Phenytoin: Difference between revisions
 
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*Dosage Forms: capsules 50, 100, 200, 300  125/5 mL IM/IV
*Dosage Forms: capsules 50, 100, 200, 300  125/5 mL IM/IV
*Common Trade Names: Dilantin, Phenytek
*Common Trade Names: Dilantin, Phenytek
*Often combined with propylene glycol to increase water solubility
**If infused too quickly, can lead to dysrhythmias, hypotension, bradycardia, seizures, and lactic acidosis


==Adult Dosing==
==Adult Dosing==
*Status Epilepticus
===[[Status epilepticus]]===
**Loading dose: 15-20 mg/kg IV; if ineffective, can give 10 mg/kg IV 20 min after first dose
*Loading dose: 15-20mg/kg IV; if ineffective, can give 10mg/kg IV 20 min after first dose
**Maintenance dose:  100 mg PO/IV q 6-8hrs
*Maintenance dose:  100mg PO/IV q 6-8hrs
**Start 12 hours after loading dose
*Start 12 hours after loading dose


*Seizure disorder
===[[Seizure]] disorder===
**300-400 mg/day divided into 2-3 doses/day (Max 400 mg/dose)
*300-400mg/day divided into 2-3 doses/day (Max 400mg/dose)
**May give 4-7 mg/kg/day divided into 2-3 doses/day
*May give 4-7mg/kg/day divided into 2-3 doses/day
**Consider loading dose: 15-20 mg/kg divided into 2-3 doses given 2-4 hrs apart
*Consider loading dose: 15-20mg/kg divided into 2-3 doses given 2-4 hrs apart
**Adjust dose on response and serum levels
*Adjust dose on response and serum levels
**Available in extended or immediate release
*Available in extended or immediate release


*Seizure prophylaxis (neurosurgery)
===[[Seizure]] prophylaxis (neurosurgery)===
**Loading dose:  10-20 mg/kg IV in 3 doses 2-4 hrs apart (max 400 mg/dose)
*Loading dose:  10-20mg/kg IV in 3 doses 2-4 hrs apart (max 400mg/dose)
**4-6 mg/kg/day IV divided into 2-3 doses/day
*4-6mg/kg/day IV divided into 2-3 doses/day
**Can give IM route, though IV prefered
*Can give IM route, though IV prefered
***100-200 mg IM q 4 hrs x 1 week
**100-200mg IM q 4 hrs x 1 week
***150% PO dose by IM route if previously on medication
**150% PO dose by IM route if previously on medication


==Pediatric Dosing==
==Pediatric Dosing==
*Status Epilepticus
===[[Seizure (peds)|Status epilepticus]]===
**Loading dose:  15-20 mg/kg IV; if ineffective, can give 10 mg/kg IV 20 min after first dose
*Loading dose:  15-20mg/kg IV; if ineffective, can give 10mg/kg IV 20 min after first dose
**Max 1500 mg/day
*Max 1500mg/day
**Start maintenance 12 hrs after loading dose
*Start maintenance 12 hrs after loading dose


*Seizure disorder: All doses are divided into 2-3 doses/day; always start at 5 mg/kg/day and titrate based on effect and serum levels
===[[Seizure (peds)|Seizure]] disorder===
**<6 mo:  5-8 mg/kg/day PO/IV
''All doses are divided into 2-3 doses/day; always start at 5mg/kg/day and titrate based on effect and serum levels''
**6mo-4 yrs:  8-10 mg/kg/day PO/IV
*<6 mo:  5-8mg/kg/day PO/IV
**4-7yrs:  7.5-9 mg/kg/day PO/IV
*6mo-4 yrs:  8-10mg/kg/day PO/IV
**7-10 yrs:  7-8 mg/kg/day PO/IV
*4-7yrs:  7.5-9mg/kg/day PO/IV
**10-16 yrs:  6-7 mg/kg/day PO/IV
*7-10 yrs:  7-8mg/kg/day PO/IV
**>16 yrs use adult dosing
*10-16 yrs:  6-7mg/kg/day PO/IV
**For immediate release.  Extended release available for ages >7 at same dosages.
*>16 yrs use adult dosing
*For immediate release.  Extended release available for ages >7 at same dosages.


==Special Populations==
==Special Populations==
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**Hepatic impairment
**Hepatic impairment
**Porphyria
**Porphyria
**DM
**[[Diabetes mellitus]]
**Thyroid disease
**Thyroid disease
**Depression
**Depression
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==Adverse Reactions==
==Adverse Reactions==
''See [[phenytoin toxicity]] for overdose''
''See [[phenytoin toxicity]] for overdose''
{{Phenytoin toxicity level chart}}
===Serious===
===Serious===
*[[V-Fib]] (IV)
*[[V-Fib]] (IV)
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*[[Stevens-Johnson syndrome]]
*[[Stevens-Johnson syndrome]]
*[[Toxic epidermal necrolysis]]
*[[Toxic epidermal necrolysis]]
*Drug rash (w/ eosinophilia)
*Drug rash (with eosinophilia)
*Tissue necrosis (IV)
*Tissue necrosis (IV)
*Purple glove syndrome (IV)
*[[Purple glove syndrome]] (IV)
*[[Anaphylaxis]]
*[[Anaphylaxis]]
*[[Lymphoma]]
*[[Lymphoma]]
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*Somnolence
*Somnolence
*[[Constipation]]
*[[Constipation]]
*[[HA]]
*[[headache]]
*[[Insomnia]]
*[[Insomnia]]
*Gingival hyperplasia
*[[Gingival hyperplasia]]
*Tremor
*Tremor
*Lymphadenopathy
*Lymphadenopathy
*Coarse facies
*Coarse facies
*Hyperglycemia
*[[Hyperglycemia]]
*Osteomalacia
*Osteomalacia
*Phlebitis (IV)
*Phlebitis (IV)
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*[[Seizure levels and reloading]]
*[[Seizure levels and reloading]]
*[[Phenytoin toxicity]]
*[[Phenytoin toxicity]]
*[[Purple glove syndrome]]


==Sources==
==References==
Epocrates
*Epocrates
Medscape
*Medscape


<references/>
<references/>
[[Category:Drugs]]
[[Category:Pharmacology]]
[[Category:Neurology]]

Latest revision as of 03:54, 8 March 2021

General

  • Type: Anticonvulsants
  • Dosage Forms: capsules 50, 100, 200, 300 125/5 mL IM/IV
  • Common Trade Names: Dilantin, Phenytek
  • Often combined with propylene glycol to increase water solubility
    • If infused too quickly, can lead to dysrhythmias, hypotension, bradycardia, seizures, and lactic acidosis

Adult Dosing

Status epilepticus

  • Loading dose: 15-20mg/kg IV; if ineffective, can give 10mg/kg IV 20 min after first dose
  • Maintenance dose: 100mg PO/IV q 6-8hrs
  • Start 12 hours after loading dose

Seizure disorder

  • 300-400mg/day divided into 2-3 doses/day (Max 400mg/dose)
  • May give 4-7mg/kg/day divided into 2-3 doses/day
  • Consider loading dose: 15-20mg/kg divided into 2-3 doses given 2-4 hrs apart
  • Adjust dose on response and serum levels
  • Available in extended or immediate release

Seizure prophylaxis (neurosurgery)

  • Loading dose: 10-20mg/kg IV in 3 doses 2-4 hrs apart (max 400mg/dose)
  • 4-6mg/kg/day IV divided into 2-3 doses/day
  • Can give IM route, though IV prefered
    • 100-200mg IM q 4 hrs x 1 week
    • 150% PO dose by IM route if previously on medication

Pediatric Dosing

Status epilepticus

  • Loading dose: 15-20mg/kg IV; if ineffective, can give 10mg/kg IV 20 min after first dose
  • Max 1500mg/day
  • Start maintenance 12 hrs after loading dose

Seizure disorder

All doses are divided into 2-3 doses/day; always start at 5mg/kg/day and titrate based on effect and serum levels

  • <6 mo: 5-8mg/kg/day PO/IV
  • 6mo-4 yrs: 8-10mg/kg/day PO/IV
  • 4-7yrs: 7.5-9mg/kg/day PO/IV
  • 7-10 yrs: 7-8mg/kg/day PO/IV
  • 10-16 yrs: 6-7mg/kg/day PO/IV
  • >16 yrs use adult dosing
  • For immediate release. Extended release available for ages >7 at same dosages.

Special Populations

  • Pregnancy Rating: D
  • Lactation: Likely safe; limited information. Use caution.
  • Renal Dosing
    • Adult: No oral loading regimen
    • Pediatric: No adjustment
  • Hepatic Dosing
    • Adult: No oral loading regimen
    • Pediatric: Decrease dose, amount not defined

Contraindications

  • Allergy to class/drug
  • Sinus brady/SA block/2nd-3rd AV block
  • Adams-Stokes syndrome
  • Avoid abrupt withdrawl
  • Caution:
    • CV disease
    • Hypotension
    • Alcohol use
    • HLA-B 1502 positive
    • Renal impairment
    • Hepatic impairment
    • Porphyria
    • Diabetes mellitus
    • Thyroid disease
    • Depression
    • Elderly

Adverse Reactions

See phenytoin toxicity for overdose

Toxicity symptoms by phenytoin level^

Level Sypmtoms
>10 Usually no symptoms
10-20 Occasional mild nystagmus
20-30 Nystagmus
30-40 Ataxia, slurred speech, Nausea/vomiting
40-50 Lethargy, confusion
>50 Coma, seizure (rare)

^Provides a rough guide only; neither sensitive nor specific

Serious

Common

Pharmacology

  • Half-life: 7-42 hrs
  • Metabolism: liver; CYP450: 2C9 and 2C19
  • Excretion: bile and urine
  • Mechanism of Action: effects neuronal voltage-dependent NA and CA channels

See Also

References

  • Epocrates
  • Medscape


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