Phenytoin
| Uses: | tonic clonic, focal seizures |
|---|---|
| Mechanism of action | prevents discharge of seizure activity Proposed mechanisms: 1. ↓ sodium conductance, enhance active sodium extrusion, block repetitive firing and reduce post-tetanic potentiation 2. Post-synaptic action to enhance gaba-mediated inhibition and reduce excitatory synaptic transmission 3. Pre-synaptic actions to reduce calcium entry |
| Dose | Loading for status: 20mg/kg (adults), max 2g in one dose |
| Pharmacokinetics | Absorption PO Distribution 90% protein bound Metabolism hydroxylation in liver Elimination |
| Time course of action | |
| Adverse effects | - common: gingival hyperplasia (secondary to increased expression of platelet derived growth factor, PDGF), hirsutism, coarsening of facial features, drowsiness - megaloblastic anaemia (secondary to altered folate metabolism) - peripheral neuropathy - enhanced vitamin D metabolism causing osteomalacia - lymphadenopathy - dyskinesia |
toxicity
Comes from its Na channel blocker effects
- clinical presentation: dose dependent CNS effects