Ketamine: Effects, Uses and Side Effects

What is Ketamine?

Ketamine is a dissociative anesthetic that has been used in medicine since the 1960s. It is listed on the World Health Organization (WHO) List of Essential Medicines and remains a cornerstone drug in anesthesia, emergency medicine, and pain management worldwide.

Mechanism of Action

Ketamine primarily acts as an NMDA receptor antagonist. It blocks the N-Methyl-D-Aspartate (NMDA) receptor in the brain, which plays a key role in pain transmission and consciousness. This blockade produces a state known as dissociative anesthesia: the patient is disconnected from their environment and feels no pain, while typically retaining protective reflexes (such as the swallowing reflex) and spontaneous breathing. In addition to its anesthetic properties, ketamine also has analgesic (pain-relieving), sedative, and bronchodilatory (airway-widening) effects.

Indications and Clinical Uses

• Anesthesia induction and maintenance: especially in hemodynamically unstable patients (e.g., shock)
• Emergency and pre-hospital medicine: rapid analgesia and sedation even under difficult conditions
• Pain management: for acute and chronic pain conditions unresponsive to other treatments
• Pediatrics: commonly used for short procedures in children due to preservation of protective reflexes
• Psychiatry / depression treatment: Esketamine (an isomer of ketamine) is approved as a nasal spray (Spravato) for treatment-resistant depression
• Intensive care: as part of sedation protocols for mechanically ventilated patients

Dosage and Administration

Ketamine can be administered intravenously (IV), intramuscularly (IM), intranasally, orally, or subcutaneously. The exact dosage depends on the patient's body weight, the type of procedure, and the desired level of anesthesia. Typical doses for anesthesia induction are 1–2 mg/kg body weight IV or 4–6 mg/kg IM. Administration must always occur under medical supervision in an appropriate clinical setting.

Side Effects

Like all medications, ketamine can cause side effects:

• Psychological reactions: hallucinations, nightmares, confusion, and so-called emergence reactions (unpleasant experiences upon awakening) -- more common in adults than children
• Increased blood pressure and heart rate: ketamine stimulates the sympathetic nervous system
• Elevated intraocular and intracranial pressure: historically a concern in certain conditions (e.g., glaucoma, traumatic brain injury), though more recent evidence has revised this view
• Nausea and vomiting
• Hypersalivation: excessive saliva production

Prevention of Emergence Reactions

To reduce psychological side effects during recovery, ketamine is often combined with benzodiazepines (e.g., midazolam).

Contraindications

Ketamine should be used with caution or avoided in patients with:

• Known hypersensitivity to the substance
• Uncontrolled high blood pressure or severe cardiac disease
• Uncontrolled hyperthyroidism (overactive thyroid)
• Psychiatric conditions with a risk of psychosis (relative contraindication)

Abuse Potential and Legal Classification

Ketamine has a known potential for misuse and is sometimes used as a recreational drug. Chronic misuse can lead to severe bladder and kidney damage (known as ketamine-induced uropathy) as well as psychological dependence. In many countries, ketamine is classified as a controlled substance and may only be prescribed under strict regulations.

References

1. World Health Organization (WHO): Model List of Essential Medicines, 23rd Edition, 2023. Available at: https://www.who.int/publications/i/item/WHO-MHP-HPS-EML-2023.02
2. Kurdi MS, Theerth KA, Deva RS: Ketamine: Current applications in anesthesia, pain, and critical care. Anesthesia Essays and Researches, 2014;8(3):283-290. DOI: 10.4103/0259-1162.143110
3. Domino EF: Taming the ketamine tiger. Anesthesiology, 2010;113(3):678-684. DOI: 10.1097/ALN.0b013e3181ed09a2