Phenobarbitone

Phenobarbitone

[1 ampoule $9.48; 1 tablet 20 cents]

ADMINISTRATION ROUTES:

  • IV, PO

ALTERNATIVE NAMES:

  • Phenobarbitone

ICU INDICATIONS:

  1. treatment of status epilepticus in children (in accordance with the Starship protocol)

PRESENTATION AND ADMINISTRATION:

  • IV:
    200mg in 1ml of phenobarbitone
    For direct IV injection, dilute dose to at least ten times its volume with water for injection. Inject slowly at a rate not exceeding 60mg/min. Dilute immediately before use. Do not store diluted solution. Do not use any solution that contains a precipitate or is more than slightly discoloured.
    May be given into side arm when any of the following fluids are being infused:
    0.9% sodium chloride, Hartmanns, 5% and 10% dextrose, glucose and sodium chloride
    Store at room temperature
    Protect from light
    Controlled Drug – stored in ICU CD cupboard
  • IM:
    May be given IM – no more than 5ml of solution at any one site
  • PO:
    Tablets:
    Phenobarbitone 15mg and 30mg tablets (white)
    Oral Liquid: Phenobarbitone oral liquid 10mg/ml

DOSAGE:

  • IV:
    Loading dose of 20mg/kg.
  • PO, IM, IV:
    Usual maintenance 300mg/day

DOSAGE IN RENAL FAILURE AND RENAL REPLACEMENT THERAPY:

  • Dose in renal impairment [GFR (ml/min)]
    <10: reduce dose by 25-50%; avoid very large doses
    10-20: reduce dose by 25-50%; avoid very large doses
    >20-50: dose as in normal renal function but avoid very large doses
  • Dose in renal replacement therapy
    CAPD: reduce dose by 25-50%; avoid very large doses
    HD: dose as in normal renal function but avoid very large doses
    CVVHDF: dose as in normal renal function

DOSAGE IN PAEDIATRICS:

  • IV:
    20mg/kg over 20 minutes.
    If necessary may be given as IV push over 5-10 mins

CLINICAL PHARMACOLOGY:

  • The barbiturates are nonselective central nervous system (CNS) depressants which are primarily used as sedative hypnotics and are also anticonvulsants in subhypnotic doses.

CONTRAINDICATIONS:

  1. known barbiturate sensitivity
  2. porphyria
  3. marked impairment of liver function

WARNINGS

  • IV Administration:
    Rapid administration may cause respiratory depression, apnea, laryngospasm, or vasodilation with fall in blood pressure.

PRECAUTIONS

  • General:
    Parenteral solutions of barbiturates are highly alkaline. Therefore, extreme care should be taken to avoid perivascular extravasation or intra-arterial injection. Extravascular injection may cause local tissue damage with subsequent necrosis; consequences of intra-arterial injection may vary from transient pain to gangrene of the limb. Any complaint of pain in the limb warrants stopping the injection.
  • Laboratory Tests:
    No tests in addition to routine ICU tests are indicated
  • Drug/Laboratory Test Interactions:
    None noted

IMPORTANT DRUG INTERACTIONS FOR THE ICU

  • Warfarin:
    Phenobarbital lowers the plasma levels of warfarin and causes a decrease in anticoagulant activity as measured by the prothrombin time. Corticosteroids Barbiturates appear to enhance the metabolism of exogenous corticosteroids, probably through the induction of hepatic microsomal enzymes. Patients stabilized on corticosteroid therapy may require dosage adjustments if barbiturates are added to or withdrawn from their dosage regimen.
  • Phenytoin, Sodium Valproate:
    The effect of barbiturates on the metabolism of phenytoin appears to be variable. Some investigators report an accelerating effect, while others report no effect. Because the effect of barbiturates on the metabolism of phenytoin is not predictable, phenytoin and barbiturate blood levels should be monitored more frequently if these drugs are given concurrently. Sodium valproate appear to decrease barbiturate metabolism; therefore, barbiturate blood levels should be monitored and appropriate dosage adjustments made as indicated.
  • Central Nervous System Depressants:
    The concomitant use of other central nervous system depressants, including other sedatives or hypnotics, antihistamines, tranquilizers, or alcohol, may produce additive depressant effects.

ADVERSE REACTIONS

  • Body as a Whole:
    hypersensitivity reactions (angioedema, skin rashes, exfoliative dermatitis), fever
  • Nervous System:
    Agitation, headache, confusion, hyperkinesia, ataxia, CNS depression, nightmares, nervousness, psychiatric disturbance, hallucinations, insomnia, anxiety, dizziness, thinking abnormality.
  • Respiratory System:
    Hypoventilation, apnea.
  • Cardiovascular System:
    Bradycardia, hypotension, syncope.
  • Digestive System:
    Nausea, vomiting, constipation, liver damage.
  • Haematological System:
    Megaloblastic anaemia following chronic phenobarbital use.

Critical Care Drug Manual

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