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P A R T 4
Drugs acting on the central and peripheral nervous systems
Clinically important drug–drug interactions
Caution must be used when barbituates are used with
any other CNS suppressants. They can cause decreased
effectiveness of theophylline, oral anticoagulants,
beta-blockers, corticosteroids, hormonal contraceptives,
phenylbutazones, metronidazole, quinidine and carba-
mazepine. Combinations of barbiturate anaesthetics
and opioids may produce apnoea more commonly than
occurs with other analgesics.
N
on
-
barbiturate anaesthetics
The other parenteral drugs used for intravenous admin-
istration in anaesthesia are non-barbiturates with a wide
variety of effects. Such anaesthetics include droperidol
(
Droleptan
), ketamine (
Ketalar
), midazolam (
Hypnovel
)
and propofol (
Diprivan
). (See Table 27.1.)
Therapeutic action and indications
Midazolam is the prototype non-barbiturate anaesthetic.
It is a very potent amnesiac. These drugs are thought to
act in the reticular activating system (RAS) and limbic
system to potentiate the effects of gamma-aminobutyric
acid (GABA). Midazolam’s amnesiac effects occur at
doses below those needed to cause sedation. It is widely
used to produce amnesia or sedation for many diagnos-
tic, therapeutic and endoscopic procedures. Midazolam
can also be used to induce anaesthesia and to provide
continuous sedation for intubated and people being
mechanically ventilated. Droperidol produces marked
TABLE 27.1
DRUGS IN FOCUS General anaesthetic agents
Drug name
Systems alert
a
Onset
Recovery Analgesia CV Resp CNS GI
Renal Hepatic
Barbiturate anaesthetics
thiopentone
(Pentothal)
10–30 seconds 3–8 minutes
none
— — — — — —
Non-barbiturate general anaesthetics
droperidol
(Droleptan)
3–10 minutes
2–4 hours
— ++
— +
— +
+
ketamine
(Ketalar)
30 seconds
45 minutes
+
++
— +++ — — —
midazolam
(Hypnovel)
15 minutes
30 minutes
+
— +++ — ++
— —
propofol
(Diprivan,
Fresofol,
Provive)
30–60 seconds 25–10 minutes
+
++
+
++
— — —
Anaesthetic gases
ethylene (red)
1–2 minutes
rapid
— — — +
+
— —
nitrous
oxide (blue)
1–2 minutes
rapid
++++
+++ +
+
— — —
Volatile liquids
desflurane
(Suprane)
1–2 minutes 15–20 minutes
+
— ++++ — — — —
isoflurane
(Aerrane,
Forthane)
1–2 minutes 15–20 minutes
+
++
+
— +
— —
methoxyflurane
(Penthrox)
10–30 seconds
rapid
++++
+
+
+
+
++
++
sevoflurane
(Sevorane)
30 seconds
10 minutes
+
— ++
— — — —
a
Systems alert indicates physiological systems with anticipated adverse effects to these drugs. When drugs are selected, the individual’s condition and
potential for serious problems with these adverse effects should be considered.
—, no effect; +, mild effect, ++, moderate effect; +++, strong effect; ++++, powerful effect
