NAPLEX Practice Question # 24

NAPLEX Examination.

Practice Question # 24.



Phenytoin (Dilantin) NAPLEX Review

Mechanism of action

(1) Phenytoin inhibits the spread of seizures at the motor cortex and blocks posttetanic potentiation by infl uencing synaptic transmission. Th ere is an alternation of ion fl uxes in depolarization, repolarization, and membrane stability phase and alternating calcium uptake in presynaptic terminals.

(2) Phenytoin is eff ective for the treatment of generalized tonic–clonic (grand mal) seizures and for partial seizures, both simple and complex. It is not eff ective for absence seizures.

Administration and dosage

(1) Th e usual daily dose for adults is 300 to 700 mg, with adjustments made as needed.

(a) Regular daily doses above 500 mg are poorly tolerated.

(b) A loading dose of 900 mg to 1.5 g may be given intravenously (IV). Th e infusion rate should not exceed 50 mg/min. (Alternatively, an oral loading dose may be given.)

(2) Th e usual daily dose for children is 4 to 7 mg/kg divided every 12 hrs. An IV loading dose of 15 mg/kg may be given.

(3) Phenytoin sodium is available as capsules and parenteral solution. Phenytoin is available as tablets and oral suspension.

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