Phenytoin

What is phenytoin?

Phenytoin is a prescription-only anticonvulsant (antiepileptic) medicine used to prevent and control seizures. It is available under brand names such as Epanutin, and comes in several forms including tablets, capsules, Infatabs (chewable tablets), oral suspension, and an intravenous form used in hospitals[1]. 

What is phenytoin used for?

Phenytoin is prescribed for the following conditions[1]: 

• Epilepsy – particularly tonic-clonic (grand mal) and focal seizures 

• Seizures following neurosurgery or severe head injury 

• Trigeminal neuralgia – a chronic facial pain condition 

How does phenytoin work?

Phenytoin works by stabilising electrical activity in the brain. It blocks sodium channels in nerve cells, helping to prevent the abnormal electrical impulses that can cause seizures[1]. 

Who can take phenytoin?

Phenytoin can be used by adults and children, but it is not suitable for everyone. You should speak to your doctor first if you[1]: 

• Are allergic to phenytoin or related drugs (e.g. hydantoins) 

• Have certain heart conditions such as bradycardia 

• Have liver disease, kidney problems, or a condition called porphyria 

• Cannot have alcohol as phenytoin liquid contains a small amount 

• Have ever had a rash caused by phenytoin 

• Are pregnant, trying to get pregnant, or are breastfeeding 

Please tell your doctor or pharmacist about any conditions you may have or medication you take before you start treatment, and always follow the instructions in the Patient Information Leaflet[2].  

What is the typical dosage of phenytoin?

Gormulations of phenytoin come in many strengths. Doses vary depending on your weight, age, condition, and how your body responds to the medicine. You may start on a lower dose which will gradually increase over time. It is important to take your phenytoin as prescribed by your clinician[1]. 

How do you take phenytoin? 

Phenytoin should be taken consistently and as prescribed. To take it correctly[1]: 

• Take with food to reduce stomach upset 

• Swallow capsules or tablets whole 

• Infatabs may be chewed if needed 

• Use the plastic spoon or syringe provided when taking the liquid and shake the bottle vigorously 

• If you are tube-fed, stop feed two hours before dosing and for two hours after. Phenytoin interacts with feed. Feeding tubes should be flushed before and after dosing with saline. 

How do you take phenytoin?

Phenytoin should be taken consistently and as prescribed. To take it correctly[1]: 

• Take with food to reduce stomach upset 

• Swallow capsules or tablets whole 

• Infatabs may be chewed if needed 

• Use the plastic spoon or syringe provided when taking the liquid and shake the bottle vigorously 

• If you are tube-fed, stop feed two hours before dosing and for two hours after. Phenytoin interacts with feed. Feeding tubes should be flushed before and after dosing with saline. 

Can you stop taking phenytoin?

No. Do not stop taking phenytoin suddenly, as this may cause seizures to return or worsen. Always consult your doctor or pharmacist before making any changes to your dose or treatment[1]. 

What do you do if you take too much phenytoin?

Taking too much can be dangerous. Symptoms of overdose may include[1]: 

• Loss of coordination 

• Slurred speech 

• Abnormal eye movements 

• Confusion or unconsciousness 

• Seek immediate medical help or call NHS 111 or 999 . 

What do you do if you forget to take phenytoin?

If you forget a dose[1]: 

• Take it as soon as you remember 

• If it’s nearly time for your next dose, skip the missed one 

• Do not take two doses at once 

How do you store phenytoin?

Storage depends on the form of medicine you’re using. For the liquid suspension, store at room temperature, ideally between 20-25°C. Capsules/tablets should be kept in the original packaging at room temperature in a dry place. Keep all medicine out of the reach of children and pets[1]. 

What medicines can’t you take with phenytoin?

Phenytoin interacts with many other medications. Some should be avoided, while others may require monitoring. Speak to your doctor first if you also take[1]: 

• Other epilepsy medication 

• HIV medication 

• HRT or hormonal contraception 

• Heart medication 

• Blood clot medication 

• Fungal infection medication 

• Tuberculosis medication 

• Medication for stomach problems 

• Sleeping medication 

• Cancer medication 

• Transplant mediation 

• St John’s wort 

Always inform your doctor or pharmacist about all medications and supplements you take before you start a new medicine, and follow the instructions in the Patient Information Leaflet[2]. 

What are the side effects of phenytoin?

Like all medicines, phenytoin can cause side effects. Common side effects include[1]: 

• Dizziness or drowsiness 

• Nausea or vomiting 

• Constipation 

• Sore gums or gum overgrowth (gingival hyperplasia) 

• Tremors or unsteadiness 

• Headaches 

Rare but serious side effects include[1]: 

• Skin rashes such as Stevens-Johnson syndrome 

• Liver problems 

• Blood disorders 

• Hypersensitivity reaction 

You should contact your GP if you experience any of these symptoms. In rare cases, the medicine may cause a serious allergic reaction (anaphylaxis). You should call 999 or visit A&E immediately if you believe this is happening[1]. 

Symptoms of anaphylaxis include[1]:  

• Difficulty breathing  

• Tightness in throat and chest  

• Swelling of the tongue or throat  

• Feeling faint or dizzy  

• Blue/grey skin or lips  

• Loss of consciousness 

If you experience any side effects, including those not listed, you are encouraged to report them via the Yellow Card Scheme or contact your doctor, pharmacist, or nurse. This information is intended as a summary for general awareness and does not replace professional medical advice. 

The information provided in the side effects section is not a comprehensive list of all possible side effects associated with this medication. For a complete list of side effects, please refer to the Patient Information Leaflet (PIL) provided with your medication or consult your healthcare professional[2]. 

Frequently asked questions about phenytoin

Can I drink alcohol with phenytoin? 
It’s best to avoid alcohol as it can interfere with phenytoin levels and reduce seizure control[1]. 

Can phenytoin affect pregnancy? 
Yes. Speak to your doctor about safer alternatives if you are pregnant or planning to become pregnant[1]. 

Can I switch brands of phenytoin? 
Only under medical supervision, as different brands may be absorbed differently by the body[1]. 

Does phenytoin cause gum problems? 
Yes. Good dental hygiene is important to prevent gum overgrowth[1]. 

How is phenytoin monitored? 
You’ll need regular blood tests to ensure levels stay within the safe and effective range[1]. 

Can phenytoin cause weight gain or loss? 
It may affect appetite in some people, but major weight changes are uncommon[1]. 

Is phenytoin safe for long-term use? 
Yes, with regular monitoring and follow-up from your doctor or pharmacist[1]. 

For the official NHS guide to phenytoin, visit their website.