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Phenobarbital sodium parenteral


Parenteral formulations of phenobarbital sodium.

Drugs List

  • phenobarbital sodium 200mg/1ml injection
  • phenobarbital sodium 30mg/1ml injection
  • phenobarbital sodium 60mg/1ml injection
  • Therapeutic Indications


    Epilepsy - except absence seizures
    Status epilepticus



    A single dose of 50mg to 200mg given by intramuscular or subcutaneous injection.
    By intravenous injection dilute injection solution with ten times its own volume of water.
    After 6 hours, repeat if necessary.

    The following alternate dosing schedule may be suitable for status epilepticus:
    Dilute the injection solution 1 in 10 with water and administer 10mg/kg at a rate below 100mg per minute. The maximum dose should not exceed 1g.


    A single dose of 3mg/kg to 5mg/kg of body weight given by intramuscular injection.

    The following alternate dosing schedule may be suitable for status epilepticus:
    Children aged 12 to 18 years
    Initial dose: 20mg/kg at a rate below 1 mg/kg per minute.
    Then 300 mg twice a day.

    Children from Birth to 11 years
    Initial dose: 20 mg/kg at a rate below 1mg/kg per minute.
    Then 2.5mg/kg to 5mg/kg once or twice a day.


    Acute porphyria
    Severe hepatic disorder
    Severe renal impairment
    Severe respiratory depression

    Precautions and Warnings

    Children under 18 years
    Hepatic impairment
    History of alcohol abuse
    History of drug misuse
    Renal impairment
    Respiratory impairment

    Advise ability to drive/operate machinery may be affected by side effects
    Increased risk of osteomalacia; consider vitamin D supplement
    Monitor for mental changes, suicidal depression and antisocial behaviour
    Prolonged or excessive use may result in dependence
    Advise patients/carers to seek medical advice if suicidal intent develops
    Hyperactivity may be exacerbated
    Rebound effect may occur after cessation of treatment
    Tolerance may develop with continued use
    May affect results of some laboratory tests
    May affect thyroid function tests
    Do not withdraw this drug suddenly
    Advise patient not to take St John's wort concurrently
    Advise patient to avoid alcohol during treatment
    Advise that effects are potentiated by CNS depressants (including alcohol)
    Female: Effect of hormonal contraceptive may be reduced
    Neonate exposed in utero: Administer vitamin K at birth
    Pregnancy: Administer vitamin K in the last few weeks of pregnancy
    Pregnancy: Advise taking folate supplement as risk of neural tube defects

    Long-term treatment with phenobarbital is associated with decreased bone mineral density, resulting in an increased risk of developing osteopenia, osteoporosis and fractures in at-risk patients (those immobilised for long periods or who have inadequate sun exposure or dietary calcium intake). Consider vitamin D supplementation for all at-risk patients on long-term treatment.

    Pregnancy and Lactation


    Use phenobarbital sodium with caution in pregnancy.

    Phenobarbital can cross the placenta. Studies have shown that phenobarbital can increase the risks of teratogenic effects when used in pregnancy. Briggs (2015) states that taking phenobarbital during pregnancy increases the risk of congenital defects such as a haemorrhage at birth or addiction. It can interfere with the uptake of folic acid, causing folic acid deficiency, therefore it is recommended to take folic acid supplements before conception and throughout pregnancy (Schaefer et al, 2015).
    Phenobarbital is also known to induce enzymes that can lead to a reduction in vitamin K-dependent clotting factor which in turn can increase the risk of neonatal bleeding. Schaefer (2015) states that it is recommended for the mother to take prophylactic treatment with vitamin K1 before delivery and also administer vitamin K1 to the neonate immediately after delivery.

    Briggs (2015) states that there is a greater risk to the mother if phenobarbital is not administered during pregnancy and seizure control is lost. The manufacturer suggests to only use phenobarbital during the first and third trimester if the potential benefits to the mother outweigh any potential risks to the foetus.

    The use of all medication in pregnancy should be avoided whenever possible; particularly in the first trimester. Non-drug treatments should also be considered. When essential, a medication with the best safety record over time should be chosen, employing the lowest effective dose for the shortest possible time. Polypharmacy should be avoided. Teratogens taken in the pre-embryonic period, often quoted as lasting until 14 to 17 days post-conception, are believed to have an all-or-nothing effect. Where drugs have a short half-life, and when the date of conception is certain, this may allow women to be reassured where drug exposure has occurred within this time frame. Further advice may be available from the UK National Teratology Information Service (NTIS) and through ToxBase, available via password on the internet ( ) or if this is unavailable at the backup site ( ).


    Phenobarbital sodium is contraindicated in breastfeeding.

    Phenobarbital is excreted in breast milk. Schaefer (2015) states that a breastfed infant could receive a significant amount of phenobarbital sodium if taken during breastfeeding, which can potentially result in sedating the infant. Hale (2014) and Briggs (2015) also support Schaefer stating that high concentrations of phenobarbital are likely to accumulate in the blood of the infant due to its long half life. It is advisable to monitor the infant if using phenobarbital during breastfeeding, especially if administering high doses due to the increased risk of sedating the infant (Briggs et al, 2015).

    The Drugs and Lactation Database (LactMed) states using phenobarbital during breastfeeding can decrease withdrawal symptoms in the infant if they were exposed to the drug in the uterus. The manufacturer states breastfeeding is not recommended when administering phenobarbital sodium.

    Neonates, infants born prematurely, those with low birth weight, those with an unstable gastrointestinal function or who have serious illnesses may require special consideration. For any infant, if a drug is prescribed to the nursing mother, it should be at the lowest practical dose and for the shortest time. When drug administration is unavoidable and breastfeeding is to continue, minimisation of exposure of the infant to the drug may sometimes be achieved by timing the maternal doses to just after a feeding episode. Infants exposed to drugs via breast milk should be monitored for unusual signs or symptoms. Interactions between the drug received by the infant from the mother's milk and medication prescribed for the infant should also be considered, for example, when the drug given to the infant may prevent metabolism of the drug received via breast milk.
    Specialist advice is available from the UK Drugs in Lactation Advisory Service at

    Side Effects

    Allergic skin reactions
    Aplastic anaemia
    Behavioural disturbances
    Cognitive impairment
    Disturbed vitamin D metabolism
    Dupuytren's contracture
    Erythema multiforme
    Excitement (paradoxical)
    Exfoliative dermatitis
    Fixed drug eruption
    Folate deficiency
    Hyperexcitability (children)
    Impaired memory
    Liver function disturbances
    Macrocytic anaemia
    Maculopapular rash
    Megaloblastic anaemia
    Mental status changes
    Metabolic bone disease
    Morbilliform eruption
    Necrosis (injection site)
    Paradoxical reactions
    Purpura exfoliative dermatitis
    Renal rickets
    Respiratory depression
    Scarlatiniform rash
    Stevens-Johnson syndrome
    Toxic epidermal necrolysis
    Withdrawal symptoms

    Withdrawal Symptoms and Signs

    Abrupt withdrawal should be avoided due to the risk of rebound seizures and withdrawal symptoms. A severe withdrawal syndrome may be precipitated including the following symptoms, rebound insomnia, anxiety, tremor, dizziness, nausea, fits and delirium.


    It is strongly recommended that the UK National Poisons Information Service be consulted on cases of suspected or actual overdose where there is doubt over the degree of risk or about appropriate management.

    The following number will direct the caller to the relevant local centre (0844) 892 0111

    Information may be obtained if you have access to ToxBase the primary clinical toxicology database of the National Poisons Information Service. This is available via password on the internet ( ) or if this is unavailable at the backup site ( ).

    Reference Sources

    Drugs During Pregnancy and Lactation: Treatment Options and Risk Assessment, 3rd edition (2015) ed. Schaefer, C., Peters, P. and Miller, R. Elsevier, London.

    Drugs in Pregnancy and Lactation: A Reference Guide to Fetal and Neonatal Risk, 10th edition (2015) ed. Briggs, G., Freeman, R. Wolters Kluwer Health, Philadelphia.

    Medications and Mothers' Milk, Sixteenth Edition (2014) Hale, T and Rowe, H, Hale Publishing, Plano, Texas.

    Summary of Product Characteristics: Phenobarbital Sodium Injection BP 30 mg/ml. Martindale Pharma. Revised November 2012.

    Summary of Product Characteristics: Phenobarbital Sodium Injection BP 60 mg/ml. Martindale Pharma. Revised November 2012.

    Summary of Product Characteristics: Phenobarbital Sodium Injection BP 200 mg/ml. Martindale Pharma. Revised November 2012.

    US National Library of Medicine. Toxicology Data Network. Drugs and Lactation Database (LactMed).
    Available at:
    <.Phenobarbital> Last revised: 07 September 2013
    Last accessed: 08 March 2017

    NICE Evidence Services Available at: Last accessed: 14 September 2017

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