What is the dosage for Dilantin? The dosing of phenytoin is patient specific. It may be given once, twice, 3, or 4 times daily. Doses are often adjusted to find the optimal dose based on measurement of blood levels.
Taking phenytoin with food may reduce some of the side effects. Elderly patients, debilitated persons, and patients with certain kidney or liver diseases may need lower doses. The suspension should not be given at the same time as tube feedings since tube feedings bind to phenytoin and reduce its absorption.
The recommended adult dose is mg two to four times daily. Some patients may require mg three times daily. Patients with impaired liver function, elderly patients, or those who are gravely ill may show early toxicity.
Because the fraction of unbound phenytoin is increased in patients with renal or hepatic disease, or in those with hypoalbuminemia, the monitoring of phenytoin serum levels should be based on the unbound fraction in those patients. The lethal dose in adults is estimated to be 2 to 5 grams. The initial symptoms are nystagmus , ataxia , and dysarthria. Other signs are tremor , hyperreflexia, lethargy , slurred speech, blurred vision, nausea, and vomiting. The patient may become comatose and hypotensive.
Death is caused by respiratory and circulatory depression. There are marked variations among individuals with respect to phenytoin serum levels where toxicity may occur. Irreversible cerebellar dysfunction and atrophy have been reported. Treatment Treatment is nonspecific since there is no known antidote. The adequacy of the respiratory and circulatory systems should be carefully observed and appropriate supportive measures employed. Hemodialysis can be considered since phenytoin is not completely bound to plasma proteins.
Total exchange transfusion has been used in the treatment of severe intoxication in pediatric patients. In acute overdosage the possibility of other CNS depressants, including alcohol, should be borne in mind. Sinus bradycardia , sino- atrial block, second and third degree A-V block, and Adams-Stokes syndrome because of the effect of parenteral phenytoin on ventricular automaticity. Coadministration with delavirdine because of the potential for loss of virologic response and possible resistance to delavirdine or to the class of non-nucleoside reverse transcriptase inhibitors.
Pharmacokinetics Absorption A fall in serum levels may occur when patients are changed from oral to intramuscular administration. The drop is caused by slower absorption, as compared to oral administration, because of the poor water solubility of phenytoin.
Intravenous administration is the preferred route for producing rapid therapeutic serum levels. Patients stabilized on a daily oral regimen of DILANTIN experience a drop in peak blood levels to 50 to 60 percent of stable levels if crossed over to an equal dose administered intramuscularly.
However, the intramuscular depot of poorly soluble material is eventually absorbed, as determined by urinary excretion of 5- p-hydroxyphenyl phenylhydantoin HPPH , the principal metabolite, as well as the total amount of drug eventually appearing in the blood.
As phenytoin is highly protein bound, free phenytoin levels may be altered in patients whose protein binding characteristics differ from normal. A short-term one week study indicates that patients do not experience the expected drop in blood levels when crossed over to the intramuscular route if the DILANTIN IM dose is increased by 50 percent over the previously established oral dose.
To avoid drug accumulation caused by absorption from the muscle depots, it is recommended that for the first week back on oral DILANTIN, the dose be reduced to half of the original oral dose one-third of the IM dose. Experience for periods greater than one week is lacking and blood level monitoring is recommended. Distribution Phenytoin is extensively bound to plasma proteins and is prone to competitive displacement.
Elimination The serum half-life in man after intravenous administration ranges from 10 to 15 hours. Excretion Most of the drug is excreted in the bile as inactive metabolites. Urinary excretion of phenytoin and its metabolites occurs partly by glomerular filtration but, more importantly, by tubular secretion. Renal Or Hepatic Impairment Increased fraction of unbound phenytoin in patients with renal or hepatic disease, or in those with hypoalbuminemia has been reported.
Pregnancy It has been reported in the literature that the plasma clearance of phenytoin generally increased during pregnancy, reached a peak in the third trimester and returned to the level of pre-pregnancy after few weeks or months of delivery. Advise the patient that, because these signs and symptoms may signal a serious reaction, that they must report any occurrence immediately to a physician. Inform patients that certain over-the-counter medications e.
John's wort can alter their phenytoin levels. Gingival Hyperplasia Advise patients of the importance of good dental hygiene in order to minimize the development of gingival hyperplasia and its complications. When appropriate, counsel pregnant women and women of childbearing potential about alternative therapeutic options.
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.
Jack Dreyfus , founder of the Dreyfus Fund , became a major proponent of phenytoin as a means to control nervousness and depression when he received a prescription for Dilantin in He is believed[ by whom? This was partially because Parke-Davis was reluctant to invest in a drug nearing the end of its patent life, and partially due to mixed results from various studies.
The list identifies medications that the FDA has identified a potential safety issue, but does not mean that FDA has identified a causal relationship between the drug and the listed risk.
© Copyright 2017 Phenytoin alcohol interaction - Phenytoin levels may decrease when the suspension is given with enteral feedings. This could lead to a loss of seizure control. You could interrupt the feeding for 2 hours before and after the phenytoin dose. Alternatively, you may give the phenytoin suspension diluted in water and flush the tube with water after administration..