#phenytoin

Phenytoin and Its Impurities - Pharmaffiliates

Indication (What it’s used for):

Tonic-Clonic Seizures

Child (1 month to 11 years): Initially 1.5 mg/kg to 2.5 mg/kg twice daily, then adjusted according to response to 2.5 mg/kg to 5 mg/kg twice daily. Dose also adjusted according to plasma-phenytoin concentration. Maximum 300 mg per day [ORAL]

Child (12 to 17 years): Initially 75 mg to 150 mg twice daily, then adjusted according to response to 150 mg to 200 mg twice daily. Dose also adjusted according to plasma-phenytoin concentration [ORAL]

Adult: Initially 3 mg/kg to 4 mg/kg daily, alternatively 150 mg to 300 mg once daily, alternatively 150 mg to 300 mg daily in 2 divided dose; usual maintenance 200 mg to 500 mg daily. Dose adjusted according to response and plasma-phenytoin concentration [ORAL]

Focal Seizures

Child (1 month to 11 years): Initially 1.5 mg/kg to 2.5 mg/kg twice daily, then adjusted according to response to 2.5 mg/kg to 5 mg/kg twice daily. Dose also adjusted according to plasma-phenytoin concentration. Maximum 300 mg per day [ORAL]

Child (12 to 17 years): Initially 75 mg to 150 mg twice daily, then adjusted according to response to 150 mg to 200 mg twice daily. Dose also adjusted according to plasma-phenytoin concentration [ORAL]

Adult: Initially 3 mg/kg to 4 mg/kg daily, alternatively 150 mg to 300 mg once daily, alternatively 150 mg to 300 mg daily in 2 divided dose; usual maintenance 200 mg to 500 mg daily. Dose adjusted according to response and plasma-phenytoin concentration [ORAL]

Prevention and treatment of seizures during, or following, neurosurgery or severe head injury

Child: Initially 2.5 mg/kg twice daily, then adjusted according to response to 4 mg to 8 mg daily. Dose also adjusted according to plasma-phenytoin concentration. Maximum 300 mg per day [ORAL]

Adult: Initially 3 mg/kg to 4 mg/kg daily, alternatively 150 mg to 300 mg once daily, alternatively 150 mg to 300 mg daily in 2 divided dose; usual maintenance 200 mg to 500 mg daily. Dose adjusted according to response and plasma-phenytoin concentration [ORAL]

Status Epilepticus

Child (1 month to 11 years): Loading dose 20 mg/kg then 2.5 mg/kg to 5 mg/kg twice daily [IV]

Child (12 to 17 years): Loading dose 20 mg/kg then up to 100 mg 3 to 4 times a day [IV]

Adult: Loading dose 20 mg/kg, max 2 mg per dose, than maintenance 100 mg every 6 to 8 hours adjusted according to plasma-phenytoin concentration [IV]

Acute symptomatic seizures associated with head trauma or neurosurgery

Child (1 month to 11 years): Loading dose 20 mg/kg then 2.5 mg/kg to 5 mg/kg twice daily [IV]

Child (12 to 17 years): Loading dose 20 mg/kg then up to 100 mg 3 to 4 times a day [IV]

Adult: Loading dose 20 mg/kg, max 2 mg per dose, than maintenance 100 mg every 6 to 8 hours adjusted according to plasma-phenytoin concentration [IV]

Contraindication (When you can’t use it):

Acute Porphyria

2nd and 3rd degree Heart Block

Sino-atrial Block

Sinus Bradycardia

Stokes-Adams Syndrome

Cautions (When you need to be careful using it):

General

Enteral feeding

Pregnancy

IV

Heart failure

Hypotension

Injection solution alkaline

Respiratory Depression

Mechanism of Action (How it works):

Sodium Channel Blocker

Prevents the return of the sodiums channels to the active state by stabilizing the inactive form thereby preventing repetitive firing of the axons. Presynaptic and postsynaptic blockade of sodium channels of the axons causes stabilization of the neuronal membranes, blocks and prevents post-tetanic potentiation, limits the development of maximal seizure activity, and reduces the spread of seizures.

Side Effects:

General

Agranulocytosis

Bone Disorders

Confusion

Constipation

Drowziness

Eosinophilia

Gingival Hyperplasia

Hepatic Disorders

Hypersensitivity

Megaloblastic Anaemia

Nausea and Vomiting

Severe Cutaneous Adverse Reactions

Systemic Lupus Erythematosus

Oral

Electrolyte Imbalance

Vitamin D Deficiency

Pneumonitis

Parenteral

Arrthymia

Atrial Conduction Depression

Hypotension

Purple Glove Syndrome

Respiratory Disorders

Signs of Toxicity/Overdose:

Rash

Nystagmus

Diplopia

Slurred Speech

Ataxia

Confusion

Hyperglycaemia

Interactions:

Decreases exposure to Abacavir

Decreases exposure to Aldosterone Antagonists (e.g. Eplerenone)

Decreases exposure to Aminophylline

Decreases exposure to Azole Antifungals (e.g. Ketoconazole, Itraconazole)

Decreases exposure to Calcium Channel Blockers (e.g. Amlodipine, Felodipine)

Decreases efficacy of Combined Hormonal Contraceptives

Decreases exposure to Digoxin

Decreases exposure to Leukotriene Receptor Antagonists (e.g. Montelukast)

Amiodarone increases plasma-phenytoin concentration

Azole Antifungals (e.g. Miconazole, Fluconazole) increase plasma-phenytoin concentration

H2 Receptor Antagonists (e.g. Cimetidine) increase plasma-phenytoin concentration

Selective Serotonin Reuptake Inhibitors (e.g. Fluoxetine, Sertraline) increase plasma-phenytoin concentration

Acute Alcohol increases plasma-phenytoin concentration

St John’s Wort decreases plasma-phenytoin concentration

Rifampicin decreases plasma-phenytoin concentration

Chronic Alcohol  increases plasma-phenytoin concentration 

Monitoring:

Plasma-phenytoin concentration

Full blood count

Liver function tests

Points of Particular Interest:

Enzyme inducer so may affect the metabolism of other drugs

Should be prescribed/dispensed by brand as different brands may use different phenytoin salts leading to clinically significant differences in response

Should not be given within 2 hrs of enteral feeding

Sources:

BNF 78

Dilantin (also known as Phenytoin) is an anticonvulsant medicine applied to treat patients suffering from epilepsy or seizures.

Yet, scientists and class action attorneys have informed the public that long-term Phenytoin use may lead to birth defects and may cause serious medical complications that can permanently alter a person’s movement, speech, and coordination.

Generic Name: phenytoin

Trade Name: Dilantin

Therapeutic Class: Anticonvulsants

Pharmacologic Class: Hydantoin derivatives

Indicated Uses: Management of tonic-clonic (generalized) seizures and complex (partial) seizures.

Adverse Effects: Lethargy, abnormal movements, mental confusion, cognitive changes

Black Box Warning: Carefully monitor cardiac status during and after IV administration. CV toxicity may increase with infusion rates above those recommended. Toxicity has also been reported at or below recommended infusion rate. Reduction in administration or discontinuation of dosing may be needed.

Pregnancy Considerations: Drug may cause fetal harm. Drug may interact with hormone-containing contraceptives.

Nursing Considerations: Don’t stop drug suddenly because this may worsen seizures. Monitor drug level because of narrow therapeutic window.

Drug Interactions: Interacts with oral contraceptives, warfarin, diazepam, other seizure medications.