Comparative Pharmacology
Head-to-head clinical analysis: EXTENDED PHENYTOIN SODIUM versus TOPAMAX.
Peer-Reviewed Evidence
Head-to-head clinical analysis: EXTENDED PHENYTOIN SODIUM versus TOPAMAX.
EXTENDED PHENYTOIN SODIUM vs TOPAMAX
Comparing the clinical profiles, pharmacokinetic behaviors, and safety indices of these two therapeutic agents.
Phenytoin stabilizes neuronal membranes by promoting sodium channel inactivation, reducing repetitive firing of action potentials, and decreasing synaptic transmission.
Antiepileptic; modulates voltage-gated sodium channels, enhances GABA-A activity, antagonizes AMPA/kainate glutamate receptors, weakly inhibits carbonic anhydrase.
Oral: 100 mg three times daily; intravenous: 10-20 mg/kg loading dose at a maximum rate of 50 mg/min, then 100 mg every 6-8 hours maintenance.
Initial dose 25 mg orally twice daily; titrate by 25-50 mg weekly to effective dose; usual maintenance dose 200-400 mg/day divided twice daily; maximum 1600 mg/day.
None Documented
None Documented
22–32 hours (mean 24 hours) in adults, dose-dependent due to saturable metabolism; may exceed 60 hours at high concentrations.
Terminal elimination half-life is 21 hours (range 18-23 hours). Linear pharmacokinetics. Half-life is prolonged in renal impairment (CrCl <70 mL/min: ~35 hours).
Primarily hepatic metabolism (CYP2C9/CYP2C19), with <5% excreted unchanged renally. Fecal excretion accounts for minor elimination.
Renal: ~70% (unchanged drug); remainder as metabolites. Biliary/fecal: minimal (<5%).
Category D/X
Category C
Anticonvulsant
Anticonvulsant