KETAMINE

  • Know ketamine well – important ED drug. Know PK, PD and toxicities.
Structure/Class
  1. Phencyclidine derivative
Pharmacodynamics
  1. NMDA receptor antagonist. It is the only IV anaesthetic agent that has significant analgesic properties
  2. Organ system effects as follows:
    • CNS
      • It is a cerebral vasodilator and tends to increase cerebral blood flow and cerebral metabolic rate. Therefore, it is contra-indicated in RICP.
      • May be used for status epilepticus if other means are unsuccessful.
      • Emergence phenomenon – tends to be less severe and of lower incidence in children. Premedication with BZD may decrease incidence.
    • CVS
      • It produces transient by significant centrally mediated stimulation, therefore increasing HR and cardiac output.
      • It is thought to be a direct myocardial depressant, and this property may become apparent in the patients that are critically ill and have limited ability to increase their sympathetic drive.
    • Respiratory
      • Transient apnoea and hypoventilation if large dose given rapidly.
      • Importantly – causes lacrimation and salivation. May cause laryngospasm in children.
      • Relaxes bronchial s/m: consider in severe asthma
      • If used as a single drug, the respiratory response to hypoxia and hypercapnia is NOT affected
Absorption/administration
  1. IV or IM.
  2. Can be given as bolus/infusion
Distribution
  1. Very lipid soluble
  2. Only IV anaesthetic agent that has low protein binding
  3. Large Vd – 3L/kg
Metabolism
  1. Metabolised in the liver to norketamine (an active metabolite) and then conjugated to water soluble metabolites and excreted in the urine.
    • Distribution T ½: 11-16 minutes
    • Elimination T ½ : 2-4 hours
    • Duration of action: 5-10 minutes
Excretion
  1. Urine
Indications
  1. Procedural sedation (Very useful in children – give IM)
  2. Intravenous anaesthetic for induction
  3. Pain management
Contraindications
  1. Head injury and RICP are absolute CI.
Special precautions
Interactions
Adverse events
  1. Salivation/bronchorrhoea, leading to laryngospasm
  2. Emergence phenomena
  3. RICP
Dosing/administration
  1. 1-2mg/kg if induction
  2. Pain dose is 0.1mg/kg, infusion is 0.1mg-0.3mg/kg
  3. 4mg/kg IM if procedural sedation
Toxicology
Withdrawal syndrome
Special notes