Phencyclidine derivative, dissociative anaesthetic, analgesic, preserver of tone in larynx/pharynx
Used in the US Army in 1962, Vietnam. Civilian use ensued in 1970.
Racemic mixture of isomers (optical isomer/chiral). pKa of 7.5.
One of the isomers, s+ketamine is more potent and has a faster recovery time.
Ketamine has a high lipid solubility (5–10 times that of thiopental) and crosses the blood-brain barrier faster.
Norketamine (a metabolite) has 20–30% of the activity of the parent compound.
- ↑HR, BP, CO due to ↑sympathetic tone
- Baroreceptor function preserved
- Stimulates respiration, preserved AW reflexes
- ?↑IOP, ICP, CMRO2 - research ongoing
- Amnesia common and sometimes useful
- Visceral pain poorly obtunded
- LA at higher doses
- Emergence delirium and hallucinations- ?need benzo
- PONV common
- ↑Uterine tone and ↑catecholamines
- Rashes in 15%
- Can work epidurally(!)
Non-competative antagnoism of NMDA receptors at both Ca2+ pore and phencyclidine binding site- modulates mACh and opioid receptors
Loss alpha-rhythm and theta predominance on EEG
+ve ionotrope ?due to cAMP and calcium influx
30-60s onset IV (3-4mins IM), Peak at 1 minute. 5 - 20 minute duration depending on dose.
Good For Bronchospastic or Hypotensive Patients
Good oral absorption but unfortunately only 20% available due to first pass metabolism
Distribution and elimination are slower if halothane, benzos or barbituates are concurrently administered.
1.5-2mg/kg in IV induction
A higher incidence is associated with factors such as increasing age, female gender, patients who normally dream, rapid intravenous administration, and large doses. Benzo use can reduce the effect.
Dr. David Lyness
0.15- 0.25mg/kg bolus for analgesia (17.5mg in 70kg)
0.5-3mg/kg/hr for infusion (35mg-210mg/hr in 70kg)
Hypersalivation can occur; glycopyrolate can alleviate this
Ketamine for Analgesia
20mg over 10mins then 20mg/hr titrated to effect.
Paeds IM Sedation - 4 mg/kg intramuscular as initial dose.
One booster dose of 2 mg/kg is allowed after 10m
Bioavailability of the intranasal ketamine is between 40-50%
SL dose can be higher in certain indications
Mixes of ketamine are used in some practices:
combined with PROPOFOL (KETOFOL) or MAGNESIUM (KETANESIUM)