Ketamine

Information from Zoetis:

CAUTION Federal law restricts this drug to use by or on the order of a licensed veterinarian. 

DESCRIPTION Ketamine (ketamine hydrochloride injection) is a rapidacting, nonnarcotic, nonbarbiturate agent for anesthetic use in cats and for restraint in subhuman primates. It is chemically designated dl 2-(ochlorophenyl)- 2-(methylamino) cyclohexanone hydrochloride and is supplied as a slightly acid (pH 3.5 to 5.5) solution for intramuscular injection in a concentration containing the equivalent of 100 mg ketamine base per milliliter and contains not more than 0.1 mg/mL benzethonium chloride as a preservative. 

INDICATIONS Ketamine may be used in cats for restraint or as the sole anesthetic agent for diagnostic or minor, brief, surgical procedures that do not require skeletal muscle relaxation. It may be used in subhuman primates for restraint.

CONTRAINDICATIONS Ketamine is contraindicated in cats and subhuman primates suffering from renal or hepatic insufficiency. Ketamine is detoxified by the liver and excreted by the kidneys; therefore, any preexistent hepatic or renal pathology or impairment of function can be expected to result in prolonged anesthesia; related fatalities have been reported. 

PRECAUTIONS In cats, doses in excess of 50 mg/kg during any single procedure should not be used. The maximum recommended dose in subhuman primates is 40 mg/kg. To reduce the incidence of emergence reactions, animals should not be stimulated by sound or handling during the recovery period. However, this does not preclude the monitoring of vital signs. Apnea, respiratory arrest, cardiac arrest and death have occasionally been reported with ketamine used alone, and more frequently when used in conjunction with sedatives or other anesthetics. Close monitoring of patients is strongly advised during induction, maintenance and recovery from anesthesia. Color of solution may vary from colorless to very slightly yellowish and may darken upon prolonged exposure to light. This darkening does not affect potency. Do not use if precipitate appears. 

ADVERSE REACTIONS Respiratory depression may occur following administration of high doses of ketamine (ketamine hydrochloride injection). If at any time respiration becomes excessively depressed and the animal becomes cyanotic, resuscitative measures should be instituted promptly. Adequate pulmonary ventilation using either oxygen or room air is recommended as a resuscitative measure. Adverse reactions reported have included emesis, salivation, vocalization, erratic recovery and prolonged recovery, spastic jerking movements, convulsions, muscular tremors, hypertonicity, opisthotonos, dyspnea and cardiac arrest. In the cat, myoclonic jerking and/or mild tonic convulsions can be controlled by ultrashort-acting barbiturates which should be given to effect. The barbiturates should be administered intravenously at a dose level of one-sixth to one-fourth the usual dose for the product being used. Acepromazine may also be used. However, recent information indicates that some phenothiazine derivatives may potentiate the toxic effects of organic phosphate compounds such as found in flea collars and certain anthelmintics. A study has indicated that ketamine hydrochloride alone does not potentiate the toxic effects of organic phosphate compounds. To report suspected adverse reactions, to obtain a Material Safety Data Sheet or for technical assistance, call 1-888-963-8471. 

ACTION Ketamine is a rapid-acting agent whose pharmacological action is characterized by profound analgesia, normal pharyngeal-laryngeal reflexes, mild cardiac stimulation and respiratory depression. Skeletal muscle tone is variable and may be normal, enhanced or diminished. The anesthetic state produced does not fit into the conventional classification of stages of anesthesia, but instead ketamine produces a state of unconsciousness which has been termed “dissociative” anesthesia in that it appears to selectively interrupt association pathways to the brain before producing somesthetic sensory blockade. In contrast to other anesthetics, protective reflexes, such as coughing and swallowing are maintained under ketamine anesthesia. The degree of muscle tone is dependent upon level of dose; therefore, variations in body temperature may occur. At low dosage levels there may be an increase in muscle tone and a concomitant slight increase in body temperature. However, at high dosage levels there is some diminution in muscle tone and a resultant decrease in body temperature, to the point where supplemental heat may be advisable. In cats, there is usually some transient cardiovascular stimulation, increased cardiac output with slight increase in mean systolic pressure with little or no change in total peripheral resistance. At higher doses the respiratory rate is usually decreased. The assurance of a patent airway is greatly enhanced by virtue of maintained pharyngeal-laryngeal reflexes. Although some salivation is occasionally noted, the persistence of the swallowing reflex aids in minimizing the hazards associated with ptyalism. Salivation may be effectively controlled with atropine sulfate in dosages of 0.04 mg/kg (0.02 mg/lb) in cats and 0.01 to 0.05 mg/kg (0.005 to 0.025 mg/lb) in subhuman primates. Other reflexes, e.g., corneal, pedal, etc., are maintained during ketamine (ketamine hydrochloride injection) anesthesia, and should not be used as criteria for judging depth of anesthesia. The eyes normally remain open with the pupils dilated. It is suggested that a bland ophthalmic ointment be applied to the cornea if anesthesia is to be prolonged. Following administration of recommended doses, cats become ataxic in about 5 minutes with anesthesia usually lasting from 30 to 45 minutes at higher doses. At the lower doses, complete recovery usually occurs in 4 to 5 hours but with higher doses recovery time is more prolonged and may be as long as 24 hours. Recovery is generally smooth and uneventful. The duration is dose related. By single intramuscular injection, ketamine usually has a wide margin of safety in cats and subhuman primates. In cats, cases of prolonged recovery and death have been reported.

Information from Plumb's Veterinary Drug Handbook, 7th Edition, by Donald C. Plumb:

Contraindications: Ketamine is contraindicated in patients who have exhibited prior hypersensitivity reactions; who have significant hypertension, heart failure, or arterial aneurysms; and when used alone for major surgery, since it does not provide good muscle relaxation. Use with caution in patients with hepatic or renal insufficiency. It can cause increased CSF pressure and should not be used in cases with elevated pressures or head trauma. Due to its epileptogenic properties, it should be not be used in patients with preexisting seizure disorders, or patients undergoing myelography. Ketamine is relatively contraindicated in cases with increased intraocular pressure or open globe injuries; or procedures involving the pharynx, larynx, or trachea. Animals with significant blood loss need significantly reduced dosing. Use of ketamine in animals with malignant hyperthermia is controversial and not advised. Ketamine should be avoided for patients in which elevated heart rate, blood pressure, and myocardial oxygen consumption would be detrimental (i.e. HCM, unstable shock, congestive heart failure). Due to its tendency to increase norepinephrine release and sympathetic tone, it should be used with caution in patients where increased sympathetic tone currently exists (i.e. pheochromocytoma, hyperthyroidism. 

Adverse effects: Possible adverse effects include respiratory depression, emesis, vocalization, erratic or prolonged recovery, dyspnea, spastic jerking movements, convulsions, muscular tremors, hypertonicity, opisthotonos, seizures, and cardiac arrest. Pain after IM injection may occur. To reduce autonomic signs like hypersalivation, atropine or glycopyrrolate can be administered. 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; however, in cats, yohimbine has been suggested for use as a partial agonist.

Ketamine may have interactions with the following drugs: chloramphenicol, CNS depressants, halothane, ivermectin, neuromuscular blockers, thyroid hormones.