G-Ketamine

Ketamine is commonly used for short-term anesthetic procedures in many animal species.

Ketamine is contraindicated in patients who have exhibited prior hypersensitivity reactions to it and animals to be used for human consumption.
Use in patients with significant hypertension, heart failure, and arterial aneurysms could be hazardous. The manufacturer warns against its use in patients with hepatic or renal insufficiency but in humans with renal insufficiency, the duration of action is not prolonged. Because ketamine does not provide good muscle relaxation, it is contraindicated when used alone for major surgery.
Ketamine can cause increases in CSF pressure and it should not be used in cases with elevated pressures or when head trauma has occurred. Because of its supposed epileptogenic potential, it should generally not be used (unless very cautiously) in animals with preexisting seizure disorders. As myelography can induce seizures, ketamine should be used cautiously in animals undergoing this procedure.
Ketamine is considered to be relatively contraindicated when increased intra-ocular pressure or open globe injuries exist, and for procedures involving the pharynx, larynx, or trachea. Animals that have lost significant amounts of blood, may require significantly reduced ketamine dosages.
While ketamine has been used safely in humans with malignant hyperthermia, its use in animals susceptible to this condition is controversial.
Ketamine can increase heart rate, increase blood pressure and myocardial oxygen consumption; its use should be avoided in cats with hypertrophic cardiomyopathy (HCM) or in other patients where an increase in heart rate, blood pressure and myocardial oxygen consumption can be detrimental (e.g., unstable shock or congestive heart failure). Its effects on respiratory function may be enhanced in patients with unstable cardiopulmonary function. Because of ketamine’s tendencies to increase sympathetic tone (increased norepinephrine release), it should be used with caution in animals where increased sympathetic tone concurrently exists (e.g., pheochromocytoma, hyperthyroidism). Hyperthyroid human patients (and those receiving exogenous thyroid replacement) may be susceptible to developing severe hypertension and tachycardia when given ketamine. The veterinary significance of this potential problem is unknown. Cats’ eyes remain open after receiving ketamine, and should be protected from injury plus an ophthalmic lubricant (e.g., Lacri-Lube®) should be applied to prevent excessive drying of the cornea.
Because ketamine is excreted almost exclusively via renal mechanisms, it should be used with caution in cats with reduced renal function. To minimize the incidences of emergence reactions, it is recommended to minimize exposure to handling or loud noises during the recovery period. The monitoring of vital signs should still be performed during the recovery phase, however.
Because ketamine can increase blood pressure, careful control of postsurgical hemorrhage (e.g., declawing) should be managed. It is not essential to withhold food or water prior to surgery, but in elective procedures, it is recommended to withhold food for 6 hours prior to surgery.

Ketamine is a widely used anesthetic agent. The precise mechanism of action is not known, but most evidence supports its action as a centrally acting dissociative agent. Ketamine produces mild analgesia and modulates pain via its ability to act as a noncompetitive antagonist for N-methyl D-aspartate (NMDA) receptors.
Ketamine is an equal concentration of two isomers (R-ketamine and S-ketamine). S-ketamine is more active and is eliminated faster. The S-isomer, called esketamine hydrochloride (Spravato), is an intranasal product that has been used in humans for treatment of depression. The mechanism by which it exerts its antidepressant effect is unknown. The major circulating metabolite noresketamine demonstrated activity at the same receptor with less affinity.
Pharmacokinetics: Ketamine is not active orally. It must be injected by IV, IM, or SQ routes. It has a short half-life in most animals (60–90 minutes) and is rapidly metabolized. The metabolite (norketamine) may produce more prolonged NMDA antagonistic effects but with less affinity for the receptor.

The following drug interactions have either been reported or are theoretical in humans or animals receiving ketamine and may be of significance in veterinary patients:
CHLORAMPHENICOL (parenteral): May prolong the anesthetic actions of ketamine
CNS DEPRESSANTS: Narcotics, barbiturates, or diazepam may prolong the recovery time after ketamine anesthesia
HALOTHANE: When used with halothane, ketamine recovery rates may be prolonged and the cardiac stimulatory effects of ketamine may be inhibited; close monitoring of cardiac status is recommended when using ketamine with halothane
IVERMECTIN: It has been recommended not to use ivermectin in reptiles within 10 days of ketamine (Bays 2009)
NEUROMUSCULAR BLOCKERS (e.g., succinylcholine and tubocurarine): May cause enhanced or prolonged respiratory depression
THYROID HORMONES: When given concomitantly with ketamine, thyroid hormones have induced hypertension and tachycardia in humans; betablockers (e.g., propranolol) may be of benefit in treating these effects

Ketamine causes pain with IM injection (pH of solution is 3.5). Tremors, muscle spasticity, and convulsive seizures have been reported. Spontaneous movements, salivation, and increased body temperature are more common in dogs when high doses are used. Ketamine increases sympathetic tone, heart rate, and blood pressure. It produces an increased cardiac output compared with other anesthetic agents. Salivation, mydriasis, and regurgitation are increased in animals that receive ketamine, which may be reduced by premedication within atropine. Apnea may develop in some animals, and oxygen supplementation should be available. Prolonged infusions in horses may delay GI transit times.

Hypertension, hypersalivation, respiratory depression, hyperthermia, emesis, vocalization, erratic & prolonged recovery, dyspnea, spastic jerking movements, seizures, muscular tremors, hypertonicity, opisthotonos, & cardiac arrest; pain after IM injection may occur Cats’ eyes remain open

Ketamine is considered to have a wide therapeutic index (approximately 5 times greater when compared to pentobarbital). When given too rapidly or in excessive doses, significant respiratory depression may occur. Treatment using mechanically assisted respiratory support is recommended versus the use of analeptic agents. In cats, yohimbine with 4-aminopyridine has been suggested for use as a partial antagonist

In humans, the FDA categorizes this drug as category C for use during pregnancy (Animal studies have shown an adverse effect on the fetus, but there are no adequate studies in humans; or there are no animal reproduction studies and no adequate studies in humans.) In a separate system evaluating the safety of drugs in canine and feline pregnancy (Papich 1989), this drug is categorized as class: B (Safe for use if used cautiously.
Studies in laboratory animals may have uncovered some risk, but these drugs appear to be safe in dogs and cats or these drugs are safe if they are not administered when the animal is near term.) No specific lactation information was found.

Ketamine injection should be stored between 15–30°C (59–86°F) and protected from light.

Solution may darken upon prolonged exposure to light which does not affect the drug’s potency. Do not use if precipitates appear.