Induction agent · Analgesic · Sedative · Bronchodilator
Ketamine
Indications
- RSI induction, favored in bronchospasm; reduced doses in shock
- Dissociative sedation for painful procedures, IV or IM
- Sole anesthetic for short procedures that need no muscle relaxation (label)
- Sub-dissociative analgesia and opioid sparing (off-label)
- Severe agitation, IM (off-label)
- Refractory status epilepticus or status asthmaticus by infusion (off-label)
Dosing
Ketamine drip card and mL/h converterStart: Analgesia 0.1–0.3 mg/kg/h (sub-dissociative); sedation 0.5–2 mg/kg/h
| Where | Dose |
|---|---|
| Airway and RSI | Ketamine: 1–2 mg/kg (0.5–1 in shock); bronchodilates; keeps BP |
| Seizures and neuro | Ketamine: 1 mg/kg IV or 4–5 mg/kg IM for severe agitation (EMS) |
| Other common pushes | Ketamine (analgesia): 0.1–0.3 mg/kg IV over 10 min |
On the quick cards
Mechanism of action
Ketamine is a non-competitive NMDA receptor antagonist. It enters open channels and binds the phencyclidine site in the pore, blocking Ca²⁺ and Na⁺ entry, so block builds with neuronal activity. Blocking NMDA receptors on inhibitory interneurons and in thalamocortical and limbic circuits dissociates the cortex from sensory input, and dorsal horn block prevents wind-up and central sensitization. Weaker actions at opioid receptors, HCN1 channels and monoamine transporters add to the effect.
Pharmacology
- CNS: dissociative anesthesia (eyes open, nystagmus, catalepsy) with analgesia and amnesia; analgesia alone at low doses; raises cerebral blood flow; emergence reactions in about 12% (label)
- Cardiovascular: raises heart rate, cardiac output and BP (10–50%, label) through central sympathetic outflow and blocked catecholamine reuptake; direct negative inotropy shows when catecholamines are depleted
- Respiratory: drive largely preserved; bronchodilates through catecholamine release, direct smooth muscle relaxation and vagal block; airway reflexes mostly kept but not protective; more secretions
- Other: raises intraocular pressure and muscle tone; nausea; repeated use can injure the bile ducts and bladder
Pharmacokinetics
| Onset | About 30 s IV; 3–4 min IM (label) |
|---|---|
| Duration | 5–10 min IV, 12–25 min IM (label); full recovery takes longer |
| Half-life | Distribution 10–15 min; elimination about 2.5 h (label) |
| Distribution | Vd about 3 L/kg; very lipid-soluble, so fast brain uptake, then redistribution |
| Protein binding | Low, about 10–50% (sources vary) |
| Metabolism | CYP2B6 and CYP3A4 to norketamine (about one-third as potent), then hydroxylation and conjugation |
| Clearance | High, about 12–20 mL/kg/min, near liver blood flow |
| Elimination | Urine, almost all as metabolites |
| Bioavailability | High IM; about 45–50% intranasal; about 20% oral (first pass) |
Chemistry
- 2-(2-chlorophenyl)-2-(methylamino)cyclohexanone, an arylcyclohexylamine related to phencyclidine
- One chiral carbon; Ketalar is racemic. S-ketamine (esketamine) has 3–4 times the NMDA affinity and potency of R-ketamine; in the US it is sold only as a nasal spray (Spravato) for depression
- pKa 7.5: just over half ionized at pH 7.4, yet lipid-soluble enough for fast brain entry
- Water-soluble hydrochloride at 10, 50 and 100 mg/mL, pH 3.5–5.5, with benzethonium chloride; dilute the 100 mg/mL strength before IV use (label)
Adverse effects and cautions
In the one-pagers
- Airway and RSIRSI drugs: Ketamine: 1–2 mg/kg: About 30 s: Raises HR, BP; bronchodilates; emergence
- Asthma and COPD ExacerbationsVentilating obstructed lungs: Ketamine is a useful induction drug in asthma (bronchodilates)
- Sedation, Pain and Delirium ScalesWhy analgesia-first light sedation: Pain: Low-dose ketamine adjunct after surgery: Conditional
- Mental Health: Meds and CommunicationStimulant toxicity: AHA 2023 recommends sedation for severe agitation, naming benzodiazepines, antipsychotics and ketamine, and rates prolonged physical restraint without sedation as harmful; AHA 2025 prefers ice-water immersion for life-threatening hyperthermia. Check temperature, glucose, potassium, CK, creatinine, troponin and an ECG, and give fluids for rhabdomyolysis.
- Pulmonary EmbolismSupporting the failing RV: Intubation can trigger arrest: induction drops SVR, positive pressure cuts venous return, apnea raises CO₂ and PVR. If unavoidable: norepinephrine running, expert operator, preoxygenate, reduced-dose etomidate or ketamine, VT 6 mL/kg, plateau <30, low PEEP, ECMO team aware.
- Right Heart Failure and Pulmonary HypertensionIntubation and home prostacyclin: Etomidate or reduced-dose ketamine; avoid propofol boluses; keep apnea short.
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Sources
- FDA label: Ketalar (2026)
- PubChem: ketamine
- Gao 2016 (review)
- Casey 2025 (RSI trial)
For education and exam preparation only. Follow your institution’s protocols. Typical adult values for study. Follow the order, the label and your institution's protocols.