1. Clinical Overview
Ketamine is a rapid-acting, non-barbiturate, phencyclidine derivative dissociative anesthetic agent. It is a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist. In the 10mg oral formulation, it is primarily used as an adjunctive treatment for treatment-resistant depression (TRD) and chronic neuropathic pain, under strict medical supervision. It produces a trance-like state providing pain relief, sedation, and amnesia. Its unique mechanism provides rapid antidepressant effects, often within hours, unlike conventional antidepressants.
| Onset | Duration | Bioavailability |
|---|---|---|
| Intravenous: 30 seconds; Intramuscular: 3-4 minutes; Oral: 20-30 minutes; Intranasal: 5-15 minutes. | Intravenous/Intramuscular anesthetic effect: 5-10 minutes (with full recovery in 1-2 hours). Oral antidepressant/analgesic effect: Variable, from hours to days depending on indication and regimen. | Intravenous: 100%; Intramuscular: 93%; Oral: ~17-20% (due to significant first-pass metabolism); Intranasal: ~25-50%. |
2. Mechanism of Action
Ketamine's primary mechanism is the non-competitive antagonism of the N-methyl-D-aspartate (NMDA) receptor, an ionotropic glutamate receptor. This blockade, particularly in the thalamo-neocortical and limbic systems, leads to a functional dissociation between the thalamus and the limbic cortex, producing a 'dissociative anesthetic' state. Its rapid antidepressant effect is believed to involve a cascade: NMDA receptor blockade on GABAergic interneurons leads to disinhibition of glutamatergic neurons, resulting in a surge of glutamate. This activates AMPA receptors, triggering downstream pathways (BDNF release, mTOR activation) that promote synaptogenesis and reverse the synaptic deficits associated with depression.
3. Indications & Uses
- Induction and maintenance of general anesthesia (parenteral form)
- Procedural sedation and analgesia (parenteral form)
4. Dosage & Administration
Adult Dosage: For Treatment-Resistant Depression (Oral/Sublingual, off-label): Typically 0.5 mg/kg to 1 mg/kg, administered 2-3 times per week initially. A 10mg dose is on the very low end and would be part of a titrated regimen, e.g., starting at 0.5 mg/kg (for a 70kg person = 35mg). Dosing is highly individualized. For Neuropathic Pain (Oral): 0.5 mg/kg to 1 mg/kg every 8-12 hours, titrated to effect. Maximum daily oral dose rarely exceeds 3 mg/kg/day.
Administration: Oral 10mg tablets are typically used off-label. They may be administered sublingually (placed under the tongue to dissolve) to improve bioavailability and reduce first-pass metabolism. Patient should not eat or drink for 15 minutes before and after sublingual administration. Administration must occur in a clinical setting where vital signs (BP, HR, SpO2) and mental state can be monitored for at least 2 hours post-dose. Patient MUST NOT drive or operate machinery for 24 hours.
5. Side Effects
Common side effects may include:
- Dizziness, vertigo
- Nystagmus (involuntary eye movements)
- Nausea, vomiting
- Diplopia (double vision)
- Sedation, drowsiness
- Euphoria or dysphoria
- Increased blood pressure and heart rate
- Perceptual disturbances (floating sensation)
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Theophylline, Aminophylline | Increased risk of seizures when used concurrently with ketamine. | Major |
| CNS Depressants (e.g., Alcohol, Benzodiazepines, Opioids, Barbiturates) | Additive CNS and respiratory depression. However, benzodiazepines (e.g., midazolam) are often used prophylactically to reduce emergence reactions. | Major |
| Sympathomimetics (e.g., Epinephrine, Dopamine) | Additive hypertensive and tachycardic effects. | Major |
| Thyroid Hormones | Increased risk of hypertension and tachycardia. | Moderate |
| CYP3A4 Inhibitors (e.g., Clarithromycin, Ketoconazole, Ritonavir) | Increase ketamine plasma levels, potentiating its effects and side effects. | Moderate |
| CYP3A4 Inducers (e.g., Rifampicin, Carbamazepine, Phenytoin) | Decrease ketamine plasma levels, potentially reducing efficacy. | Moderate |
| Neuromuscular Blocking Agents (e.g., Succinylcholine, Vecuronium) | Ketamine may potentiate their neuromuscular blocking effect. May increase risk of bradycardia with succinylcholine. | Moderate |
| Halothane | Increased risk of bradycardia, arrhythmias, and reduced cardiac output. | Major |
7. Patient Counselling
- DO take the medication exactly as prescribed by your specialist, in the clinical setting only.
- DO inform your doctor about all other medications, supplements, and herbal products you are taking.
- DO arrange for a responsible adult to accompany you home after the treatment session.
- DO report any history of substance abuse, psychiatric illness, or heart problems to your doctor.
- DONT drive, operate machinery, or engage in hazardous activities for at least 24 hours after a dose.
- DONT consume alcohol or any recreational drugs while on this treatment.
- DONT make any important decisions on the day of treatment due to potential cognitive impairment.
- DONT increase the dose or frequency without consulting your doctor.
8. Toxicology & Storage
Overdose: Manifestations are extensions of its pharmacological effects: Severe respiratory depression or apnea, cardiovascular collapse (hypotension or severe hypertension), arrhythmias, coma, prolonged dissociative state, severe psychosis, seizures, and increased intracranial pressure.
Storage: Store at controlled room temperature (15°C to 30°C). Protect from light and moisture. Keep in the original container, tightly closed. Due to its abuse potential, it must be stored in a locked cabinet, out of reach and sight of children and others. Dispose of unused medication as per pharmacy guidelines; do not flush or throw in household trash.