Epanutin injection (Phenytoin)
How does it work?
Epanutin injection contains the active ingredient phenytoin, which is a type of medicine called an anticonvulsant. (NB. Phenytoin is also available without a brand name, ie as the generic medicine.) Phenytoin is used to treat epilepsy and works by stabilising electrical activity in the brain.
The brain and nerves are made up of many nerve cells that communicate with each other through electrical signals. These signals must be carefully regulated for the brain and nerves to function properly. When abnormally rapid and repetitive electrical signals are released in the brain, the brain becomes over-stimulated and normal function is disturbed. This can result in fits or seizures.
Phenytoin controls seizures by preventing the excessive electrical activity in the brain. It is thought to achieve this by preventing sodium from entering nerve cells when they begin to fire rapid and repetitive electrical signals. A build up of sodium in the nerve cells is necessary for the electrical signal to build up and be passed on to other nerve cells. As phenytoin prevents this, it helps stabilise the electrical activity in the brain.
Phenytoin is given by injection or drip into a vein to control repeated seizures.
What is it used for?
- Epilepsy. Phenytoin injection is used to control repeated seizures of the generalised tonic-clonic type, where there is no recovery of conciousness between seizures (status epilepticus).
- Seizures associated with brain surgery or head injury.
- Irregular heart beats (arrhythmias), when other medicines are not effective.
- Different people can vary widely in the way their bodies respond to and metabolise phenytoin. This can also be affected by many other medicines (see end of factsheet for more details). As a result, your phenytoin dose will need to be individualised. Your doctor may need to take blood tests from time to time to check the amount of phenytoin in your blood.
- If the level of phenytoin in your blood gets too high, it can cause symptoms such as confusion, rapid involuntary eye movements, blurred vision, slurred speech or clumsy movements. You should tell your doctor if you experience any of these symptoms, so that your blood level of phenytoin can be measured and your dose reduced if necessary.
- If you get a skin rash or other signs of allergic reaction during treatment with this medicine, such as a fever or swollen glands, you should inform your doctor immediately.
Use with caution in
- Elderly people.
- Extremely ill people.
- Low blood pressure (hypotension).
- Heart failure.
- Decreased liver function.
- High levels of urea in the blood (uraemia).
- Hereditary blood disorders called porphyrias.
- People of Thai or Han Chinese ethnic origin.
Not to be used in
- Slow heart rate caused by the pacemaker of the heart (sinus bradycardia).
- Defect of the heart's electrical message pathways resulting in decreased function of the heart (sino-atrial block, or 2nd or 3rd degree heart block).
- A syndrome characterised by attacks of temporary loss of conciousness that happen when the blood flow stops due to problems with the heart beat (Adams-Stokes syndrome).
This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy. If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.
Pregnancy and breastfeeding
Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.
- Pregnant women treated with antiepileptic medicines such as phenytoin have a higher risk of carrying a baby with developmental problems and malformations. However, if a pregnant woman experiences repeated fitting (status epilepticus) it is vital that this is controlled as quickly as possible, because the seizures can stop the oxygen supply to the baby. It is important that all the risks and benefits of treatment are weighed up. Seek medical advice from your doctor.
- This medicine passes into breast milk. The manufacturer recommends that women being treated with this medicine should avoid breastfeeding their infants and bottlefeed instead. Seek medical advice from your doctor.
Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Just because a side effect is stated here does not mean that all people using this medicine will experience that or any side effect.
- Rapid involuntary movements of the eyes (nystagmus).
- Shaky movements and unsteady walk (ataxia).
- Slurred speech.
- Decreased co-ordination.
- Pins and needles sensations.
- Difficulty sleeping (insomnia).
- Nausea and vomiting.
- Skin rashes.
- Disturbances in the normal numbers of blood cells in the blood.
- Liver problems.
- Increased hair growth (hirsutism).
- Enlargement of the gums or lips.
- Coarsening of facial features.
- Irritation, inflammation or tenderness at the injection site.
- Phenytoin injection can cause severe problems with heart function or breathing.
The side effects listed above may not include all of the side effects reported by the medicine's manufacturer. For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.
How can this medicine affect other medicines?
Phenytoin can interact with many medicines and the dose of phenytoin or the interacting medicine may need to be altered as a result. It is important that your doctor knows what medicines you are taking, including herbal medicines and non-prescription medicines, before phenytoin treatment is started. Likewise, once you are being treated with phenytoin it is important to check with your doctor or pharmacist before you stop taking any existing medicines, or start taking any new medicines, including herbal medicines and those bought without a prescription.
The following medicines may reduce the breakdown of phenytoin in the body. As this could increase the level of phenytoin in your blood and may increase the risk of side effects, your doctor may need to decrease your phenytoin dose if you are prescribed any of these:
- benzodiazepines, eg diazepam or chlordiazepoxide
- phenothiazines, eg chlorpromazine, prochlorperazine, thioridazine (these may also decrease the blood level of phenytoin)
- sulphonamides, eg co-trimoxazole, sulfamethoxazole, sulfadiazine
The following medicines may increase the breakdown of phenytoin in the body. As this could decrease the level of phenytoin in your blood and may make it less effective, your doctor may need to increase your phenytoin dose if you are prescribed any of these:
- folic acid
- the herbal remedy St John's wort (Hypericum perforatum) - this should not be taken by people who are taking phenytoin
The effects of phenytoin on other anticonvulsant medicines, and of other anticonvulsants on phenytoin, are fairly unpredictable. If more than one anticonvulsant is being used at the same time, the blood levels of the medicines, their effect on seizures, and the emergence of side effects should be well monitored.
Chemotherapy medicines used to treat cancer can affect the blood level of phenytoin. Your phenytoin blood level should be monitored if you have chemotherapy.
Phenytoin may may increase the breakdown of the following medicines in the body. As this could decrease the level of these medicines in the blood and may make them less effective, your doctor may need to prescribe a larger than normal dose of these:
- antifungal medicines, eg fluconazole, ketoconazole, itraconazole, voriconazole
- calcium channel blockers, eg felodipine, nimodipine, verapamil
- corticosteroids, eg dexamethasone, fludrocortisone, methylprednisolone, prednisolone
- efavirenz (this may also affect the blood level of phenytoin)
- oestrogens and progestogens such as those in the contraceptive pill (Phenytoin can make these types of contraceptive ineffective, or cause breakthrough bleeding. Women taking phenytoin who need a contraceptive should be prescribed hormonal contraceptives that contain a total of at least 50 micrograms of oestrogen, or use non-hormonal methods of contraception, such as condoms. Discuss this with your doctor.)
- oestrogens and progestogens in HRT (hormone replacement therapy)
- protease inhibitors, eg ritonavir, lopinavir, indinavir (these may also affect the blood level of phenytoin)
- vitamin D.
Phenytoin may increase the anti-blood-clotting effect of the anticoagulant medicine warfarin. If you are being treated with phenytoin in combination with warfarin your blood clotting time (INR) should be regularly monitored, particularly when starting or stopping treatment and after any dose changes.
Other medicines containing the same active ingredient
Phenytoin tablets and injection are also available without a brand name, ie as the generic medicine.