serum cyanide level: >1 mcg/mL suggests toxicity (not always immediately available)
• Blood gas: Metabolic acidosis with normal or high oxygen saturation

Risk Factors:

1. Dose >2 mcg/kg/min for >24-48 hours
2. Duration >24-48 hours
3. Hepatic impairment
4. Renal impairment
5. Depleted thiosulfate stores (malnutrition)
6. Vitamin B12 deficiency
7. Leber hereditary optic neuropathy
8. High-dose short-term infusions (>10 mcg/kg/min)

Prevention:

1. Limit maximum dose (≤10 mcg/kg/min, preferably ≤2 mcg/kg/min)
2. Limit duration (<4-6 hours if possible)
3. Monitor acid-base status every 4-6 hours with prolonged use
4. Coadminister sodium thiosulfate (provides sulfur for detoxification)
   • Ratio: 1:10 with nitroprusside dose
   • Example: 10 mg thiosulfate per 1 mg nitroprusside
5. Ensure 100% oxygen (enhances cyanide elimination)
6. Monitor serum lactate
7. Switch to alternative agents for prolonged therapy

Treatment:

Immediate (ABC):

1. Discontinue nitroprusside immediately
2. 100% oxygen (hyperbaric oxygen if available)
3. Supportive care: Ventilation, circulation, correct acidosis (sodium bicarbonate if pH <7.2)

Antidotes (in order of preference):

1. Hydroxocobalamin (Cyanokit) - First Line:

• Dose: 5g IV over 15 minutes (adult)
• Mechanism: Binds cyanide to form cyanocobalamin (non-toxic vitamin B12)
• Advantages: Rapid, effective, safe
• Side effects: Red discoloration of urine, skin, mucous membranes (harmless)
• Can repeat 5g if needed (total 10g)

2. Sodium Thiosulfate:

• Dose: 12.5g IV (150 mg/kg or 0.5 g/kg)
• Mechanism: Provides sulfur for rhodanese to convert cyanide to thiocyanate
• Advantages: Readily available, inexpensive
• Limitations: Slow onset (requires time for conversion)
• Can give concurrently with hydroxocobalamin

3. Sodium Nitrite (if hydroxocobalamin unavailable):

• Dose: 300mg IV (10 mg/kg) over 5-10 minutes
• Mechanism: Induces methemoglobin, which binds cyanide
• Caution: Causes hypotension and methemoglobinemia; avoid in smoke inhalation victims (already have CO and cyanide)
• Not preferred in anaesthetic setting

4. 100% Oxygen + Supportive Care:

• Enhances endogenous detoxification
• Essential adjunct to antidotes

Advanced Support:

• Hemodialysis: Removes thiocyanate (not cyanide directly)
• Hyperbaric oxygen: Increases oxygen delivery to tissues
• Cardiovascular support: Vasopressors, inotropes

Monitoring During Treatment:

• Serial ABGs and lactate levels
• Hemodynamics
• Mental status
• Cyanide levels (if available)

Recovery:

• Hours to days depending on severity
• May have neurological sequelae if severe
• Delayed effects possible [251-280]

Thiocyanate Toxicity

Pathophysiology:

• Thiocyanate (SCN-) is the end-product of cyanide detoxification
• Eliminated by kidneys (half-life 2-4 days)
• Accumulates in renal failure or prolonged therapy

Clinical Features:

• Weakness, fatigue
• Nausea, vomiting
• Tinnitus
• Blurred vision
• Delirium, psychosis
• Seizures (rare)
• Thyroid dysfunction (interferes with iodine uptake)

Diagnosis:

• Serum thiocyanate >100 mcg/mL (toxic level)
• Clinical context (prolonged SNP use + renal impairment)

Treatment:

• Discontinue nitroprusside
• Hemodialysis removes thiocyanate effectively
• Supportive care

Prevention:

• Monitor renal function
• Avoid prolonged use in renal impairment
• Consider alternative agents

Other Adverse Effects

Australian/NZ Specific Considerations

TGA-Approved Formulations

Sodium nitroprusside is TGA-approved in Australia in the following formulation:

Preparation:

• Reconstitute 50 mg powder with 5 mL 5% dextrose (10 mg/mL)
• Further dilute in 250-1000 mL 5% dextrose for infusion
• Final concentration typically 100-200 mcg/mL
• Protect from light with foil wrapping
• Use within 4 hours of preparation

Storage:

• Store intact vials at room temperature (protect from light)
• Do not refrigerate reconstituted solution
• Discard if discoloration (blue, green, red) observed

PBS and Regulatory Status

Availability:

• Available in Australian hospitals
• Not PBS-listed (hospital use only)
• Cost: Moderate (requires preparation)
• Restricted to ICU, operating theatre, emergency department use

Use Trends:

• Declining use due to safety concerns
• Clevidipine and nicardipine increasingly preferred
• Reserved for specific indications where rapid titration essential
• Requires senior medical staff approval in many institutions

ANZCA Guidelines

ANZCA Professional Documents:

• No specific guideline on nitroprusside
• Covered in general pharmacology curriculum
• Safety warnings emphasized in training

ANZCA Primary Examination: Nitroprusside is high-yield for examinations:

• Mechanism of action (NO release)
• Cyanide toxicity (mechanism, signs, treatment)
• Clinical applications (controlled hypotension, hypertensive crisis)
• Contraindications (compensatory hypertension, B12 deficiency)
• Comparison with other vasodilators

Current Practice in Australia/NZ:

• Use declining in favor of clevidipine and nicardipine
• Still used for controlled hypotension in spine surgery
• Requires intensive monitoring
• Cyanide toxicity awareness mandatory
• Alternative agents preferred for most indications [281-295]

Environmental and Occupational Considerations

Waste Disposal:

• Unused solution: Dispose as cytotoxic waste (contains cyanide)
• Do not pour down drain untreated
• Deactivate with sodium hypochlorite (bleach) before disposal

Occupational Safety:

• Cyanide release during preparation and administration
• Use in well-ventilated areas
• Avoid inhalation of powder or aerosols
• PPE when preparing (gloves, eye protection)

Indigenous Health Considerations

Aboriginal and Torres Strait Islander Considerations

Health Context: Aboriginal and Torres Strait Islander Australians have higher rates of chronic diseases that may impact nitroprusside use:

Chronic Kidney Disease:

• 3-4 times higher rates of CKD
• Thiocyanate accumulation risk with prolonged use
• Prefer alternative agents (clevidipine) if renal impairment
• Monitor renal function carefully

Cardiovascular Disease:

• Higher rates of ischaemic heart disease
• Reflex tachycardia may precipitate ischemia
• Beta-blocker coadministration may be needed
• Consider alternatives that don't cause tachycardia

Nutritional Status:

• Risk of malnutrition and vitamin deficiencies
• Ensure adequate thiosulfate stores (sulfur-containing amino acids)
• B12 status may be compromised

Access and Monitoring:

• Remote facilities may have limited monitoring capabilities
• Arterial line placement requires skilled personnel
• Telemedicine support for toxicity recognition
• Retrieval services if complications occur

Cultural Safety:

• Clear explanations of risks and monitoring requirements
• Family involvement in high-risk procedures
• Recognition of healthcare access barriers [296-305]

Māori Health Considerations

Health Context: Māori experience health inequities affecting perioperative care:

Chronic Disease Prevalence:

• Higher rates of cardiovascular and renal disease
• Careful assessment before using nitroprusside
• Lower threshold for alternative agents

Whānau Involvement:

• Include family in discussions about high-risk medications
• Explain monitoring and safety measures
• Respect for collective decision-making

Medication Safety:

• Ensure adequate monitoring regardless of location
• Rural Māori populations should have same standard of care
• Consider alternatives that don't require intensive monitoring if resources limited [306-310]

ANZCA Primary Exam Focus

High-Yield Facts

Must-Know Numbers:

• Dose: 0.5-10 mcg/kg/min (preferably ≤2 for prolonged use)
• Onset: <30 seconds
• Duration: 1-3 minutes
• Cyanide release: ~1 CN per molecule per minute
• Thiocyanate half-life: 2-4 days
• Toxicity dose threshold: >2 mcg/kg/min for >24-48 hours

Must-Know Mechanisms:

• NO release → guanylate cyclase → cGMP → vasodilation
• Cyanide release → cytochrome c oxidase inhibition → cellular hypoxia
• Detoxification: Rhodanese (liver) → thiocyanate → renal elimination
• Arterial + venous dilation (balanced)

Must-Know Contraindications:

• Compensatory hypertension (Cushing response, coarctation)
• Vitamin B12 deficiency
• Leber hereditary optic neuropathy (LHON)
• Increased ICP
• Severe hepatic/renal impairment

Must-Know Toxicity Signs:

• Metabolic acidosis with elevated lactate (earliest)
• Tachyphylaxis (loss of hypotensive effect)
• Elevated mixed venous O2 saturation
• Altered consciousness (late)

Must-Know Antidotes:

• Hydroxocobalamin (Cyanokit) 5g IV - first line
• Sodium thiosulfate 12.5g IV - adjunct
• 100% oxygen - enhances elimination [311-325]

Common MCQ Patterns

1. Mechanism: "Nitroprusside produces vasodilation via?" (Answer: NO release, cGMP increase)
2. Toxicity: "Signs of cyanide toxicity include?" (Answer: Metabolic acidosis, tachyphylaxis, elevated venous O2 sat)
3. Contraindications: "Contraindication to nitroprusside?" (Answer: B12 deficiency, increased ICP, compensatory HTN)
4. Antidote: "Treatment for cyanide toxicity?" (Answer: Hydroxocobalamin, thiosulfate, 100% O2)
5. Clinical use: "Drug of choice for controlled hypotension with least toxicity risk?" (Answer: Clevidipine or nicardipine preferred over SNP)
6. Pharmacokinetics: "Thiocyanate accumulation occurs in?" (Answer: Renal failure) [326-335]

Primary Viva Question Themes

Typical Viva Scenarios:

1. Mechanism:

   • "Tell me how nitroprusside works"
   • Expect: NO release, cyanide release, balanced arteriolar and venous dilation

2. Toxicity:

   • "A patient on SNP develops metabolic acidosis. What's happening?"
   • Expect: Cyanide toxicity mechanism, signs, treatment with hydroxocobalamin

3. Clinical application:

   • "Compare nitroprusside with clevidipine for controlled hypotension"
   • Expect: Onset/offset similar; SNP has cyanide toxicity; clevidipine safer

4. Contraindications:

   • "Why avoid nitroprusside in head injury with Cushing response?"
   • Expect: Compensatory hypertension, risk of cerebral ischemia

5. Combination therapy:

   • "Why give beta-blocker with nitroprusside?"
   • Expect: Control reflex tachycardia, reduce myocardial oxygen demand

Key Points to Emphasize:

• Cyanide toxicity is the major limitation
• Immediate onset/offset allows precise control
• Balanced arterial and venous dilation
• Contraindicated in B12 deficiency and compensatory HTN
• Hydroxocobalamin is the antidote of choice [336-345]

Assessment Content

SAQ Practice Question (20 marks)

Question:

A 55-year-old man is undergoing major spinal fusion surgery. Controlled hypotension is requested by the surgeon to reduce bleeding. Sodium nitroprusside infusion is commenced at 2 mcg/kg/min.

(a) Explain the mechanism of action of sodium nitroprusside, including how it produces vasodilation and the origin of its toxicity. (6 marks)

(b) After 3 hours, the patient requires increasing doses of nitroprusside (now 8 mcg/kg/min) to maintain target blood pressure. Arterial blood gas shows pH 7.28, PaCO2 38, HCO3 16, lactate 4.5 mmol/L. What is the likely diagnosis and what biochemical changes explain these findings? (6 marks)

(c) Describe the immediate management of this complication, including specific antidotes and their mechanisms. (4 marks)

(d) Outline strategies that could have prevented this complication. (4 marks)

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Model Answer:

(a) Mechanism of Action (6 marks)

Vasodilation Mechanism (3 marks):

1. Nitric Oxide Release: Sodium nitroprusside (SNP) spontaneously releases nitric oxide (NO) when it enters red blood cells and interacts with oxyhemoglobin. The nitroso group (NO+) donates NO.

2. cGMP Pathway: NO diffuses into vascular smooth muscle cells and activates soluble guanylate cyclase (sGC). This enzyme converts GTP to cyclic guanosine monophosphate (cGMP).

3. Smooth Muscle Relaxation: cGMP activates protein kinase G (PKG), which phosphorylates proteins leading to:

   • Sequestration of calcium into sarcoplasmic reticulum
   • Decreased calcium sensitivity of contractile proteins
   • Smooth muscle relaxation and vasodilation

Toxicity Origin (3 marks):

1. Cyanide Ligands: Each molecule of SNP contains five cyanide (CN-) ligands coordinated to the central iron atom. These are slowly released during metabolism.

2. Cyanide Release Mechanisms:

   • Spontaneous degradation in solution
   • Release during interaction with red blood cells (along with NO)
   • Higher doses and longer durations increase cumulative cyanide load

3. Toxicity Mechanism: Cyanide binds to cytochrome c oxidase in mitochondria, blocking the electron transport chain. This causes cellular hypoxia despite adequate oxygen delivery (histotoxic hypoxia), leading to anaerobic metabolism and lactic acidosis.

(b) Diagnosis and Biochemical Changes (6 marks)

Diagnosis (2 marks): Cyanide toxicity secondary to prolonged high-dose nitroprusside infusion.

Clinical picture supports this:

• Prolonged infusion (3 hours)
• High dose required (8 mcg/kg/min - above recommended 2 mcg/kg/min limit)
• Tachyphylaxis (loss of hypotensive effect, requiring dose escalation)
• Metabolic acidosis with elevated anion gap

Biochemical Changes (4 marks):

1. Metabolic Acidosis (pH 7.28, HCO3 16):

• Cyanide inhibits cytochrome c oxidase (complex IV of electron transport chain)
• Blocks oxidative phosphorylation
• Cells cannot use oxygen for aerobic metabolism
• Forced to use anaerobic glycolysis
• Accumulation of lactic acid (lactate 4.5 mmol/L)
• High anion gap metabolic acidosis (calculated anion gap = 140 - (104 + 16) = 20)

2. Elevated Lactate (4.5 mmol/L, normal <2):

• Anaerobic metabolism produces lactate from pyruvate
• Normal oxygen extraction impaired
• Tissue hypoxia at cellular level despite:
  • Adequate PaO2 (likely normal)
  • Adequate oxygen delivery
  • Normal or increased cardiac output

3. Normal PaCO2 (38 mmHg):

• Respiratory compensation for metabolic acidosis would typically lower PaCO2
• PaCO2 of 38 suggests inadequate respiratory compensation or timing (compensation takes 12-24 hours)
• Expected PaCO2 ≈ 1.5 × HCO3 + 8 = 1.5 × 16 + 8 = 32 mmHg
• Higher than expected suggests partial compensation or ventilatory limitation

4. Elevated Mixed Venous Oxygen Saturation (not given but characteristic):

• Tissues unable to extract oxygen due to blocked electron transport
• Venous blood returns with higher oxygen content than normal
• SvO2 typically >70-80% (normally 65-75%)

(c) Immediate Management (4 marks)

Immediate Actions (2 marks):

1. Discontinue nitroprusside immediately - stop the source of cyanide
2. 100% oxygen - hyperbaric if available; enhances cyanide elimination
3. Supportive care: Ensure adequate ventilation, circulation; prepare for cardiovascular collapse
4. Sodium bicarbonate: If pH <7.2, give 1-2 mEq/kg to correct acidosis (improves hemodynamics)

Specific Antidotes (2 marks):

1. Hydroxocobalamin (Cyanokit) - First Line:

• Dose: 5g IV over 15 minutes
• Mechanism: Binds cyanide to form cyanocobalamin (vitamin B12), which is non-toxic and excreted in urine
• Advantages: Rapid onset, highly effective, safe
• Side effects: Red discoloration of urine and skin (benign)
• Can repeat once if needed (total 10g)

2. Sodium Thiosulfate:

• Dose: 12.5g IV (or 150 mg/kg)
• Mechanism: Provides sulfur donor for the enzyme rhodanese in the liver to convert cyanide to thiocyanate (less toxic)
• Advantages: Readily available, inexpensive
• Limitations: Slower onset than hydroxocobalamin
• Role: Can give concurrently with hydroxocobalamin or as adjunct

Alternative (if above unavailable):

• Sodium nitrite: 300mg IV over 5-10 minutes (induces methemoglobin to bind cyanide; avoid in this patient due to hypotension risk)

(d) Prevention Strategies (4 marks)

Dose and Duration Limitations (1 mark):

• Limit maximum dose to ≤2 mcg/kg/min for prolonged use
• Preferably <10 mcg/kg/min absolute maximum
• Limit duration to <4-6 hours
• Use alternative agents (clevidipine, nicardipine) for prolonged controlled hypotension

Prophylactic Measures (1 mark):

• Coadminister sodium thiosulfate: Provides sulfur for cyanide detoxification
  • Dose: 1:10 ratio with nitroprusside (e.g., 10 mg thiosulfate per 1 mg nitroprusside)
  • Mechanism: Enhances rhodanese activity
• 100% oxygen: Enhances cyanide elimination

Monitoring (1 mark):

• Regular ABG monitoring every 4-6 hours with prolonged use
• Monitor serum lactate (early indicator of toxicity)
• Monitor for tachyphylaxis (loss of hypotensive effect)
• Monitor urine output and renal function
• Hemodynamic monitoring (arterial line mandatory)

Patient Selection (1 mark):

• Avoid in patients with:
  • Hepatic impairment (reduced rhodanese activity)
  • Renal impairment (thiocyanate accumulation)
  • Vitamin B12 deficiency
  • Leber hereditary optic neuropathy (LHON)
  • Malnutrition (depleted thiosulfate stores)
• Consider alternative agents in high-risk patients

Total: 20 marks

Primary Viva Scenario (15 marks)

Examiner: A patient is receiving nitroprusside for controlled hypotension during spine surgery. Tell me about the mechanism of action and the risks.

Candidate:

Mechanism of Action (3 marks): "Nitroprusside is a direct-acting vasodilator that works by releasing nitric oxide. The mechanism involves:

1. NO Release: When nitroprusside enters the bloodstream, particularly red blood cells, it spontaneously releases nitric oxide (NO).

2. cGMP Pathway: NO diffuses into vascular smooth muscle cells and activates soluble guanylate cyclase, which converts GTP to cyclic GMP.

3. Vasodilation: cGMP causes smooth muscle relaxation through calcium sequestration, leading to dilation of both arterioles and veins - it's a balanced vasodilator affecting both preload and afterload."

Examiner: What makes it different from other vasodilators like GTN?

Candidate:

Comparison with Nitroglycerine (3 marks): "The key differences are:

1. Site of Action: Nitroprusside dilates both arteries and veins equally. Nitroglycerine primarily dilates veins more than arteries - it's predominantly a preload reducer.

2. Speed: Nitroprusside has immediate onset (<30 seconds) and very short duration (1-3 minutes). GTN takes 1-2 minutes to work and lasts 5-10 minutes.

3. Toxicity: This is the major difference - nitroprusside contains five cyanide molecules and releases cyanide, which can cause toxicity. GTN does not contain cyanide and has a different toxicity profile (methemoglobin at very high doses only)."

Examiner: Tell me about the cyanide toxicity risk.

Candidate:

Cyanide Toxicity (3 marks): "Cyanide toxicity is the major limitation of nitroprusside:

Mechanism:

• Each nitroprusside molecule contains five cyanide ligands
• These are slowly released during metabolism
• Cyanide binds to cytochrome c oxidase in mitochondria
• This blocks the electron transport chain
• Cells cannot use oxygen for aerobic metabolism
• Result: Cellular hypoxia and lactic acidosis despite adequate oxygen delivery

Risk Factors:

• High doses (>2 mcg/kg/min for >24-48 hours)
• Prolonged infusions
• Hepatic impairment (reduced rhodanese activity for detoxification)
• Renal impairment (reduced thiocyanate elimination)
• Vitamin B12 deficiency
• Malnutrition (depleted thiosulfate stores)

Clinical Signs:

• Metabolic acidosis with elevated lactate (earliest sign)
• Tachyphylaxis - requiring increasing doses to maintain effect
• Elevated mixed venous oxygen saturation (tissues can't extract oxygen)
• Altered mental status, confusion (late sign)"

Examiner: How would you treat cyanide toxicity?

Candidate:

Treatment (3 marks): "The treatment for cyanide toxicity involves:

Immediate:

1. Stop nitroprusside immediately
2. Give 100% oxygen - this enhances cyanide elimination
3. Supportive care - ensure adequate ventilation and circulation

Specific Antidotes:

1. Hydroxocobalamin (Cyanokit) - first line: 5g IV over 15 minutes. This is vitamin B12 precursor that binds cyanide to form non-toxic cyanocobalamin, which is excreted in urine. Safe and highly effective.

2. Sodium thiosulfate - 12.5g IV. This provides sulfur for the enzyme rhodanese in the liver to convert cyanide to thiocyanate, which is much less toxic and eliminated by the kidneys.

3. These can be given together for synergistic effect.

Supportive:

• Correct metabolic acidosis with sodium bicarbonate if severe
• Hemodialysis can remove thiocyanate if renal failure present
• Cardiovascular support with fluids and vasopressors if needed"

Examiner: How can you prevent this complication?

Candidate:

Prevention (3 marks): "Prevention strategies include:

Dose and Duration:

• Limit dose to preferably ≤2 mcg/kg/min
• Absolute maximum 10 mcg/kg/min
• Limit duration to <4-6 hours
• Switch to alternative agents like clevidipine for prolonged procedures

Prophylaxis:

• Give sodium thiosulfate prophylactically in a 1:10 ratio with nitroprusside dose
• This provides sulfur for cyanide detoxification

Monitoring:

• Regular ABGs and lactate levels every 4-6 hours
• Monitor for tachyphylaxis (escalating doses needed)
• Invasive arterial pressure monitoring
• Monitor renal and hepatic function

Patient Selection:

• Avoid in hepatic or renal impairment
• Avoid in vitamin B12 deficiency
• Use alternative agents in high-risk patients"

Examiner: Thank you. That's a comprehensive understanding of nitroprusside and its complications.

Total: 15 marks

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References

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2. Rindone JP, Sloane EP. Cyanide toxicity from sodium nitroprusside: risks and management. Ann Pharmacother. 1992;26(4):515-519. PMID: 1531057

3. Vesey CJ, Cole PV, Linnell JC, et al. Some metabolic effects of sodium nitroprusside in man. Br Med J. 1976;1(6010):506-508. PMID: 1252877

4. Baskin SI, Horowitz AM, Nealley EW. The antidotal action of sodium nitrite and sodium thiosulfate against cyanide poisoning. J Clin Pharmacol. 1992;32(4):368-375. PMID: 1569238

5. Hall AH, Rumack BH. Hydroxocobalamin/sodium thiosulfate as a cyanide antidote. J Emerg Med. 1987;5(2):115-121. PMID: 3295013

6. Curry SC, Arnold-Capell P. Nitroprusside, nitroglycerin, and angiotensin-converting enzyme inhibitors. Crit Care Clin. 1991;7(3):555-582. PMID: 1863969

7. Royster RL, Butterworth JF 4th, Prough DS, et al. Preoperative infusion of saralasin or placebo in patients with severe hypertension. Anesth Analg. 1987;66(7):669-676. PMID: 3602358

8. Marik PE, Varon J. Requirement of perioperative stress doses of corticosteroids: a systematic review of the literature. Arch Surg. 2008;143(12):1222-1226. PMID: 19075191

9. Varon J, Marik PE. The diagnosis and management of hypertensive crises. Chest. 2000;118(1):214-227. PMID: 10893382

10. Deeks ED. Clevidipine: a review of its use for managing blood pressure in perioperative and intensive care settings. Drugs. 2013;73(16):1775-1802. PMID: 24129763

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