Ketamine

Introduction Overview

Generic Name

Ketamine

Brand Name

Ketalar

Dosage Form

Injection 200 mg/20 mL (10 mg/mL), 500 mg/10 mL (50 mg/mL), and 500 mg/5 mL (100 mg/mL)

Drug Class

General anesthetics

Pharmacokinetics

Absorption: Ketamine is typically administered via intravenous (IV) or intramuscular (IM) injection for anesthetic purposes. Upon IV administration, ketamine is rapidly absorbed with an onset of action within 30 seconds, providing surgical anesthesia for up to 10 minutes with doses of 1 to 2 mg/kg. IM administration results in a slightly slower onset, with anesthesia induced within minutes and a longer duration, approximately 12 to 25 minutes depending on the dose (6.5 to 13 mg/kg). The bioavailability of ketamine via intramuscular route is high due to rapid muscle perfusion. Oral and other routes are investigational mostly for off-label uses such as depression, but bioavailability through oral routes is substantially lower due to first-pass metabolism. Distribution: Ketamine exhibits a large volume of distribution, reflecting extensive tissue penetration, particularly in highly perfused organs such as the brain, heart, and lungs. It crosses the blood-brain barrier readily, which accounts for its prompt anesthetic and psychotropic effects. Approximately 12-50% of ketamine is bound to plasma proteins, primarily albumin. The rapid distribution phase typically lasts 10-15 minutes, after which the drug redistributes into peripheral tissues contributing to the termination of clinical effects. Metabolism: Ketamine undergoes hepatic metabolism primarily via N-demethylation by cytochrome P450 enzymes CYP2B6, CYP3A4, and CYP2C9 into norketamine, an active metabolite with about one-third to one-fifth the anesthetic potency of the parent compound. Norketamine is further hydroxylated and conjugated to water-soluble metabolites. The metabolism shows substantial interindividual variability influenced by genetic polymorphisms and concomitant medications. The metabolism also accounts for the reduced bioavailability of oral ketamine due to first-pass hepatic clearance. Elimination: Ketamine and its metabolites are primarily eliminated renally. The elimination half-life of ketamine ranges from 2 to 3 hours after IV administration. Approximately 90% of ketamine metabolites are excreted in urine within 24 hours. Minor biliary excretion may also occur. Factors such as hepatic impairment can prolong elimination half-life and enhance sedative effects. In clinical practice, the elimination kinetics inform dosing intervals especially in repeated or continuous infusion protocols used for anesthesia or depression therapy.

Dosage Forms

Available Dosage Forms: Ketamine is supplied as an injectable solution in multiple concentrations. These include injection vials containing 200 mg per 20 mL (10 mg/mL), 500 mg per 10 mL (50 mg/mL), and 500 mg per 5 mL (100 mg/mL). The injection is intended for intravenous or intramuscular use only. Other formulations, such as intranasal sprays (e.g., esketamine nasal spray 'Spravato') and oral or sublingual tablets, exist primarily for off-label or investigational use, particularly in treatment-resistant depression, but these are not FDA-approved ketamine formulations. Dosages for Adults and Adolescents: For anesthesia induction, intravenous ketamine is administered at doses of 1 to 4.5 mg/kg, often starting at 1 to 2 mg/kg given slowly over 60 seconds to avoid adverse hemodynamic responses. Maintenance dosing consists of incremental doses of half to the full induction dose repeated as clinically necessary. Intramuscular induction doses range from 6.5 to 13 mg/kg with maintenance dosing similar to IV administration. In patients 16 years and older, adult dosing guidelines apply. For off-label use in depression, doses and regimens vary, with clinical trials employing sub-anesthetic doses via IV infusion (e.g., 0.5 mg/kg over 40 minutes), intranasal sprays, or oral forms, often administered once or multiple times weekly. Specific Patient Populations: In pediatric patients younger than 16 years, dosing must be carefully titrated with close monitoring given risks of neurotoxicity and altered pharmacokinetics. Particular caution is warranted in patients with cardiovascular disease or uncontrolled hypertension due to ketamine’s potential to cause significant elevations in blood pressure and heart rate. Use is contraindicated in patients with hypersensitivity to ketamine or its excipients. Adjustments in dosing and administration rate are recommended in patients with hepatic impairment due to slower metabolism and prolonged elimination, as well as in those who have consumed CNS depressants or substances that interact pharmacodynamically. The slow administration over at least 60 seconds is critical in all populations to mitigate risks of respiratory depression and emergence phenomena.

Mechanism Of Action

Ketamine is classified as a dissociative anesthetic primarily due to its unique mechanism of action at the molecular level. Its primary target is the N-methyl-D-aspartate (NMDA) receptor, a subtype of glutamate receptors in the central nervous system. Ketamine acts as a non-competitive antagonist at the NMDA receptor by binding to the phencyclidine site within the receptor channel, thereby blocking the excitatory neurotransmitter glutamate from activating the receptor. This blockade disrupts neural transmission associated with pain perception, memory formation, and consciousness. At the cellular level, ketamine’s inhibition of NMDA receptors decreases excitatory synaptic transmission, which leads to sedation, analgesia, and anesthesia. Additionally, ketamine modulates several other neurotransmitter systems including opioid receptors (mu, delta, and kappa), monoaminergic pathways, and voltage-gated calcium channels. These ancillary effects may contribute to its analgesic and antidepressant properties by influencing descending pain modulation pathways and neural plasticity. Biochemically, ketamine’s blockade of NMDA receptors leads to altered intracellular calcium influx and changes in downstream signaling pathways such as mTOR (mechanistic target of rapamycin), which has been implicated in its rapid antidepressant effects. This contrasts traditional antidepressants that operate over weeks, highlighting ketamine’s clinical significance in treatment-resistant depression. Compared to other general anesthetics such as propofol or barbiturates that enhance GABAergic inhibition, ketamine’s unique dissociative and psychomimetic effects are characteristic of NMDA receptor antagonism. Clinical trials and research demonstrate that sub-anesthetic doses of ketamine rapidly alleviate depressive symptoms, presumably via restoration of synaptic connectivity and reversal of stress-induced neural deficits. However, ketamine's ability to induce psychotomimetic effects stems from its impact on NMDA receptor-mediated neural circuits, necessitating careful clinical monitoring. Overall, ketamine’s multifunctional mechanism underpins its versatile clinical applications, ranging from anesthesia to emerging psychiatric treatments.

Pharmacological Actions

Non-competitive antagonist of NMDA receptors causing dissociative anesthesia.
Analgesic effect via inhibition of excitatory glutamatergic neurotransmission.
Rapid antidepressant effects by modulation of neural plasticity and mTOR pathways.
Sedative properties with preservation of airway reflexes at clinical doses.
Sympathomimetic activity leading to increased heart rate and blood pressure.
Modulation of opioid receptors contributing to analgesia.
Psychotomimetic effects due to alterations in cortical and subcortical networks.
Antiemetic effects mediated by central nervous system actions in some instances.
Bronchodilator properties beneficial in asthmatic or bronchospasm-prone patients.
Minimal respiratory depression compared to other anesthetic agents at appropriate doses.
Induction of altered sensory perception and detachment from the environment.
Neuroprotective effects in certain ischemic models by attenuating excitotoxicity.
Potential hepatotoxicity with prolonged or high-dose exposure.
Stimulation of sympathetic nervous system contributing to hemodynamic changes.
Increased cerebrospinal fluid pressure in susceptible individuals.

Therapeutic Or Clinical Uses

Induction and maintenance of general anesthesia for diagnostic and surgical procedures.
Anesthetic in pediatric and adult patients when skeletal muscle relaxation is not required.
Supplement to other anesthetic agents to enhance anesthesia depth and analgesia.
Off-label treatment for treatment-resistant depression via intravenous infusions or nasal formulations.
Emerging investigational treatments for psychiatric disorders such as bipolar depression and PTSD.
Analgesic adjunct in acute pain management settings and procedural sedation.
Use in emergency medicine for rapid sequence intubation due to preservation of airway reflexes.
Anesthetic agent in patients with bronchospasm due to bronchodilatory effects.
Used in burn and trauma patients requiring anesthesia but with compromised hemodynamics.
Potential treatment for neuropathic and chronic pain syndromes under research.
Employed in veterinary anesthesia and analgesia (non-human use).
Use in field or battlefield anesthesia because of rapid onset and maintenance of cardiovascular stability.
Explored in treatment of substance use disorders given its neurochemical effects.
Investigation into sublingual, oral, and intranasal formulations for outpatient psychiatric therapy.
Potential off-label use in refractory status epilepticus as part of anesthetic protocol.

Side Or Adverse Effects

Emergence reactions including hallucinations, vivid dreams, and delirium upon recovery from anesthesia.
Confusion, disorientation, or a dream-like state during emergence.
Transient hypertension and tachycardia due to sympathetic stimulation.
Respiratory depression, especially with rapid IV administration or overdose.
Slow heart rate (bradycardia) and arrhythmias in rare cases.
Jerky muscle movements or convulsions resembling seizure activity.
Painful or difficult urination, increased frequency, loss of bladder control, or hematuria.
Nausea and vomiting, although less common than with other anesthetics.
Allergic reactions ranging from mild rash to anaphylaxis.
Increased intracranial and intraocular pressure requiring careful use in head injury patients.
Liver injury associated with prolonged or repeated exposure.
Potential for psychological dependence and abuse due to psychotomimetic and hallucinogenic effects.
Urinary tract dysfunction including ulcerative cystitis with chronic abuse.
Long-term cognitive impairment and memory deficits with repeated recreational use.
Sedation and delayed recovery leading to impaired psychomotor functions post-anesthesia.

Precautions

Use caution in patients with hypertension or cardiovascular disease due to potential for hemodynamic instability.
Avoid use in patients with known hypersensitivity to ketamine or any formulation excipients.
Monitor patients closely for emergence reactions and provide supportive care as needed.
Administer ketamine slowly over at least 60 seconds IV to minimize respiratory depression and hemodynamic responses.
Use caution in patients with elevated intracranial or intraocular pressure; monitor neurological status carefully.
Avoid using ketamine as sole anesthetic for procedures involving the pharynx, larynx, or bronchial tree due to preserved airway reflexes.
Consider risks of pediatric neurotoxicity; use minimized doses and discuss risks with caregivers for children under 3 years old.
Use with care in patients with liver impairment due to potential for delayed metabolism and toxicity.
Ensure adequate oxygenation and ventilation during ketamine use, especially in patients at risk for respiratory depression.
Avoid concomitant use with CNS depressants such as opioids, benzodiazepines, and muscle relaxants without close monitoring.
Be aware of potential for psychological dependence; limit repeated or high-dose administration where possible.
Regularly assess bladder function in patients receiving repeated ketamine doses.
Use stringent sterile techniques and monitoring when administering ketamine infusion therapy for psychiatric conditions.
Avoid self-administration or unsupervised use of compounded or oral ketamine formulations due to FDA warnings.
Adjust monitoring and dosing in alcoholic patients or those with alcohol intoxication to reduce risk of fatal interactions.

Warnings

Potential for emergence reactions including hallucinations and delusions upon waking from anesthesia.
Risk of significant transient increases in blood pressure, heart rate, and cardiac workload; monitor cardiovascular parameters closely.
Respiratory depression may occur with rapid administration or overdose; maintain airway and ventilatory support.
Ketamine does not suppress pharyngeal and laryngeal reflexes; avoid sole use for airway instrumentation requiring muscle relaxation.
FDA warning regarding compounded oral ketamine products for psychiatric use due to lack of safety and efficacy data.
Ketamine use may increase cerebrospinal fluid pressure; caution warranted in patients with increased intracranial pressure.
Drug-induced liver injury has been reported, especially with chronic or high-dose usage.
Risk of pediatric neurotoxicity with repeated or prolonged exposure in children under 3 years.
Possibility of psychological dependence and abuse; known as a Schedule III controlled substance.
Increased risk of adverse events when combined with alcohol or certain stimulants such as caffeine.
Risks of infectious complications due to needle sharing in illicit use.
Avoid use in patients with untreated or uncontrolled hypertension.
Potential for urinary tract damage and ulceration with chronic abuse.
Ketamine may impair mental and motor functions for several hours; avoid driving or hazardous tasks post-administration.
Emergency medical attention needed in cases of allergic reactions or severe adverse events.

Contraindication

Known hypersensitivity or allergy to ketamine or any ingredient in the formulation.
Untreated or uncontrolled hypertension due to risk of exacerbation.
Conditions where significant elevations in blood pressure are contraindicated, such as severe cardiovascular disease.
Use as sole anesthetic in surgery or diagnostic procedures requiring skeletal muscle relaxation, especially of the airway.
Patients with a history of psychosis or severe psychiatric illness requiring caution due to potential worsening symptoms.
Severe liver impairment where ketamine metabolism is compromised.
Patients with elevated intracranial pressure without adequate monitoring.
Pregnancy when anesthesia can be delayed or avoided unless benefits outweigh risks.
Use in neonates and infants under experimental conditions given risks of neurotoxicity without clear benefit.
Use of compounded oral or intranasal ketamine formulations outside of approved indications or away from medical supervision.
Patients with significant respiratory compromise who cannot be adequately supported.
Situations where monitored anesthesia care is unavailable.
Concurrent use with other drugs that may potentiate respiratory or cardiovascular depression without monitoring.
History of ketamine abuse or dependence without access to supervised treatment.
Any condition deemed by the healthcare provider to pose an unacceptable risk from ketamine administration.

Drug Interactions

Additive CNS depressant effects with opioids, benzodiazepines, muscle relaxants, and alcohol leading to increased sedation and respiratory depression.
Potential attenuation of ketamine metabolism by CYP450 inhibitors such as fluoxetine and quinidine, increasing ketamine plasma levels.
Enhanced sympathomimetic effects when combined with sympathomimetic drugs (e.g., epinephrine, amphetamines) leading to hypertension and tachycardia.
Interactions with theophylline and aminophylline may alter ketamine’s cardiac and CNS effects.
Concomitant use with vasopressin may potentiate cardiovascular responses.
Benzodiazepines may decrease ketamine-induced emergence reactions but can potentiate sedation risk.
Alcohol consumption increases risk of respiratory depression and hypotension when combined with ketamine.
Pharmacodynamic interactions with other NMDA antagonists (e.g., dextromethorphan) may enhance psychotomimetic effects.
Avoid combining with other anesthetics without dose adjustment due to additive anesthetic and cardiovascular effects.
Interactions with CYP3A4 and CYP2B6 inducers (e.g., rifampin) may reduce ketamine effectiveness through increased metabolism.
Use with caution when combined with drugs affecting intracranial pressure.
Possible increased risk of hepatotoxicity when used with other hepatotoxic medications.
Drugs affecting urinary bladder function may exacerbate ketamine-associated urinary adverse effects.
Herbal supplements and vitamins may alter hepatic metabolism but data are limited; disclose all supplements to healthcare provider.
Sedation and mental impairment risks increased when combined with CNS depressants, requiring monitoring.

Preparations Of The Drug

Injectable solutions of ketamine hydrochloride: 200 mg per 20 mL (10 mg/mL) in vials for IV or IM use.
Injectable concentrate formulations: 500 mg per 10 mL (50 mg/mL) and 500 mg per 5 mL (100 mg/mL) for dilution and dosing flexibility.
Intranasal esketamine (Spravato) nasal spray, FDA-approved for treatment-resistant depression under strict medical supervision.
Compounded oral, sublingual, and slow-release ketamine formulations are used in some clinical trials or off-label psychiatric treatments but are not FDA-approved.
Sterile formulations intended for hospital and controlled clinical environments with strict storage (20–25 °C) and handling requirements.
Formulations free of preservatives for intravenous infusion preparations in anesthesia and research.
No commercially available oral ketamine tablets approved by the FDA; only compounded or investigational use.
Storage recommendations specify protection from light and maintaining recommended temperature to preserve drug stability.
Commercially available preparations are Schedule III controlled substances requiring careful inventory and dispensing controls.
Ketamine injection is supplied with a sterile, pyrogen-free aqueous solution of ketamine hydrochloride for safe parenteral administration.
Multi-dose vials for operating room or clinical use allowing for multiple administrations per vial with aseptic technique.
Availability of generic and brand name Ketalar formulations with consistent pharmacological potency.
No topical or transdermal formulations currently approved for human use.
Preparations intended exclusively for single-dose administration in acute anesthesia or sedation settings.
Emerging formulations being studied include intranasal sprays, oral dissolvable films, and extended-release tablets mainly for psychiatric indications.