Description and indication for use
Phenobarbitone is a long-acting barbiturate
with sedative hypnotic and anti-convulsant properties. It is used in the management of seizures.
Dose
Loading
dose:
20 mg – 40 mg/kg. ** (If ventilated, repeat doses of 10 – 15
mg/kg up to 100 mg/kg in 24 hours may be administered).
Maintenance:
3 – 5 mg/kg/day once daily or in 2 divided
doses. Adjust according to levels. Commence 24 hrs after loading dose.
Reconstitution/Dilution
Ampoule = 200 mg in 1 mL or 20 mg in 0.5 mL.
IV:
* Dilute to 100 mg/mL with Sodium Chloride
0.9%.
(Withdraw 1 mL of 200 mg/mL solution and
add to 1 mL of water for injections in a 2 mL syringe = 200 mg/2 mL = 100 mg/mL).
Discard excess volume to obtain required
dose or withdraw dose using another syringe.
IM:
Use 200 mg/mL undiluted.
Route and method of administration
iv:
Give at 1 mg/kg/minute or slower (maximum
IV push rate in an emergency 2 mg/kg/minute).
Loading dose over 30 minutes.
Side effects
Drowsiness.
Respiratory depression, apnoea.
Thrombophlebitis.
Hypotension.
Hepatitis, cholestasis.
Note: Injection contains Propylene Glycol 90% and Benzyl Alcohol 10 mg/mL.
Compatible Solutions
Glucose 5% and 10%.
Sodium Chloride 0.9%.
Incompatibilities
Phenobarbitone must not be mixed together
with the following drugs: Most antibiotics, Morphine, Noradrenaline, Phenytoin Sodium.
Avoid mixing with other drugs - flush
before and after with Sodium Chloride 0.9%.
Special precautions
CAUTION in patients with severe hepatic or renal impairment.
CAUTION in patients with hypotension or respiratory depression.
Half-life of Phenobarbitone may be prolonged
in patients with asphyxia.
Greater than 20 mg/kg/dose in neonates may
require mechanical ventilation.
Drug interactions
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Phenobarbitone
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May alter the effect of many drugs as it
stimulates liver microsomal enzyme production resulting in reduced serum
levels.
Drugs it may affect include Theophylline, Metronidazole
and Dexamethasone.
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Phenytoin
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Levels may be increased when given concurrently
with Phenytoin. Monitor serum levels of both drugs.
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Paracetamol
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Do not give high doses if giving Phenobarbitone.
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Chloramphenicol
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May have its effectiveness reduced and, in turn,
reduce the effectiveness of Phenobarbitone.
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Rifampicin
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May reduce effectiveness of Phenobarbitone.
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Nursing responsibilities
Cardiorespiratory monitor
Apply pulse oxymeter +/- transcutaneous CO2
monitor.
Check serum levels prn (therapeutic levels
= 80 – 120 micromol/L).
Observe IV site for signs of extravasation
and phlebitis.
Sampling time for levels immediately before the next
dose.