Drug information of Phenytoin

Phenytoin

Drug group: Anticonvulsants

Phenytoin is an anti-epileptic drug, also called an anticonvulsant. It works by slowing down impulses in the brain that cause seizures. Phenytoin is used to control seizures. Phenytoin does not treat all types of seizures, and your doctor will determine if it is the right medicine for you.

Mechanism of effect

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, phenytoin 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. Loss of post tetanic potentiation prevents cortical seizure foci from detonating adjacent cortical areas. Phenytoin reduces the maximal activity of brain stem centers responsible for the tonic phase of tonic-clonic (grand mal) seizures.

Pharmacodynamic

Phenytoin is an antiepileptic drug which can be useful in the treatment of epilepsy.

Pharmacokinetics

Bioavailability 70-100% oral, 24.4% rectal. Rapid rate of absorption with peak blood concentration expected in 1½ to 3 hours. Highly protein bound, 90% Metabolism:Primarily hepatic. Most of the drug is excreted in the bile as inactive metabolites which are then reabsorbed from the intestinal tract and excreted in the urine. Urinary excretion of phenytoin and its metabolites occurs partly with glomerular filtration but, more importantly, by tubular secretion. Half life:22 hours (range of 7 to 42 hours)

Drug indications

Status Epilepticus , Seizures

Dosage

Usual Adult Dose for Seizures
EXTENDED RELEASE FORMULATION (100 mg per capsule):
-DIVIDED DAILY DOSAGE:
Initial dose (in patients not previously treated with this drug): 1 capsule orally 3 times a day; dosage then adjusted to suit individual requirements
Maintenance dose: For most adults the satisfactory maintenance dosage will be 1 capsule 3 to 4 times a day; for others an increase up to 2 capsules 3 times a day may be made, if necessary
-ONCE-A-DAY DOSAGE:
If seizure control is established with divided doses of 3 capsules orally daily, then 300 mg orally once a day may be considered
-LOADING DOSE:
Some clinicians use an oral loading dose in adults who require rapid steady-state serum levels and where IV administration is not desirable. This dosing regimen should be reserved for patients in a clinic or hospital setting where phenytoin serum levels can be closely monitored. Patients with a history of renal or liver disease should not receive the oral loading regimen: Initially, 1 gm is divided into 3 doses (400 mg, 300 mg, 300 mg) and administered at 2 hour intervals. Normal maintenance dosage is then instituted 24 hours after the loading dose, with frequent serum level determinations.
CHEWABLE TABLETS (50 mg per tablet):
Initial dose (in patients not previously treated with this drug): 2 tablets chewed 3 times a day; dosage then adjusted to suit individual requirements; for most adults, the satisfactory maintenance dosage will be 6 to 8 tablets daily; an increase to 12 tablets daily may be made, if necessary
SUSPENSION (125 mg per 5 mL):
Initial dose (in patients not previously treated with this drug): 5 mL orally 3 times daily; dosage then adjusted to suit individual requirements; an increase to 25 mL orally daily may be made, if necessary
Use: For the control of tonic-clonic (grand mal) and psychomotor (temporal lobe) seizures
Usual Pediatric Dose for Seizures
-ORAL:
Initial dose: 5 mg/kg/day orally in 2 or 3 equally divided doses, with subsequent dosage individualized to a maximum of 300 mg orally daily
-Maintenance dose: 4 to 8 mg/kg. Children over 6 years old and adolescents may require the minimum adult dose (300 mg/day)
Use: For the control of tonic-clonic (grand mal) and psychomotor (temporal lobe) seizures

Interactions

Atracurium , Atomoxetine , Albendazol , Amlodipine/Atorvastatine , Aprepitant , Ethosuximide , Ethinyl estradiol+ drospirenone , Adefovir , Ergotamine-C , Erlotinib , Erythromycin , Esomeprazole , Acetazolamide , Acetaminophen , Exemestane , Everolimus , Expectorant , Ipratropium bromide , Irinotecan , Isoflurane , Ifosfamide , Imatinib , intralipid , Buspirone , Bismuth , Pantoprazole , Paclitaxel , Tadalafil , Tacrolimus , Tetracycline , Tetracosactid , Trazodone , Triamcinolone , Temozolomide , Topotecan , Topiramate , Tinidazole , Thiothixene , Ticlopidine , Doxycycline , Deflazacort , Dopamine , Diazoxide , Dydrogesterone , Disopyramide , Rabeprazole , Zolpidem , Sunitinib , Sorafenib , Sulfadiazine , Ciprofloxacin , Cyclosporine , Fludrocortisone , Fluvoxamine , Fluoxetine , Diazepam , Warfarin , Folinic acid , Folic acid , Gabapentin , Glibenclamide , Lamotrigine , Lapatinib , Levamisole , Levonorgestrol , Mebendazol , Methotrexate , Methylprednisolone , Modafinil , Medroxyprogesterone , acitretin , Nilotinib , Valproate sodium , Vigabatrin , Vinblastin , Vincristin , Capecitabine , Chloramphenicol , Chlorpromazine , Clozapine , Contraceptive DE , Cotrimoxazole , Enzalutamide , Diltigel , Flecainide , Disulfiram , Bisoprolol , Daclatasvir , Clofazimine , Ranolazine , Praziquantel , Darunavir , Vecuronium , Caspofungin , Donepzil , Buprenorphine , Sodium Oxybate , Glipizide , Prochlorperazine , Quinidine , fluvastatin , Oxycodone , methylene blue , Ethinyl Estradiol , Axitinib , Apixaban , Ivabradine , Phenindione , Mifepristone , Afatinib , Indinavir , Dofetilide , Sarilumab , Doxifluridine , Endometrine , Dexmethylphenidate , Mitiglinide , Felbamate , Butalbital and Acetaminophen , Rocuronium , brigatinib , Abiraterone , Peginterferon alfa-2b , Parecoxib , Lumefantrine / artemether , Canagliflozin , Dienogest , Acemetacin , Copanlisib , Leucovorin , Telaprevir , Simeprevir , lumacaftor and Ivacaftor , Ulipristal , Etravirine , Dabrafenib , Dolutegravir , Acalabrutinib , Maraviroc , Nintedanib , cobicistat , Delavirdine , Sofosbuvir and velpatasvir , Fostamatinib , Apremilast , Palbociclib , Tasimelteon , trabectedine , Duvelisib , Floxuridine , tezacaftor/ivacaftor , Alpelisib , Triclabendazole , Lercanidipine , Edoxaban , Darolutamide , Quazepam , cosyntropin , Temsirolimus , ELBASVIR/GRAZOPREVIR , Lorlatinib , Larotrectinib , gilteritinib , glasdegib , Abemaciclib , Nitrendipine , Triphasic , Eliglustat , Elvitegravir , Suvorexant , rilpivirine , tolvaptan , Aminophenazone , bedaquiline , Gefitinib , Dasatinib , Remdesivir , neratinib , Cannabidiol , vemurafenib , vorapaxar , rolapitant , vortioxetine , voxelotor , dichlorphenamide , stiripentol , tecovirimat , Brivaracetam , Artesunate , Avapritinib , Netupitant , secukinumab , Ombitasvir, Paritaprevir, and Ritonavir , Capmatinib , Bromazepam , Dienestrol

Alerts

1-When, in the judgment of the clinician, the need for dosage reduction, discontinuation, or substitution of alternative anticonvulsant medication arises, this should be done gradually.
2-Antiepileptic drugs (AEDs), including phenytoin sodium, increase the risk of suicidal thoughts or behavior in patients taking these drugs for any indication.
3-Serious and sometimes fatal dermatologic reactions, including toxic epidermal necrolysis (TEN) and Stevens-Johnson syndrome (SJS), have been reported with phenytoin treatment
4-caution should be exercised in using this medication in patients suffering from Porphyria, impaired liver function,elderly patients, or those who are gravely ill ,diabet

Points of recommendation

1-Patients should also be cautioned on the use of other drugs or alcoholic beverages without first seeking the physician’s advice.
2-Patients should be made aware of the early toxic signs and symptoms of potential hematologic, dermatologic, hypersensitivity, or hepatic reactions.

Pregnancy level

D


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