Pharm 101: Ketamine

Class

Sedative-hypnotic

Pharmacodynamics

• NMDA receptor antagonist: inhibits reuptake of catecholamine and serotonin
• Multiple organ system effects
• CNS:
  • Dissociative anaesthesia
  • Analgesia
  • Raised intracranial pressure (ICP)
  • May have anticonvulsant properties
• CVS:
  • Increases heart rate, blood pressure and cardiac output
• Respiratory:
  • Intact airway reflexes
  • Minimal respiratory depression
  • Lacrimation and salivation that may cause laryngospasm in children
  • Bronchodilator effect
• Ocular:
  • Nystagmus

Pharmacokinetics

• Highly lipid soluble, hence rapid onset
• Effect terminated by redistribution to inactive tissue sites
• Low protein binding 12%
• Liver metabolism:
  • Demethylation (CYP450) to nor-ketamine (1/4 potency of ketamine)
  • Nor-ketamine is hydroxylated and conjugated into water soluble inactive metabolites excreted in urine

Clinical uses

• Anaesthesia:
  • Induction dose 1-2 mg/kg IV
  • Maintenance dose 30-90 mcg/kg/min (less common)
• Analgesic agent:
  • Small bolus doses of 10-20mg
• Status epilepticus
• Acute asthma

Adverse effects

• Emergence reactions
• Laryngospasm
• Vomiting
• Hypersalivation
• Raised ICP
• Hypertension and tachycardia

Further Reading

• Nickson C. Ketamine RSI for head injury
• Nickson C. Intubation, Hypotension and Shock