Indicated for the treatment of generalized tonic-clonic status epilepticus, and prevention and treatment of seizures occurring during neurosurgery.
An anti-seizure medication.
Phenytoin acts as an anticonvulsant by increasing efflux or decreasing influx of sodium ions across cell membranes in the motor cortex during generation of nerve impulses; thus stabilising neuronal membranes and decreasing seizure activity. It acts as an antiarrhythmic by extending the effective refractory period and suppressing ventricular pacemaker automaticity, shortening action potential in the heart.
Tonic-clonic seizures | Focal seizures | Prevention and treatment of seizures during or following neurosurgery or severe head injury BY MOUTH Child 1 month-11 years: Initially 1.5-2.5 mg/kg twice daily, then adjusted according to response to 2.5-5 mg/kg twice daily (max. per dose 7.5 mg/kg twice daily), dose also adjusted according to plasmaphenytoin concentration; maximum 300 mg per day Child 12-17 years: Initially 75-150 mg twice daily, then adjusted according to response to 150-200 mg twice daily (max. per dose 300 mg twice daily), dose also adjusted according to plasma-phenytoin concentration Adult: Initially 3-4 mg/kg daily, alternatively 150-300 mg once daily, alternatively 150-300 mg daily in 2 divided doses, alternatively maintenance 200-500 mg daily, to be taken preferably with or after food, dose to be increased gradually as necessary (with plasma-phenytoin concentration monitoring), exceptionally, higher doses may be used Status epilepticus | Acute symptomatic seizures associated with head trauma or neurosurgery INITIALLY BY SLOW INTRAVENOUS INJECTION, OR BY INTRAVENOUS INFUSION 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, to be given with blood pressure and ECG monitoring 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, to be given with blood pressure and ECG monitoring Adult: Loading dose 20 mg/kg (max. per dose 2 g), to be given at a rate not exceeding 1 mg/kg/minute (max. 50 mg per minute), to be given with blood pressure and ECG monitoring, then (by intravenous infusion or by slow intravenous injection or by mouth) maintenance 100 mg every 6-8 hours adjusted according to plasmaconcentration monitoring, to be given with blood pressure and ECG monitoring DOSE EQUIVALENCE AND CONVERSION Preparations containing phenytoin sodium are not bioequivalent to those containing phenytoin base (such as Epanutin Infatabs - and Epanutin - suspension); 100mg 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.
Effects with other sedative drugs or ethanol may be potentiated. Enhances toxic effects of paracetamol, lithium. Increased risk of osteomalacia with acetazolamide. Decreased serum levels/effects with acyclovir, antineoplastics, benzodiazeines, ciprofloxacin, CYP2C9 inducers (e.g. carbamazepine), CYP2C19 inducers (e.g. rifampin), folic acid, vigabatrin. Increased serum concentrations with allopurinol, capecitabine, cimetidine, CYP2C9 inhibitors (e.g. fluconazole), CYP2C19 inhibitors (e.g. delavirdine), disulfiram, methylphenidate, metronidazole, omeprazole, SSRI, trazodone, trimethoprim. Increases metabolism of antiarrhythmics, anticonvulsants, antipsychotics, beta-blockers, calcium channel blockers, chloramphenicol, corticosteroids, doxycycline, oestrogens, HMG-CoA reductase inhibitors, methadone, theophylline, TCAs. Decreases levels/effects of clozapine, ciclosporin, tacrolimus, CYP2B6 substrates (e.g. bupropion, selegiline), CYP2C8 substrates (e.g. amiodarone), CYP2C9 substrates (e.g. celecoxib), CYP2C19 substrates (e.g. citalopram), CYP3A4 substrates (e.g. benzodiazepines), digoxin, itraconazole, levodopa, neuromuscular-blocking agents, thyroid hormones, topiramate. Increases levels/effect of dopamine, ticlopidine. Valproic acid may displace phenytoin from binding sites; and affect phenytoin serum concentrations. Transiently increases the hypothrombinaemia response to warfarin initially, followed by an inhibition of the response.
CONTRA-INDICATIONS GENERAL CONTRA-INDICATIONS Acute porphyrias p. 930 SPECIFIC CONTRA-INDICATIONS With intravenous use Second- and third-degree heart block . sino-atrial block . sinus bradycardia . Stokes-Adams syndrome PRECAUTIONS GENERAL CAUTIONS Enteral feeding (interrupt feeding for 2 hours before and after dose; more frequent monitoring may be necessary) SPECIFIC CAUTIONS With intravenous use Heart failure . hypotension . injection solutions alkaline (irritant to tissues) . respiratory depression . resuscitation facilities must be available CAUTIONS, FURTHER INFORMATION Consider 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).
Common or very common Acne . anorexia . coarsening of facial appearance . constipation . dizziness . drowsiness . gingival hypertrophy and tenderness (maintain good oral hygiene) . headache . hirsutism . insomnia . nausea . paraesthesia . rash . transient nervousness . tremor . vomiting Rare Leucopenia . aplastic anaemia . blood disorders . dyskinesia . hepatotoxicity . lupus erythematosus . lymphadenopathy . megaloblastic anaemia . osteomalacia . peripheral neuropathy . polyarteritis nodosa . Stevens- Johnson syndrome . thrombocytopenia . toxic epidermal necrolysis Frequency not known Hypersensitivity syndrome . interstitial nephritis . pneumonitis . polyarthropathy . suicidal ideation.
PREGNANCY Changes 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. BREAST FEEDING Small amounts present in milk, but not known to be harmful.
Keep below 30°C temperature, away from light & moisture. Keep out of the reach of children.
.png&w=384&q=75)