Manufacturer: Pfizer manufactures Dilantin Infatabs.


The uses of Dilantin Infatabs include:
Phenytoin is used to prevent and control seizures (also called an anticonvulsant or antiepileptic drug). It works by reducing the spread of seizure activity in the brain.


Dilantin is indicated for the control of grand mal and psychomotor seizures. Dilantin will prevent or effectively decrease the incidence and severity of convulsive seizures in a high percentage of cases, with patients exhibiting little tendency to become resistant to its action. Besides its effectiveness in controlling seizures, Dilantin frequently improves the mental condition and outlook of epileptic patients and there is also increasing evidence that Dilantin is valuable in the prevention of seizures occurring during or after neurosurgery and in the treatment of certain cardiac arrythmias. Phenytoin serum level determinations may be necessary for optimal dosage adjustments (see Dosage and Administration).

Dosage and Administration:

Dilantin capsules (30 mg, 100 mg) are formulated with the sodium salt of phenytoin.

The free acid form of phenytoin is used in Dilantin Infatabs (50 mg) and Dilantin Paediatric Suspension (30 mg/5 mL).

Because there is approximately an 8% increase in drug content with the free form over that of the sodium salt, dosage adjustments and serum level monitoring may be necessary when switching from a product formulated with the free acid to a product formulated with the sodium salt and vice versa.


Dosage should be individualised to obtain maximum benefit. In some cases, serum blood level determinations may be necessary for optimal dosage adjustments. Serum levels between 10 and 20 g/mL are considered to be clinically effective. With the recommended dosage, a period of at least 7 to 10 days may be required to achieve therapeutic blood levels of Dilantin, unless therapy is initiated with a loading dose. After the initial dose has been prescribed, plasma levels should be determined and the dosage adjusted if necessary to obtain a level in the therapeutic range; 10 to 20 g/mL (40 to 80 moles/L). Because phenytoin is hydroxylated in the liver by an enzyme system which is saturable, at high plasma levels small incremental doses may increase the half-life and produce very substantial increases in serum levels, when these are in the upper range.

Oral Administration

Although phenytoin has a relatively long plasma half-life, thrice daily dosing may reduce the incidence of gastric irritation since lower doses can be administered with thrice daily dosing as compared with twice daily dosing. Recent studies suggest that a better correlation is achieved between plasma levels and dose by expressing the latter on a body-weight basis.


Initiate therapy with 4 to 5 mg/kg/day in 2 to 3 divided doses and assess plasma levels. A further upward dosage adjustment may be required to a maximum of 600 mg/day, dosage increments should be made at about 2 week intervals. Plasma phenytoin levels should be monitored should higher doses be required.

An initial dose of 6 to 7 mg/kg/day would be more likely to ensure therapeutic levels however, there is a risk that such a dose may achieve levels exceeding 20 g/mL and increase the risk of toxicity.


Initiate therapy with 5 mg/kg/day in 2 to 3 equally divided doses not to exceed 300 mg daily. A recommended daily maintenance dosage is usually 4 to 8 mg/kg. Children over 6 years may require the minimum adult dose (300 mg/day).

Paediatric dosage forms available include Dilantin Chewable Infatabs and Dilantin Paediatric Suspension.