Indications
Fosphenytoin Sodium is an anti-seizure medicine given by injection. It is used to treat generalised convulsive status epilepticus (a prolonged seizure or repeated seizures without recovery in between), to prevent and treat seizures during or after brain surgery or head injury, and as a short-term replacement for Phenytoin capsules when a person cannot take medicines by mouth.
How It Works
Fosphenytoin is a prodrug: after injection, the body quickly converts it into Phenytoin. Phenytoin calms over-active nerve cells in the brain by blocking sodium channels, which stops the rapid repeated firing that causes seizures. Fosphenytoin is more water-soluble and gentler on veins than Phenytoin injection, and can also be given into a muscle.
Dosage and Administration
Fosphenytoin is given only by a doctor or nurse in hospital, as a slow infusion into a vein or as an injection into a muscle. Doses are written as phenytoin sodium equivalents (PE) and are calculated from body weight and the reason for use, exactly as prescribed. It must be infused slowly because fast injection can cause dangerous low blood pressure and heart rhythm problems; heart rate, blood pressure and breathing are monitored during and after the infusion. Blood levels of phenytoin are checked to guide further doses.
Interactions
Phenytoin has many interactions. It can reduce the effect of medicines such as Warfarin (may also increase it), hormonal contraceptives, Carbamazepine, Valproate, Lamotrigine, corticosteroids, some HIV medicines and Doxycycline. Medicines such as Amiodarone, Fluconazole, Isoniazid, Omeprazole and Sodium Valproate can raise phenytoin levels, while Carbamazepine and Rifampicin can lower them. Tell the doctor about every medicine, including herbal products.
Contraindications
- Allergy to Fosphenytoin, Phenytoin or other hydantoins
- Slow heart rate (sinus bradycardia), sino-atrial block, second or third degree heart block, or Adams-Stokes syndrome
- Use with Delavirdine
- Previous liver injury caused by Fosphenytoin or Phenytoin
Side Effects
Common effects include itching, burning or tingling (especially in the groin area) during the infusion, dizziness, drowsiness, unsteady walking, jerky eye movements (nystagmus), headache, nausea and pain at the injection site. Low blood pressure and slow or irregular heartbeat can occur, especially with fast infusion. Serious skin reactions such as Stevens-Johnson syndrome can occur; the risk is higher in people of Asian origin who carry the HLA-B*1502 gene.
Get urgent medical help, or tell the nurse at once, for chest pain, fainting, a very slow or irregular heartbeat, difficulty breathing, swelling of the face, a rash with blisters or peeling skin, or pain, swelling and colour change of the hand or arm near the injection.
Pregnancy and Lactation
Phenytoin can cause birth defects and bleeding problems in newborns, but uncontrolled seizures are also dangerous for mother and baby, so it is used in pregnancy only when the doctor decides it is needed; vitamin K may be given to the mother before delivery and to the newborn. Small amounts pass into breast milk; breastfeeding is usually possible with monitoring of the baby, after discussion with the doctor.
Precautions and Warnings
Use with care in liver or kidney disease, low blood albumin, heart disease, diabetes and porphyria. Elderly patients may need lower doses. Stopping phenytoin suddenly can trigger seizures. The phosphate in the medicine should be considered in people with severe kidney disease. Drowsiness may affect driving.
Overdose
Signs include drowsiness, jerky eye movements, slurred speech, unsteadiness, nausea, low blood pressure, heart rhythm problems and coma. Treatment is supportive in hospital with heart monitoring.
Therapeutic Class
Anticonvulsant (antiepileptic); hydantoin derivative, prodrug of Phenytoin.
Storage
Store in a refrigerator at 2 to 8°C, do not freeze. Hospital storage as directed on the pack. Keep out of the reach of children.
Prepared by the Oshud Alo team from standard drug references. For information only; always follow your doctor's advice.