▶INITIALLY BY SLOW INTRAVENOUS INJECTION
▶Neonate:Loading dose 18 mg/kg, dose to be
administered over 20 – 30 minutes, then (by mouth)
2. 5 – 5 mg/kg twice daily (max. per dose
7. 5 mg/kg twice daily), adjusted according to response,
dose also adjusted according to plasma-phenytoin
concentration.Prevention and treatment of seizures during or following
neurosurgery or severe head injury
▶BY MOUTH
▶Child:Initially 2. 5 mg/kg twice daily, then adjusted
according to response to 4 – 8 mg/kg daily, dose also
adjusted according to plasma-phenytoin
concentration; maximum 300 mg per day
Status epilepticus|Acute symptomatic seizures associated
with head trauma or neurosurgery
▶INITIALLY BY SLOW INTRAVENOUS INJECTION, OR BY
INTRAVENOUS INFUSION
▶Neonate:Loading dose 20 mg/kg, then (by slow
intravenous injection or by intravenous infusion)
2. 5 – 5 mg/kg twice daily.▶Child 1 month–11 years:Loading dose 20 mg/kg, then (by
slow intravenous injection or by intravenous infusion)
2. 5 – 5 mg/kg twice daily
▶Child 12–17 years:Loading dose 20 mg/kg, then (by
intravenous infusion or by slow intravenous injection)
up to 100 mg 3 – 4 times a day
DOSE EQUIVALENCE AND CONVERSION
▶Preparations containing phenytoin sodium arenot
bioequivalent to those containing phenytoin base
(such asEpanutin Infatabs®andEpanutin®
suspension); 100 mg of phenytoin sodium is
approximately equivalent in therapeutic effect to
92 mg phenytoin base. The dose is the same for all
phenytoin products when initiating therapy. However,
if switching between these products the difference in
phenytoin content may be clinically significant. Care is
needed when making changes between formulations
and plasma-phenytoin concentration monitoring is
recommended.lUNLICENSED USE
▶With oral useLicensed for use in children (age range not
specified by manufacturer).
▶With intravenous usePhenytoin doses in BNF publications
may differ from those in product literature.IMPORTANT SAFETY INFORMATION
NHS IMPROVEMENT PATIENT SAFETY ALERT: RISK OF DEATH AND
SEVERE HARM FROM ERROR WITH INJECTABLE PHENYTOIN
(NOVEMBER 2016)
Use of injectable phenytoin is error-prone throughout
the prescribing, preparation, administration and
monitoring processes; all relevant staff should be made
aware of appropriate guidance on the safe use of
injectable phenytoin to reduce the risk of error.lCONTRA-INDICATIONS
GENERAL CONTRA-INDICATIONSAcute porphyrias p. 603
SPECIFIC CONTRA-INDICATIONS
▶With intravenous useSecond- and third-degree heart block.
sino-atrial block.sinus bradycardia.Stokes-Adams
syndrome
lCAUTIONS
GENERAL CAUTIONSEnteral feeding (interrupt feeding for
2 hours before and after dose; more frequent monitoring
may be necessary)SPECIFIC CAUTIONS
▶With intravenous useHeart failure.hypotension.injection
solutions alkaline (irritant to tissues).respiratory
depression.resuscitation facilities must be available
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.
Intramuscular phenytoin should not be used (absorption
is slow and erratic).
lINTERACTIONS→Appendix 1 : antiepileptics
lSIDE-EFFECTS
GENERAL SIDE-EFFECTSAgranulocytosis.bone disorders.
bone fracture.bone marrow disorders.cerebrovascular
insufficiency.coarsening of the facial features.confusion.
constipation.dizziness.drowsiness.Dupuytren’s
contracture.dysarthria.eosinophilia.fever.gingival
hyperplasia (maintain good oral hygiene).
granulocytopenia.hair changes.headache.hepatic
disorders.hypersensitivity.insomnia.joint disorders.
leucopenia.lip swelling.lymphatic abnormalities.
macrocytosis.megaloblastic anaemia.movement
disorders.muscle twitching.nausea.neoplasms.
nephritis tubulointerstitial.nervousness.nystagmus.
paraesthesia.Peyronie’s disease.polyarteritis nodosa.
pseudolymphoma.sensory peripheral polyneuropathy.
severe cutaneous adverse reactions (SCARs).skin
reactions.systemic lupus erythematosus (SLE).taste
altered.thrombocytopenia.tremor.vertigo.vomiting
SPECIFIC SIDE-EFFECTS
▶With oral useElectrolyte imbalance.pneumonitis.vitamin
Ddeficiency
▶With parenteral useArrhythmias.atrial conduction
depression (more common if injection too rapid).cardiac
arrest.hypotension.purple glove syndrome.respiratory
arrest (more common if injection too rapid).respiratory
disorders.tonic seizure (more common if injection too
rapid).ventricular conduction depression (more common
if injection too rapid).ventricularfibrillation (more
common if injection too rapid)
SIDE-EFFECTS, FURTHER INFORMATION
RashDiscontinue; if mild re-introduce cautiously but
discontinue immediately if recurrence.
Bradycardia and hypotensionWith intravenous use;
reduce rate of administration if bradycardia or
hypotension occurs.
OverdoseSymptoms of phenytoin toxicity include
nystagmus, diplopia, slurred speech, ataxia, confusion,
and hyperglycaemia.
lALLERGY AND CROSS-SENSITIVITYCross-sensitivity
reported with carbamazepine. Antiepileptic
hypersensitivity syndrome associated with phenytoin. See
under Epilepsy p. 191 for more information.
lPREGNANCY
MonitoringChanges in plasma-protein binding make
interpretation of plasma-phenytoin concentrations
difficult—monitor unbound fraction.
Doses should be adjusted on the basis of plasma-drug
concentration monitoring.
lBREAST FEEDINGSmall amounts present in milk, but not
known to be harmful.
lHEPATIC IMPAIRMENT
Dose adjustmentsReduce dose to avoid toxicity.
lPRE-TREATMENT SCREENINGHLAB* 1502 allele in
individuals of Han Chinese or Thai origin—avoid unless
essential (increased risk of Stevens- Johnson syndrome).
lMONITORING REQUIREMENTS
▶Therapeutic plasma-phenytoin concentrations reduced in
first 3 months of life because of reduced protein binding.206 Epilepsy and other seizure disorders BNFC 2018 – 2019
Nervous system4