Various formulation factors may affect the bioavailability of phenytoin; however, non-linear techniques have estimated absorption to be essentially complete. In adults, 300-500 mg given in divided daily doses have been reported in the literature. The efficacy of hormonal contraception may be diminished for women taking CYP-450 enzyme inducing AEDs, such as phenobarbital, phenytoin, carbamazepine and topiramate. Phenytoin is not indicated for seizures due to hypoglycaemia or other metabolic causes.Abrupt withdrawal of phenytoin in epileptic patients may precipitate status epilepticus. Accordingly, at the first sign of acute toxicity, serum drug level determinations are recommended. Phenytoin is highly protein bound and extensively metabolised by the liver. Reactions include nystagmus, ataxia, slurred speech, decreased co-ordination, mental confusion. 3.2. Healthcare professionals are asked to report any suspected adverse reactions via the Yellow Card Scheme at: www.mhra.gov.uk/yellowcard or search for MHRA Yellow Card in the Google Play or Apple App Store.The lethal dose in children is not known. Advise women of childbearing potential who are not planning a pregnancy to use effective contraception while using extended phenytoin sodium capsules, keeping in mind that there is a potential for decreased hormonal contraceptive efficacy [see Drug Interactions (7.2)]. Individual drug labels should be consulted.Acute alcohol intake may increase phenytoin serum levels while chronic alcoholism may decrease serum levels.Drugs whose serum levels and/or effects may be altered by phenytoin.a This list is not intended to be inclusive or comprehensive.
As elderly patients tend to receive multiple drug therapies, the possibility of drug interactions should be borne in mind. Dia Y.
• Phenytoin may cause a slight decrease in serum levels of total and free thyroxine, possibly as a result of enhanced peripheral metabolism.
Furthermore, the metabolism of phenytoin may be depressed. If we would like to use your name, we will email you to get your permission.Epilepsy Action is a charity that improves the lives of everyone affected by epilepsy.
Back DJ. Dosage should normally be adjusted according to serum levels where assay facilities exist.The clinically effective dose has not been established in clinical trials. Acute hepatic failure, toxic hepatitis and liver damage (see Section 4.4 Special warnings and precautions for use – Hepatic Injury).Dermatological manifestations sometimes accompanied by fever have included scarlatiniform or morbilliform rashes.
Dizziness, vertigo, insomnia, transient nervousness, motor twitchings, taste perversion headache, paraesthesia and somnolence have also been observed.
This site uses cookies. The clinical significance of these rodent tumours is unknown.Genetic toxicity studies showed that phenytoin was not mutagenic in bacteria or in mammalian cells in vitro. Rosenfeld WE,
Total exchange transfusion has been utilised in the treatment of severe intoxication in children.In acute overdosage the possibility of the presence of other CNS depressants, including alcohol, should be borne in mind.Pharmacotherapeutic group: Antiepileptics; Hydantoin derivativesPhenytoin is effective in various animal models of generalised convulsive disorders, reasonably effective in models of partial seizures but relatively ineffective in models of myoclonic seizures.It appears to stabilise rather than raise the seizure threshold and prevents spread of seizure activity rather than abolish the primary focus of seizure discharge.The mechanism by which phenytoin exerts its anticonvulsant action has not been fully elucidated however, possible contributory effects include:- Non-synaptic effects to reduce sodium conductance, enhance active sodium extrusion, block repetitive firing and reduce post-tetanic potentiation- Post-synaptic action to enhance gaba-mediated inhibition and reduce excitatory synaptic transmission- Pre-synaptic actions to reduce calcium entry and block release of neurotransmitter.Phenytoin is absorbed from the small intestine after oral administration. Klosterkov Jensen P, Dosing should be adjusted based on clinical response.
However, in the event of an allergic or hypersensitivity reaction, rapid substitution of alternative therapy may be necessary. Patients (and caregivers of patients) should be advised to seek medical advice should signs of suicidal ideation or behaviour emerge.Cases of bradycardia and asystole/cardiac arrest have been reported, most commonly in association with phenytoin toxicity (see Section 4.9), but also at recommended phenytoin doses and levels.Hypersensitivity Syndrome (HSS) or Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS) has been reported in patients taking anticonvulsant drugs, including phenytoin. 234343) and a company limited by guarantee (No.
Used with permission.Clinical Inquiries provides answers to questions submitted by practicing family physicians to the Family Physicians Inquiries Network (FPIN).
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