Posology : מינונים

4.2      Posology and method of administration

Preoperative preparations
While vomiting has been reported following ketamine administration, some airway protection may be afforded because of active laryngeal-pharyngeal reflexes.
However, since aspiration may occur with ketamine and since protective reflexes may also be diminished by supplementary anesthetics and muscle relaxants, the possibility of aspiration must be considered. Ketamine is recommended for use in the patient whose stomach is not empty when, in the judgment of the practitioner, the benefits of the drug outweigh the possible risks.
Premedications with an anticholinergic agent (e.g., atropine, scopolamine, hyoscine, or glycopyrrolate) or another drying agent should be given at an appropriate interval prior to induction to reduce ketalar-induced hypersalivation.
Midazolam, diazepam, lorazepam, or flunitrazepam used as a premedicant or as an adjunct to ketamine, have been effective in reducing the incidence of emergence reactions.
Onset and duration
Because of rapid induction following intravenous injection, the patient should be in a supported position during administration.
The onset of action of ketamine is rapid; an intravenous dose of 2 mg/kg of body weight usually produces surgical anaesthesia within 30 seconds after injection and the anaesthetic effect usually lasts 5 to 10 minutes. If a longer effect is desired, additional increments can be administered intravenously or intramuscularly to maintain anesthesia without producing significant cumulative effects.


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Intramuscular doses, from experience primarily in pediatric patients, in a range of 9 mg/kg to 13 mg/kg usually produce surgical anesthesia within 3 to 4 minutes following injection, with the anesthetic effect usually lasting 12 to 25 minutes.
Dosage:
As with other general anesthetic agents, the individual response to ketamine 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 against the patient's requirements.
Supplementary Agents:
Ketamine is clinically compatible with the commonly used general and local anesthetic agents when an adequate respiratory exchange is maintained.
The regimen of a reduced dose of ketamine supplemented with diazepam can be used to produce balanced anesthesia by combination with other agents such as nitrous oxide and oxygen.

General Anesthesia Induction

Intravenous Route:
Adults: The initial dose of Ketamine administered intravenously may range from 1 mg/kg to 4.5mg/kg. The average amount required to produce 5 to 10 minutes of surgical anaesthesia has been 2.0 mg/kg.
Alternatively, in adult patients an induction dose of 1.0 mg to 2.0 mg/kg intravenous ketamine at a rate of 0.5 mg/kg/min may be used for induction of anesthesia. In addition, diazepam in 2 mg to 5 mg doses, administered in a separate syringe over 60 seconds, may be used. In most cases, 15 mg of intravenous diazepam or less will suffice. The incidence of psychological manifestations during emergence, particularly dream-like observations and emergence delirium, may be reduced by this induction dosage program.
Rate of Administration: It is recommended that ketamine be administered slowly (over a period of 60 seconds). More rapid administration may result in respiratory depression and enhanced pressor response.

Intramuscular Route:
Adults: The initial dose of ketamine administered intramuscularly may range from 6.5 mg/kg to 13 mg/kg. A dose of 10 mg/kg will usually produce 12 to 25 minutes of surgical anaesthesia.
Dosage in Hepatic Insufficiency:
Dose reductions should be considered in patients with cirrhosis or other types of liver impairment (see section 4.4 Special warnings and Precautions for Use – General).

Maintenance of General Anaesthesia
The maintenance dose should be adjusted according to the patient's anesthetic needs and whether an additional anesthetic agent is employed.
Increments of one-half to the full induction dose may be repeated as needed for maintenance of anesthesia. However, it should be noted that purposeless and tonic- clonic 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 

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doses of the anesthetic. It should be recognized that the larger the total dose of ketamine administered, the longer will be the time to complete recovery.
Adult patients induced with ketamine augmented with intravenous diazepam may be maintained on ketamine given by slow microdrip infusion technique at a dose 0.1 mg/minute to 0.5 mg/minute, augmented with diazepam 2 to 5 mg administered intravenously as needed. In many cases 20 mg or less of intravenous diazepam total for combined induction and maintenance will suffice. However, slightly more diazepam may be required depending on the nature and duration of the operation, physical status of the patient, and other factors. The incidence of psychological manifestations during emergence, particularly dream-like observations and emergence delirium, may be reduced by this maintenance dosage program.