McKenna's Pharmacology for Nursing, 2e

420

P A R T 4  Drugs acting on the central and peripheral nervous systems

TABLE 27.1

DRUGS IN FOCUS General anaesthetic agents

Systems alert a

Drug name

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

+

++

— +++ — — —

15 minutes

30 minutes

+

— +++ — ++

— —

midazolam (Hypnovel)

propofol

30–60 seconds 25–10 minutes

+

++

+

++

— — —

(Diprivan, Fresofol, Provive)

Anaesthetic gases ethylene (red)

1–2 minutes 1–2 minutes

rapid rapid

— — — +

+

— —

++++

+++ +

+

— — —

nitrous oxide (blue)

Volatile liquids desflurane (Suprane)

1–2 minutes 15–20 minutes

+

— ++++ — — — —

1–2 minutes 15–20 minutes

+

++

+

— +

— —

isoflurane (Aerrane,

Forthane)

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

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