Intravenous phenytoin for status epilepticus in adults
Local Guidance
Note: the following guidance reflects BNF dosing and administration information. Product
information may vary. It is recommended to follow the guideline below for all phenytoin
brands.
Indication: Status epilepticus
Products: Vials contain 250mg phenytoin sodium in 5ml
Contra-indications: hypersensitivity to phenytoin, sinus bradycardia, sino-atrial block, second or third
degree AV block, Stokes-Adams syndrome
PHENYTOIN LOADING DOSE
(for patients not already taking phenytoin)
Dose: 20mg/kg given via intravenous infusion (for patients not already taking phenytoin).
For patients already taking phenytoin, seek advice for loading dose calculations
Table 1: Loading dose of phenytoin sodium
Weight (kg) Loading dose Volume (mL) of phenytoin
(mg) sodium 250mg in 5mL
35-37 700 14
38-42 800 16
43-47 900 18
48-52 1000 20
53-57 1100 22
58-62 1200 24
63-67 1300 26
68-72 1400 28
73-77 1500 30
78-82 1600 32
83-87 1700 34
88-92 1800 36
93-97 1900 38
>98 2000 40
For obese patients (BMI > 30 kg/m2) use adjusted body weight to calculate the loading dose:
Adjusted body weight = IBW+ [1.33 x (actual body weight - IBW)]
Ideal body weight (IBW) for males (kg) = 50 + (2.3 x [height in inches - 60])
Ideal body weight (IBW) for females (kg) = 45.5 + (2.3 x [height in inches - 60])
Note this is specific to IV phenytoin only
How to prepare:
Before and after the infusion of phenytoin the needle or the catheter must be flushed by an injection of
sodium chloride 0.9%.
Dilute in 250ml sodium chloride 0.9% only
After dilution phenytoin must be infused immediately and completed within an hour.
PHENYTOIN LOADING DOSE (continued)
How to administer:
The maximum rate of administration is 50mg per minute:
For doses under 1g: Infuse over 20 minutes via large vein
For doses 1 - 2g: Infuse over 40 minutes via large vein
Use a 0.22 micron filter with the infusion pump during the administration of intravenous phenytoin. If the
ward does not stock 0.22 micron filters, please contact your ward pharmacist or the out-of-hours
pharmacist.
The product should be inspected visually for particulate matter and discolouration prior to administration.
Monitoring:
Monitor BP, ECG, O2 saturation and respiratory rate.
Signs of phenytoin toxicity:
The initial symptoms are symptoms: nystagmus, ataxia and dysarthria. Additional symptoms may
include: lethargy, slurred speech, nausea, vomiting, diplopia, dizziness and tremor. The patient may
become comatose and hypotensive.
PHENYTOIN MAINTENANCE DOSE
Dose:
Initially 100mg every 6-8 hours given IV (usually start with 100mg three times daily).
Dose may be lower in patients with low albumin levels or patients who are receiving other medicines
which interact with phenytoin. Contact your pharmacist for advice about interactions between
medications.
How to prepare and administer: Best practice is to administer as an IV bolus over 3-5 minutes but
can be administered as an infusion.
Supporting information
Therapeutic drug monitoring:
Target phenytoin level is 10-20mg/L
When do I take the level?
After loading dose: Phenytoin levels should be taken between 6-24 hours after loading dose has been
given. Level will be a guide to assess whether the therapeutic range has been achieved or whether the
level exceed the target range.
After maintenance dose: Phenytoin levels should be taken 2-3 weeks after treatment is initiated or
dose has been changed. A trough level is required before the morning dose of phenytoin.
Levels may need to be taken more frequently in malnourished patients, patients with liver impairment or
patient taking medicines which interact with phenytoin.
The pharmacokinetics of phenytoin means that a small dose increase can produce a large increase in
phenytoin levels.
If a dose increase is required then doses should be changed in small increments only to avoid toxicity.
Contact pharmacist or neurologist for advice regarding adjusting phenytoin doses.
Converting to oral phenytoin:
Convert to oral preparation when patient is able to tolerate feeds. Give total daily dose as a single dose.
Formulations of phenytoin are not bioequivalent:
100mg injection (phenytoin sodium) = 100mg capsule (phenytoin sodium)
100mg injection (phenytoin sodium) = 92mg liquid (phenytoin base)
100mg capsule (phenytoin sodium) = 92mg liquid (phenytoin base)
Contact pharmacy for advice regarding dose conversion between preparations.
Phenytoin suspension interacts with enteral feeds. Stop enteral feeds for two hours before and two hours
after giving phenytoin suspension to enhance absorption of phenytoin.
References and Provenance
BNF - January 2017 online version
Summary of product characteristics for Epanutin Ready Mixed Parenteral. Revision of text 29 July 2016
Summary of product characteristics for Phenytoin Hikma 05-Dec-2014
Injectable medicines guide (Medusa) 17 Jan 2017
UKCPA: Drug Dosing in Extremes of Body Weight in Critically Ill Patients. September 2013
Patient Safety Alert NHS/PSA/W/2016/010
Date produced: 01/2016 Valid until: 01/2019
Author: Tommaso Malavenda, Specialist Pharmacist,
Reviewed: Dave Abbott, Medicines Optimisation Pharmacist 1/2017
Quality Assurance Check by: Sumrah Shaffiq, Advanced Clinical Pharmacist
Produced by Clinical Pharmacy Services
For further information contact medicines.information@nhs.net ext 65377
This information has been prepared by Leeds Medicines Management and Pharmacy Services
for use by health care professionals at Leeds Teaching Hospitals NHS Trust
