Mechanism of action The mechanism of action of<unk>  sodium. Sodium channels are: 1) Closed 2) Open 3) Inactive<unk>  effect)<unk>  is believed to protect against seizures by causing voltage-dependent block of voltage gated sodium channels. This blocks sustained high frequency repetitive firing of action potentials. This is accomplished by reducing the amplitude of sodium-dependent action potentials through enhancing steady-state inactivation. Sodium channels exist in three main conformations: the resting state, the open state, and the inactive state.<unk>  binds preferentially to the inactive form of the sodium channel. Because it takes time for the bound drug to dissociate from the inactive channel, there is a time-dependent block of the channel. Since the fraction of inactive channels is increased by membrane depolarization as well as by repetitive firing, the binding to the inactive state by<unk>  sodium can produce voltage-dependent, use-dependent and time-dependent block of sodium-dependent action potentials. The primary site of action appears to be the motor cortex where spread of seizure activity is inhibited. Possibly by promoting sodium efflux from neurons,<unk>  tends to stabilize the threshold against hyperexcitability caused by excessive stimulation or environmental changes capable of reducing membrane sodium gradient. This includes the reduction of post-tetanic potentiation at synapses which prevents cortical seizure foci from detonating adjacent cortical areas.<unk>  reduces the maximal activity of brain stem centers responsible for the tonic phase of generalized tonic-clonic seizures. Pharmacokinetics<unk>  elimination kinetics show mixed-order, non-linear elimination behaviour at therapeutic concentrations. Where<unk>  is at low concentration it is cleared by first order kinetics, and at high concentrations by zero order kinetics. A small increase in dose may lead to a large increase in drug concentration as elimination becomes saturated. The time to reach steady state is often longer than 2 weeks.
Phenytoin
Mephenytoin
Carbamazepine
Mesuximide
Propazepine
Levetiracetam
Phenobarbital
Oxcarbazepine