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Phenytoin Dosing for Adults

Refer to the following table for the recommended phenytoin starting doses for adults:
Phenytoin Product
Starting Adult Dosage
Phenytoin extended-release capsules (Dilantin Kapseals)
100 mg three times daily or 300 mg once daily
Phenytoin chewable tablets (Dilantin Infatabs)
100 mg (two tablets) three times daily
Phenytoin oral suspension (Dilantin-125)
125 mg (5 mL or 1 teaspoonful) three times daily
Most likely, your healthcare provider will measure the amount of phenytoin in your blood (using a blood test) and adjust your dose as necessary. Because it takes a while for the medication to build up in your system, this blood test is most useful 7 to 10 days after starting phenytoin or changing your dose (when you have reached a steady phenytoin level). In emergencies, your healthcare provider may start you at a higher phenytoin dosage.

Phenytoin Dosing for Children

For children, the starting phenytoin dose is based on weight: phenytoin 5 mg per kg per day (about 2.3 mg per pound of body weight each day), divided into two or three doses per day. The starting dose is the same for all phenytoin products. Most likely, your child's healthcare provider will measure the amount of phenytoin in your blood (using a blood test) after a week or two and adjust your child's dose as necessary. In emergencies, your child's healthcare provider may start your child with a higher phenytoin dose.
Written by/reviewed by:
Last reviewed by: Kristi Monson, PharmD;
Last updated/reviewed:
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