Posology : מינונים

2   DOSAGE AND ADMINISTRATION

General
Phenytoin capsules, are formulated with the sodium salt of phenytoin. The free acid form of phenytoin is used in the phenytoin suspensions (125 mg/5 mL). Because there is approximately an 8% increase in drug content with the free acid 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.

For all oral formulations, dosage should be individualized to provide maximum benefit. In some cases serum drug level determinations may be necessary for optimal dosage adjustments. Optimum control without clinical signs of toxicity occurs more often with serum levels between 10-20 mcg/mL, although some mild cases of tonic- clonic (grand mal) epilepsy may be controlled with lower serum levels of phenytoin.
With recommended dosage a period of seven to ten days may be required to achieve steady state drug levels with phenytoin, and changes in dosage (increase or decrease) should not be carried out at intervals shorter than seven to ten days.

Adult Dosage
Divided daily dosage:
For oral capsules, patients who have received no previous treatment may be started on 300 mg daily, to be taken in three equally divided doses, and the dosage then adjusted to suit individual requirements. For most adults, the satisfactory maintenance dosage will be 300 mg to 400 mg daily, to be taken in three to four equally divided doses respectively. An increase up to 600mg daily may be made if necessary.

Non-emergency oral loading dose in adult patients
An oral loading dose of phenytoin may be used for non-emergency initiation of therapy in adults who require rapid steady state serum levels, and for whom intravenous administration is not desirable. This dosing regimen should be reserved for patients in a clinic or hospital setting where phenytoin serum levels can be closely monitored.
Patients with a history of renal or liver disease should not receive the oral loading dose regimen.

The recommended oral loading dose is one gram of phenytoin divided into three doses (400 mg, 300 mg, 300 mg) and administered at two-hour intervals. Normal maintenance dosage is then instituted 24 hours after the loading dose, with frequent serum level determinations.

Pediatric Dosage
For oral capsules, initially, 5 mg/kg/day in two or three equally divided doses with subsequent dosage individualized to a maximum of 300 mg daily. A recommended daily maintenance dosage is usually 4 to 8 mg/kg.
Children over 6 years and adolescents may require the minimum adult dose (300 mg/day). If the daily dosage cannot be divided equally, the larger dose should be given at bedtime.