Absorption: Absorbed slowly from the GI tract. Bioavailability differs among products; the Dilantin and Phenytek preparations are considered to be "extended" products. Other products are considered to be prompt release.
Distribution: Distributes into CSF and other body tissues and fluids. Enters breast milk; crosses the placenta, achieving similar maternal/fetal levels. Preferentially distributes into fatty tissue.
Protein Binding: Adults 90–95%; ↓ protein binding in neonates (up to 20% free fraction available), infants (up to 15% free), and patients with hyperbilirubinemia, hypoalbuminemia, severe renal dysfunction or uremia.
Metabolism and Excretion: Mostly metabolized by the liver; minimal amounts excreted in the urine.
Half-life: 22 hr (range 7–42 hr).
TIME/ACTION PROFILE (anticonvulsant effect)
|PO||2–24 hr (1 wk)*||1.5–3 hr||6–12 hr|
|PO-ER||2–24 hr (1 wk)||4–12 hr||12–36 hr|
|IV||0.5–1 hr (1 wk)||rapid||12–24 hr|
*( ) = time required for onset of action without a loading dose
phenytoin has been found in Davis's Drug Guide
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