Doses and Routes of Administration
Ketamine has been administered intravenously, intramuscularly,
orally, nasally, rectally, and as a preservative-free solution epidurally.[562]
Most clinical use involves the intravenous and intramuscular routes, by which the
drug rapidly achieves therapeutic levels. The dose depends on the desired therapeutic
effect and the route of administration. Table
10-11
contains the general recommended doses for intravenous and intramuscular
administration of ketamine for various therapeutic goals.[444]
Because of their side effects, most anesthetic drugs require that the dosage be
reduced in elderly and seriously ill patients; such a recommendation is probably
prudent with ketamine, although data supporting this recommendation are not available.
Patients who have been critically ill for a prolonged period may have exhausted
their catecholamine stores and may be subject to the circulatory depressant effects
of ketamine.[563]
Ketamine can be given epidurally
and intrathecally for operative and postoperative pain control. An intrathecal dose
of 1 mg ketamine combined with 0.15 to 0.2 mg of intrathecal morphine provided effective
cancer pain relief compared with 0.4 mg of intrathecal morphine alone. S-(+)-ketamine
(0.5 mg/kg) has also been combined with bupivacaine to enhance the duration of analgesia.
[565]
The peak action after intravenous administration
occurs in 30 to 60 seconds. Onset occurs in about 5 minutes, with peak effect occurring
approximately 20 minutes after intramuscular administration. An oral dose of 3 to
10 mg/kg generates a sedative effect in 20 to 45 minutes. Continuous infusion of
intravenous ketamine with or without concomitant drugs is a satisfactory method to
keep blood levels in the therapeutic range (see also Chapter
12
). The concomitant use of drugs such as benzodiazepines permits a lower
dose requirement for ketamine while enhancing recovery by reducing emergence reactions.
The interaction of ketamine with propofol is strictly additive and not synergistic;
thus, the dose of each would be reduced by about half when used together for induction.
[566]
For sedation, ketamine may be given intramuscularly if the patient
wishes to avoid awareness of intravenous catheter placement. It has also been administered
orally in doses of 3 to 10 mg/kg, with 6 mg/kg providing optimal conditions in 20
to 25 minutes in one study and 10 mg/kg providing sedation in 87% of children within
45 minutes in another study.[567]
[568]
In at least one case, deep sleep was produced by a supposedly sedative oral dose.
[569]
