Most recent guideline publication: Clinical Pharmacogenetics Implementation Consortium (CPIC) Guidelines for CYP2C9 and HLA-B Genotype and Phenytoin Dosing (November 2014) Updates since publication: No updates on dosing recommendations since publication. Clinical features of phenytoin overdose include neurological and gastrointestinal symptoms. Often doses are arbitrarily “capped” for fear of overdosing. You must take them 2 or 3 times per day. If needed, in the acute setting phenytoin should have additional doses given prior to six hours after the loading dose to achieve therapeutic CSF levels. Onset of symptoms is usually within 1 to 2 hours of ingestion, or within minutes if IV administration. IV loading dose For phenytoin-naïve patients, loading doses can be calculated as follows: Weight (kg) Dose (mg/mL) 40-49 750mg in 100mL Clinical Guideline for the Use of Phenytoin in Epilepsy V1.0 Page 6 of 15 3. The dose is the same for all phenytoin products when initiating therapy. Adjust phenytoin dosing based on values. I’m sorry, I don’t have a good explanation or rationale for why that is (given its extensive Vd), but we just have to go with it. Fosphenytoin is indicated for the control of generalized convulsive status epilepticus and to prevent and treat seizures occurring during neurosurgery, when other means of phenytoin administration are unavailable, inappropriate, or deemed less advantageous. 3. Pod 3: Phenytoin Dosing and Dosing Weight In general, phenytoin is dosed based on ideal (aka lean) body weight. Alternatively, free phenytoin and total phenytoin levels drawn at the same time. IV loading dose For phenytoin-naïve patients, loading doses can be calculated as follows: Weight (kg) Dose (mg/mL) 40-49 750mg in 100mL Phenytoin is a commonly used medication for the treatment of status epilepticus and acute seizure control in the emergency department (ED).

1, – 5 However, phenytoin dosing can pose a challenge to clinicians because of its narrow therapeutic range and nonlinear pharmacokinetic profile. Dosing and administration of injectable phenytoin. phenytoin are non-linear, therefore a small dose increase can produce a large increase in phenytoin levels. Dosing of phenytoin orally or via nasogastric/feeding tube 4. Tables and figure provided in the main manuscript of the guideline: Table 1. 2.

These patients also tend to have low serum albumin.
Because phenytoin has demonstrated some saturable and erratic oral absorption beyond 400 mg, the use of large oral loading doses is controversial. Scenarios where monitoring levels may be clinically useful include: (1) establishing an Clinical Guideline for the Use of Phenytoin in Epilepsy V1.0 Page 6 of 15 3. UW Health Guidelines for the Dosing of Medications in Patients Receiving Continuous Enteral Feedings Lactation: Phenytoin is secreted in human milk; developmental and health benefits of breastfeeding should be considered along with mother’s clinical need for therapy and any potential adverse effects on breastfed infant from phenytoin or from underlying maternal condition.

Concomitant use of valproic acid and some other drugs displaces phenytoin from plasma proteins and can lead to erratic levels. Table 1: Expected Increase in Phenytoin Concentration with “Once Only” Top-Up Dosing Increase in Concentration Patient's weight Dose 50 kg 60 kg 70 kg 80 kg 200mg 6 mg/L 5 mg/L 4 mg/L 3.5 mg/L patient with a measured phenytoin concentration of 5mg/L could be given a single top-up dose of 750mg to achieve a concentration of 20mg/L. Phenytoin dosing Use the red supplementary drug chart for an IV prescription. Phenytoin sodium 'top-up' dose (mg) = (20 - measured concentration (mg/L)) x 0.7 x wt (kg) Table 2 gives the approximate increase in concentration following doses of 250–750mg.