DATE OF PREPARATION July 5, 2005
DATE OF REVISION
Control No. 099611
Parenteral General Anesthetic
KETALAR, dl 2-(o-chlorophenyl)-2-(methylamino) cyclohexanone hydrochloride, is a white crystalline compound, soluble in water to 20% clear and colorless solution. Aqueous solutions in use have pH range from 3.5 to 5.5. The base component is 86.7% of the salt. It is supplied as a slightly acidic (pH 3.5 - 5.5) solution for intravenous or intramuscular injection in concentrations containing the equivalent of either 10 to 50 mg ketamine base per mL and contains 0.01% Phemerol (benzethonium chloride) as a preservative. The 10 mg per mL solution has been made isotonic with sodium chloride.
KETALAR is a rapid-acting, nonbarbiturate general anesthetic. It produces an anesthetic state characterized by profound analgesia, normal pharyngeal-laryngeal reflexes and normal or slightly enhanced skeletal muscle tone. Mild cardiac stimulation and occasionally respiratory depression occur. The anesthetic state produced by KETALAR has been termed "dissociative anesthesia" in that it appears to selectively interrupt association pathways of the brain before producing somesthetic sensory blockage. KETALAR decreases the activity of the neocortex and subcortical structures (thalamus) and increases the activity in the limbic system and reticular substance. Following administration of recommended doses of KETALAR, blood pressure and pulse rate are usually moderately and temporarily increased. In 12,283 procedures, the median systolic rise was 24% and the median diastolic rise was 22%. Respiration is usually unaffected. Mild stimulation occasionally occurs. However, transient respiratory depression (rate and tidal volume) may occur and is generally associated with rapid (less than 60 seconds) intravenous administration. Blood gas tensions (PO2 and PCO2) are relatively unaffected. A patent airway is maintained partly by virtue of unimpaired pharyngeal and laryngeal reflexes. Ketamine undergoes N-demethylation and hydroxylation of the cyclohexanone ring, with the formation of water-soluble conjugates which are excreted in the urine. Further oxidation also occurs with the formation of a cyclohexanone derivative. The unconjugated N-demethylated metabolite was found to be less than one sixth as potent as ketamine. The unconjugated demethyl cyclohexanone derivative was found to be less than one tenth as potent as ketamine. Studies in human subjects resulted in the mean recovery of 91% of the dose in the urine and 3% in the feces. Peak plasma levels averaged about 0.75 ug/mL and CSF levels were about 0.2
u
g/mL, 1 hour after dosing.
As the sole anesthetic agent for recommended diagnostic and surgical procedures.
Although best suited to short procedures, KETALAR can be used, with additional doses, for longer procedures.
If skeletal muscle relaxation is desired, a muscle relaxant should be used. In surgical procedures involving visceral pain pathways, KETALAR should be supplemented with an agent which obtunds visceral pain.
For the induction of anesthesia
prior to the administration of other general anesthetic agents.
To supplement low potency agents
such as nitrous oxide. Specific areas of application or types of procedures have included:
Neurodiagnostic procedures such as pneumoencephalograms, ventriculograms, myelograms, and lumbar punctures.
Diagnostic and operative procedures of the eye, ear, nose and mouth. Eye movements may persist during ophthalmological procedures. Before KETALAR can be recommended for intraocular surgery, more data are required.
Diagnostic and operative procedures of the pharynx, larynx or bronchial tree.
Adequate muscle relaxants must be used in such procedures (see Contraindications and Precautions).
Sigmoidoscopy and minor surgery of the anus and rectum, and circumcision. Extraperitoneal procedures used in gynecology such as dilation and curettage. More data are required before KETALAR can be recommended for use in obstetrical delivery or cesarean section (see Warnings and Precautions). Orthopedic procedures such as closed reductions, manipulations, femoral pinning, amputations, and biopsies. Dental extractions. Miscellaneous procedures of general surgery such as debridement, painful dressings, and skin grafting in burn patients. Anesthesia in poor-risk patients where depression of vital functions precludes the use of other general anesthetics. In procedures where the intramuscular route of administration is preferred.
The drug is contraindicated in persons with a history of cerebrovascular accident. It is contraindicated in those in whom a significant elevation of blood pressure would constitute a serious hazard, such as patients with significant hypertension. It is contraindicated in persons with severe cardiac decompensation. It is contraindicated in surgery of the pharynx, larynx, or bronchial tree unless adequate muscle relaxants are used. It is contraindicated in those showing hypersensitivity to the drug.
KETALAR is for use only by or under the direction of physicians experienced in administering general anesthetics and in maintenance of an airway and in the control of respiration.
Cardiac function should be continually monitored during the procedure in patients found to have hypertension or cardiac decompensation.
Barbiturates and KETALAR, being chemically incompatible because of precipitate formation, should not be injected from the same syringe.
Barbiturates and narcotics, being central nervous system depressants, may prolong recovery time if used concurrently with KETALAR.
Postoperative confusional states may occur during the recovery period (see item 5 under Precautions).
Respiratory depression may occur with overdosage or too rapid administration of KETALAR, in which case supportive ventilation should be employed. Mechanical support of respiration is preferred to administration of analeptics.
An increase in cerebrospinal fluid pressure has been reported following the administration of ketamine hydrochloride. Therefore, special caution should be exercised when using KETALAR in cases with pre-existing elevated intracranial pressure, and in those cases with normal intracranial pressure in which, in the opinion of the physician, a rise in such pressure would entail special risks. Use with extreme caution in patients with preanesthetic elevated cerebrospinal pressure.
Although animal studies of teratogenicity, fertility, and reproduction indicated the safety of KETALAR, its safe use in human pregnancy has not been established (see Precautions).
Because pharyngeal and laryngeal reflexes are usually active, ketamine should not be used alone in surgery or diagnostic procedures of the pharynx, larynx, or bronchial tree. Mechanical stimulation of the pharynx should be avoided, whenever possible if ketamine is used alone. Muscle relaxants with proper attention to respiration, may be required in both of these instances. Precautions should be used in patients with upper respiratory infection because of the increased danger of respiratory difficulties, such as laryngospasm, in these cases. Resuscitative equipment should be available and ready for use. The initial intravenous dose should be administered over a period of 60 seconds. More rapid administration may result in respiratory depression and enhanced pressor response. In surgical procedures involving visceral pain pathways, KETALAR should be supplemented with an agent which obtunds visceral pain. During recovery from anesthesia, the patient may go through a phase of emergence reaction characterized by vivid dreams, dream-like states, confusion (with or without psychomotor activity), excitement, delirium, irrational behavior and occasionally hallucinations. In some cases these states have been accompanied by confusion, excitement, and irrational behavior which a few patients recall as an unpleasant experience. The duration ordinarily is no more than a few hours; in a few cases, however, recurrences have taken place up to 24 hours postoperatively. No residual psychological effects are known to have resulted from the use of ketamine. In 12,283 procedures, post anesthetic emergence responses were broken down in the following parameters and the incidence of reaction was:
| Reaction | Number | Percent | Percent In 15 to 35 Yrs. Age Group |
| Dreams, Pleasant or Not Specified | 679 | 5.44 | 9.6 |
| Dreams, Unpleasant | 199 | 1.62 | 3.1 |
| Hallucinations | 152 | 1.23 | 1.6 |
| Confusion, With and Without Vocalization | 327 | 2.66 | 4.7 |
| Excitement or Irrational Behaviour | 111 | 0.89 | 1.8 |
| Psychic Abnormalities | 62 | 0.51 | 0.8 |
| Overall Rate t | 11.0 | 19.4 |
t
Some procedures have multiple emergence reactions, therefore the overall rate is less than the sum of the reactions.
As this table shows, the emergence reactions are more common in the 15 to 35 years group. The reactions tabled above occurred in the majority of instances in patients in whom droperidol or diazepam had not been used as premedications (see reference "Dosage and Administration"). The incidence of these emergence phenomena is least in the young (15 years of age or less) and elderly (over 65 years of age) patient. Also, they are less frequent when the drug is given intramusculary and the incidence is reduced as experience with the drug is gained. The incidence of psychological manifestations during emergence, particularly dream-like observations and emergence delirium, may be reduced by using lower recommended dosages of ketamine in conjunction with intravenous diazepam during induction and maintenance of anesthesia. The incidence of emergence reactions may be reduced if verbal, tactile and visual stimulation of the patient is avoided during the recovery period; and certainly until the patient is fully conscious and able to be returned to the ward. These precautions do not preclude the monitoring of vital signs. The use of hypnotic doses of ultrashort-acting thiobarbiturates (50-100 mg I.V.) can be used to terminate severe emergence reactions. Diazepam, 5 mg I.V. has also been used to terminate emergence reactions. Long-term follow-up observations of 221 patients (140 with KETALAR, 81 with other anesthetic agents) have not revealed any residual psychological effects. During anesthesia, the eyelids may remain retracted. During recovery, they close. Premature stimulation during recovery in the presence of nystagmus and diplopia may precipitate retching, nausea, or frank vomiting. Purposeless movements of extremities may occur during the course of anesthesia. These movements do not imply a light plane and are not indicative of the need for additional doses of the anesthetic. When ketamine is used on an outpatient basis, the patient should not be released until recovery from anesthesia is completed and then should be accompanied by a responsible adult. Use with caution in the chronic alcoholic and the acutely alcohol-intoxicated patient.
Pregnancy
In obstetrics, with the exception of administration during abdominal delivery or vaginal delivery, no controlled clinical studies have been conducted. The safe use in pregnancy has not been established, and such use is not recommended.
Drug Interactions
Prolonged recovery time may occur if barbiturates and/or narcotics are used concurrently with ketamine. Ketamine is clinically compatible with the commonly used general and local anesthetic agents when an adequate respiratory exchange is maintained.
One of the most characteristic physiologic effects of KETALAR is temporary augmentation of the pulse rate and blood pressure. Elevation of blood pressure begins shortly after injection, reaches a maximum within a few minutes and usually returns to preanesthetic values within 15 minutes of injection. The median peak rise has ranged from 20 to 25% of preanesthetic values for both systolic and diastolic readings. Depending on the condition of the patient, this elevation of blood pressure may be considered a beneficial effect, or in others, an adverse reaction. If elevation of blood pressure would be considered adverse to the patient, the benefit to risk ratio should be carefully determined (see Contraindications). Maintaining or moderately increasing blood pressure may be beneficial to some patients, as those in shock or those in whom reduction in blood pressure is contraindicated (see Warnings). Hypotension, arrhythmias, and bradycardia have been occasionally observed. Although respiration is frequently stimulated, severe depression of respiration or apnea may occur following rapid intravenous administration of high doses of ketamine. Respiratory depression, mild or moderate and transient, occurred in a small percentage of patients with normal doses. In the majority of these patients, it is not a serious problem. Laryngospasm and other forms of airway obstruction have occurred during KETALAR anesthesia. Increased salivation may occur unless an antisialagogue is used. In some patients, enhanced skeletal muscle tone may be manifested by tonic and clonic movements, sometimes resembling seizures. These movements do not imply a light plane and are not indicative of the need for additional doses of the anesthetic. EEG recordings were made in 14 patients receiving KETALAR. Although one of these patients exhibited slight twitching of the arms and legs, none showed EEG changes to suggest seizure reactions. Epileptiform attacks have been observed in a few patients following KETALAR administration. However, KETALAR has been used successfully in patients known to be suffering from epilepsy. Blurred vision, nystagmus and diplopia are not uncommon findings during the recovery period. Anorexia, nausea or vomiting are minimal, allowing the great majority of patients to take liquids by mouth shortly after regaining consciousness. Except for occasional reports of local pain and exanthema at the injection site, KETALAR is well tolerated by the patient when administered either by the intravenous or intramuscular route. Transient erythema, morbilliform rash and anaphylaxis and have been reported. KETALAR causes a small transient increase in intraocular pressure. However, it has been used in patients with glaucoma without causing any deterioration in this condition.
Ketamine has been reported being used as a drug of abuse. Reports suggest that ketamine produces a variety of symptoms including, but not limited to, flashbacks, hallucinations, dysphoria, anxiety, insomnia, or disorientation. Ketamine dependence and tolerance may develop in individuals with a history of drug abuse or dependence. Therefore, ketamine should be prescribed and administered with caution.
Respiratory depression can result from an overdosage or too rapid a rate of administration of KETALAR. Supportive ventilation should be employed. Mechanical support of respiration that will maintain adequate blood oxygen saturation and carbon dioxide elimination is preferred to administration of analeptics. Ketamine has a wide margin of safety; several instances of unintentional administration of overdoses of KETALAR (up to ten times of the usually required dose) have been followed by prolonged but complete recovery.
KETALAR is a cataleptic, analgesic and anesthetic agent devoid of sedative or hypnotic properties, distinguishing it from the commonly used barbiturates. The depth of analgesia and anesthesia induced by KETALAR varies with the animal species, being more pronounced in monkeys, cats, rats and mice than in pigeons, guinea pigs, dogs and rabbits. Metabolism: KETALAR is rapidly absorbed following parenteral administration. Animal experiments indicated that KETALAR was rapidly distributed into body tissues, with relatively high concentrations appearing in body fat, liver, lung and brain; lower concentration were found in the heart, skeletal muscle and blood plasma. Placental transfer of the drug was found to occur in pregnant dogs and monkeys. No significant degree of blinding to serum albumin was found with KETALAR. Balance studies in rats, dogs, and monkeys resulting in the recovery of 85 to 95% of the dose in the urine, mainly in the form of degradation products. Small amounts of drug were also excreted in the bile and feces. Balance studies with tritium-labelled KETALAR in human subjects (1 mg/lb given intravenously) resulted in the mean recovery of 91% of the dose in the urine and 3% in the feces. Peak plasma levels averaged about 0.75 ug/mL, and CSF levels were about 0.2 ug/mL, one hour after dosing. KETALAR undergoes N-demethylation and hydroxylation of the cyclohexanone ring, with the formation of water-soluble conjugates which are excreted in the urine. Further oxidation also occurs with formation of a cyclohexanone derivative. The unconjugated N-demethylated metabolite was found to be less than one-sixth as potent as KETALAR. The unconjugated demethyl cyclohexanone derivative was found to be less than one-tenth as potent as KETALAR. Repeated doses of KETALAR administered to animals did not produce any detectable increase in microsomal enzyme activity. Doses of 0.5 to 2.0 mg/kg of KETALAR produce consistent and marked changes of EEG in man. The abolition of alpha waves and induction of theta activity were the most typical effects of KETALAR.
The intraperitoneal LD50 values were 275 mg/kg in neonatal mice, 209 mg/kg in preweaning mice, and 224 mg/kg in adult mice. In rats, the intraperitoneal LD50 values were 146 mg/kg for the neonates, 170 mg/kg for the preweaning groups, and 224 mg/kg for adult rats.
There was no evidence of drug related local damage when KETALAR was given by intravenous or intra-arterial routes to rats or dogs.
Rats given daily I.V. injections of 2.5 to 10 mg/kg of KETALAR for six weeks had only slight food intake depression and moderate weight gain depression, which was dose related in males but not in females. Regular monitoring of laboratory data and final autopsy studies failed to demonstrate drug-related toxic effects. Weight loss in dogs given daily I.M. injections of KETALAR up to 40 mg/kg for six weeks presumably was due to general depression of physical activity produced by the drug. There were no consistent hematologic or hematopoietic alterations. There were elevations in serum cholesterol, urea, alkaline phosphatase and transaminase values which were most prominent in animals receiving high doses. These values returned to normal levels at the termination of the dosing period. These altered values may be associated with temporary anorexia and weight loss. Histologic changes were not significant. When monkeys were anesthetized for three to six hours, twice weekly for four to six weeks, there were minor elevations in the sedimentation rate and variable changes in the total leukocyte and neutrophil differential values.
There were no apparent adverse effects on the dam or the pups when three groups of pregnant bitches were given 25 mg/kg of KETALAR I.M. twice a week over a three week period during first, second, and third trimester of pregnancy respectively. When rats were given KETALAR during the premating period, the period of organogenesis, and the perinatal period in doses from 10 mg to 20 mg/kg I.V. or I.M., the breeding performance and condition of the litters were not significantly different from the control animals injected with saline. Of inseminated rabbits given 20 mg/kg of KETALAR I.M., there were no drug induced effects on the litters during the period of organogenesis.
KETALAR has been safely used alone when the stomach was not empty. However, since the need to use supplementary anesthetic or muscle relaxant agents cannot always be predicted, it is preferable not to give anything by mouth for at least six hours before elective surgery. KETALAR is recommended for use in patients whose stomach is not empty when in the judgment of the physician the benefits of the drug outweigh the possible hazards.
Atropine, scopolamine, or other drying agents should be given at an appropriate interval prior to induction.
Certain drugs such as droperidol or diazepam intramuscularly have been used in an attempt to reduce the incidence of emergence reactions: sufficient data have not yet been accumulated to constitute thorough documentation. The incidence of emergence reactions is reduced as experience with the drug is gained.
As with other general anesthetic agents, the individual response to KETALAR is somewhat varied depending on the dose, route of administration, and age of patient, so that dosage recommendation cannot be absolutely fixed. The drug should be titrated to the patient's requirements.
Because of rapid induction following the initial intravenous injection, the patient should be in a supported position during administration. The onset of action of KETALAR is rapid; an intravenous dose of 1 mg/lb (2 mg/kg) of body weight usually produces surgical anesthesia within 30 seconds after injection, with the anesthetic effect usually lasting five to ten minutes. If a longer effect is desired, additional increments can be administered intravenously or intramuscularly to maintain anesthesia without producing significant cumulative effects. Intramuscular doses, from experience primarily in children, in a range of 4 to 6 mg/lb (9 to 13 mg/kg) usually produce surgical anesthesia within three to four minutes following injection, with the anesthetic effect usually lasting 12 to 25 minutes.
Intravenous Route:
The initial dose of KETALAR administered intravenously may range from 0.5 to 2 mg/lb (1.0/kg to 4.5 mg/kg). The average amount required to produce five to ten minutes of surgical anesthesia has been 1 mg/lb (2.0 mg/kg).
Rate of Administration
: It is recommended that KETALAR be administered slowly (over a period of 60 seconds). More rapid administration may result in respiratory depression and enhanced pressor response.
Intramuscular Route
: The initial dose of KETALAR administered intramuscularly may range from 3 to 6 mg/lb (6.5 - 13.0 mg/kg). A dose of 5 mg/lb (10 mg/kg) will usually produce 12 to 25 minutes of surgical anesthesia.
: Increments of 1/2 to the full induction dose, either intravenous or intramuscular may be repeated as needed for maintenance of anesthesia. Nystagmus, movements in response to stimulation, and vocalization may indicate lightening of anesthesia.
KETALAR is clinically compatible with the commonly used general and local anesthetic agents when an adequate respiratory exchange is maintained. When KETALAR is used as an induction agent, prior to the administration of other general anesthetic agents:
The full induction dose of KETALAR should be given I.V. over 60 seconds.
At the completion of the induction dose of KETALAR, the anesthetist should proceed immediately with the chosen general anesthetic procedure. A second dose of KETALAR (half the original induction dose) may be required at five to eight minutes following the initial induction dose when using an agent such as methoxyflurane where some considerable time is required for full surgical anesthesia to be established with the gaseous anesthetic. Otherwise, lightening in the depth of anesthesia may occur and the patient may enter the stage of excitement, associated with vocalization and purposeful movements.
Following the procedure, the patient should be observed but left undisturbed. This does not preclude the monitoring of vital signs.