OverdoseFor details on the management of poisoning, see
Active elimination techniques, under Emergency
treatment of poisoning p. 832.lALLERGY AND CROSS-SENSITIVITYAntiepileptic
hypersensitivity syndrome associated with phenobarbital.
See under Epilepsy p. 191 for more information.
lPREGNANCY
MonitoringThe dose should be monitored carefully during
pregnancy and after birth, and adjustments made on a
clinical basis.
lBREAST FEEDINGAvoid if possible; drowsiness may occur.
lHEPATIC IMPAIRMENTMay precipitate coma. Avoid in
severe impairment.
lRENAL IMPAIRMENTUse with caution.
lMONITORING REQUIREMENTS
▶Plasma-phenobarbital concentration for optimum
response is 15 – 40 mg/litre ( 60 – 180 micromol/litre);
however, monitoring the plasma-drug concentration is
less useful than with other drugs because tolerance occurs.
lTREATMENT CESSATIONAvoid abrupt withdrawal
(dependence with prolonged use).
lDIRECTIONS FOR ADMINISTRATION
▶With oral useFor administration bymouth, tablets may be
crushed.
▶With intravenous useForintravenous injection, dilute to a
concentration of 20 mg/mL with Water for Injections; give
over 20 minutes (no faster than 1 mg/kg/minute).
lPRESCRIBING AND DISPENSING INFORMATIONSome
hospitals supplyalcohol-freeformulations of varying
phenobarbital strengths. The RCPCH and NPPG
recommend that, when a liquid special of phenobarbital is
required, the following strength is used: 50 mg/ 5 mL.
Switching between formulationsDifferent formulations of oral
preparations may vary in bioavailability. Patients should
be maintained on a specific manufacturer’s product.
lPATIENT AND CARER ADVICE
Medicines for Children leaflet: Phenobarbital for preventing
seizureswww.medicinesforchildren.org.uk/phenobarbital-for-
preventing-seizures
lMEDICINAL FORMS
There can be variation in the licensing of different medicines
containing the same drug. Forms available from special-order
manufacturers include: tablet, capsule, oral suspension, oral
solution
Tablet
CAUTIONARY AND ADVISORY LABELS2, 8
▶Phenobarbital (Non-proprietary)
Phenobarbital 15 mgPhenobarbital 15 mg tablets| 28 tabletP
£ 24. 95 DT = £ 16. 72 c
Phenobarbital 30 mgPhenobarbital 30 mg tablets| 28 tabletP
£ 5. 99 DT = £ 0. 44 c
Phenobarbital 60 mgPhenobarbital 60 mg tablets| 28 tabletP
£ 7. 99 DT = £ 6. 03 c
Solution for injection
EXCIPIENTS:May contain Propylene glycol
▶Phenobarbital (Non-proprietary)
Phenobarbital sodium 30 mg per 1 mlPhenobarbital 30 mg/ 1 ml
solution for injection ampoules| 10 ampouleP£ 89. 47 DT =
£ 89. 47 c
Phenobarbital sodium 60 mg per 1 mlPhenobarbital 60 mg/ 1 ml
solution for injection ampoules| 10 ampouleP£ 94. 40 c
Phenobarbital sodium 200 mg per 1 mlPhenobarbital 200 mg/ 1 ml
solution for injection ampoules| 10 ampouleP£ 76. 96 DT =
£ 76. 96 c
Oral solution
CAUTIONARY AND ADVISORY LABELS2, 8
EXCIPIENTS:May contain Alcohol
▶Phenobarbital (Non-proprietary)
Phenobarbital 3 mg per 1 mlPhenobarbital 15 mg/ 5 ml elixir|
500 mlP£ 83. 00 – £ 83. 16 DT = £ 83. 08 c
Primidone
lINDICATIONS AND DOSE
All forms of epilepsy except typical absence seizures
▶BY MOUTH
▶Child 1 month–1 year:Initially 125 mg daily, dose to be
taken at bedtime, then increased in steps of 125 mg
every 3 days, adjusted according to response;
maintenance 125 – 250 mg twice daily
▶Child 2–4 years:Initially 125 mg once daily, dose to be
taken at bedtime, then increased in steps of 125 mg
every 3 days, adjusted according to response;
maintenance 250 – 375 mg twice daily
▶Child 5–8 years:Initially 125 mg once daily, dose to be
taken at bedtime, then increased in steps of 125 mg
every 3 days, adjusted according to response;
maintenance 375 – 500 mg twice daily
▶Child 9–17 years:Initially 125 mg once daily, dose to be
taken at bedtime, then increased in steps of 125 mg
every 3 days, increased to 250 mg twice daily, then
increased in steps of 250 mg every 3 days (max. per
dose 750 mg twice daily), adjusted according to
responselCAUTIONSAvoid in Acute porphyrias p. 603 .children.
debilitated.history of alcohol abuse.history of drug abuse
.respiratory depression (avoid if severe)
CAUTIONS, FURTHER INFORMATIONConsider vitamin D
supplementation in patients who are immobilised for long
periods or who have inadequate sun exposure or dietary
intake of calcium.
lINTERACTIONS→Appendix 1 : antiepileptics
lSIDE-EFFECTS
▶Common or very commonApathy.ataxia.drowsiness.
nausea.nystagmus.visual impairment
▶UncommonDizziness.headache.hypersensitivity.skin
reactions.vomiting
▶Rare or very rareArthralgia.blood disorder.bone
disorders.Dupuytren’s contracture.megaloblastic
anaemia (may be treated with folic acid).personality
change.psychotic disorder.severe cutaneous adverse
reactions (SCARs).systemic lupus erythematosus (SLE)
▶Frequency not knownBone fracture
lALLERGY AND CROSS-SENSITIVITYAntiepileptic
hypersensitivity syndrome associated with primidone. See
under Epilepsy p. 191 for more information.
lPREGNANCY
MonitoringThe dose should be monitored carefully during
pregnancy and after birth, and adjustments made on a
clinical basis.
lHEPATIC IMPAIRMENTMay precipitate coma.
Dose adjustmentsReduce dose.
lRENAL IMPAIRMENTUse with caution.
lMONITORING REQUIREMENTS
▶Monitor plasma concentrations of derived phenobarbital;
plasma concentration for optimum response is
15 – 40 mg/litre ( 60 – 180 micromol/litre).
lTREATMENT CESSATIONAvoid abrupt withdrawal
(dependence with prolonged use).
lPRESCRIBING AND DISPENSING INFORMATION
Switching between formulationsDifferent formulations of oral
preparations may vary in bioavailability. Patients being
treated for epilepsy should be maintained on a specific
manufacturer’s product.BNFC 2018 – 2019 Epilepsy and other seizure disorders 217
Nervous system4