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Disclaimer to the On-line Edition
This Manual has been designed for use in the NICU at London Health Sciences Centre (LHSC), London, Ontario, Canada, and represents clinical practice at this institution. The information contained within the Manual may not be applicable to other centres. If users of this Manual are not familiar with a drug, it is recommended that the official monograph be consulted before it is prescribed and administered. Any user of this information is advised that the contributors, Editor and LHSC are not responsible for any errors or omissions, and / or any consequences arising from the use of the information in this Manual.

PHENOBARBITAL

Indication

  • management of neonatal seizures, neonatal withdrawal syndrome, neonatal hyperbilirubinemia and to provide sedation

Pharmacology

  • phenobarbital limits the spread of seizure activity and may increase seizure threshold; its exact mechanism of action is unknown
  • phenobarbital induces hepatic microsomes and increases bilirubin metabolism; it takes 3 to 7 days to become effective; phototherapy remains the most common method to treat neonatal hyperbilirubinemia, however; there is no advantage in combining phenobarbital treatment with phototherapy
  • 50 to 70% of a dose is metabolized by the liver; 20 to 30% is excreted unchanged in the urine
  • the half life has been reported to range from 40 to more than 400 hours, depending on the maturation of the neonate's liver and kidney function, and any endogenous or exogenous (eg. drugs) substances which could interfere with its metabolism
  • for anticonvulsant activity, recommended serum phenobarbital level is 65-170 micromol/L

Side Effects

  • may cause respiratory depression when given IV; be prepared to ventilate the infant
  • hypotension and apnea, especially with cumulative loading doses greater than 20 mg/kg
  • skin eruptions, skin rash
  • drowsiness, sedation, occasional paradoxical excitation

Precautions

  • may increase the metabolism of other drugs (eg. theophylline)
  • serum concentrations will likely be altered (increased or decreased) when the patient is also being treated with phenytoin

Dose

  • doses should ALWAYS be checked by 2 RNs

    FOR TREATMENT OF SEIZURES

    • first, ensure that the infant is not hypoglycemic or hypocalcemic
    1. LOADING DOSE
      • 20 mg/kg IV push over approximately 10 minutes; additional doses of 10 mg/kg may be given every 5 minutes until seizures have ceased or a total dose of 40 mg/kg has been reached
      • phenytoin is indicated only if phenobarbital fails to control seizures
    2. MAINTENANCE DOSE
      • only if the seizures continue is a maintenance dose utilized
      • start maintenance dose 12 to 24 h after loading dose
      • 3 to 5 mg/kg/day IV (push), PO, PR
      • may be given once daily because of its long half-life in neonates
      • in patients who remain symptomatic or are unusually depressed, phenobarbital levels are indicated

    FOR TREATMENT OF NEONATAL WITHDRAWAL

    • loading dose of 20 mg/kg, followed 12 to 24h later by maintenance dose of approximately 5mg/kg/d
    • the actual maintenance dose should be determined by the clinical response
    • vomiting and diarrhea are not helped, and poor sucking and feeding may be made worse; therefore, phenobarbital is not the appropriate drug if the prominent clinical signs/symptoms of neonatal withdrawal are gastro-intestinal

    TREATMENT OF HYPERBILIRUBINEMIA

    • dose not clearly established
    • 5 mg/kg/day is the dose most commonly used
    • the effect on bilirubin metabolism is not immediate; this may take several days to develop
    • not the present recommended management of hyperbilirubinemia in our nursery

Supplied

  • 30 mg/mL ampoule for IV use
  • 5 mg/mL oral solution

References

  1. Cloherty JP and Stark AR (eds): Manual of Neonatal Intensive Care, Little, Brown and Company, 1991.
  2. Roberts, RJ: Drug Therapy in Infants, W.B. Saunders, Toronto, 1984.
  3. Gomella TL (Ed): Neonatology - Management, Procedures, On-Call Problems, Diseases, Drugs, 1992, Appleton and Lange, Norwalk, Connecticut.
  4. Volpe JJ: Neurology of the Newborn, Sanders, Toronto, 1987.
  5. Taketomo CK, Hodding JH and Kraus DM: Pediatric Dosage Handbook, Lexi-Comp Inc., Cleveland, 1992.
  6. Young TE and Mangum OB: Neofax - A Manual of Drugs Used in Neonatal Care, Columbus, Ohio: Ross Laboratories, 1992.
  7. Zenk KE, Sills JH, Koeppel RM : Neonatal Medication & Nutrition - A Comprehensive Guide, NICU Link, Santa Rosa, CA,1999

Updated: 17 March 2004


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