Patients should be cautioned against concomitant use of antacids and phenytoin. Consider using other options if possible. This is accomplished by reducing the amplitude of sodium-dependent action potentials through enhancing steady state inactivation. Sodium channels exist in three main conformations: Phenytoin 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 phenytoin sodium can produce voltage-dependent, use-dependent and time-dependent block of sodium-dependent action potentials. This includes the reduction of post-tetanic potentiation at synapses which prevents cortical seizure foci from detonating adjacent cortical areas.
Phenytoin reduces the maximal activity of brain stem centers responsible for the tonic phase of generalized tonic-clonic seizures. 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. In , outside scientists including H. Houston Merritt and Tracy Putnam discovered phenytoin's usefulness for controlling seizures , without the sedative effects associated with phenobarbital.
According to Goodman and Gilman's Pharmacological Basis of Therapeutics In contrast to the earlier accidental discovery of the antiseizure properties of potassium bromide and phenobarbital , phenytoin was the product of a search among nonsedative structural relatives of phenobarbital for agents capable of suppressing electroshock convulsions in laboratory animals.
Peak concentration is usually reached in hours. If using IV phenytoin, the patient should be on telemetry due to the risk of cardiac effects including dysrhythmias, hypotension, bradycardia and cardiac arrest. Onset of initial response is usually immediate. Peak concentration with a loading dose is usually reached in minutes.
Maintainence A typical maintainence dose is mg PO, which can be divided into twice daily dosing. Onset of initial response is generally days. The maintainence dose will need to be the dose at which the patient has maximal benefit i. Monitoring with serum phenytoin or free phenytoin levels will help with determining if the dose a patient is on is therapeutic, though ultimately, the patient's clinical condition is the most important factor to monitor.
Monitoring In general, assuming that the patient's seizures can be controlled with monotherapy: If the patient is having seizures, the dose is subtherapeutic. If the patient is toxic or having intolerable adverse effects, the dose is supratherapeutic.
Checking a phenytoin level can help with determining if a patient has a sufficient serum level of phenytoin that should be therapeutic. Levels should be checked after half-lives approximately days. Labs Total phenytoin level range:
Tags: atorvastatin winthrop 20 mg best way give prevacid solutabs cpt code for boniva injection xenical 120mg india
© Copyright 2017 Phenytoin weak base :: beccajhowell.com.