Phenytoin

Phenytoin

Phenytoin, a widely used drug, has been a game-changer in treating epilepsy and other neurological disorders. This potent medication has an impact on the nervous system, helping to keep electrical activity in the brain in check and prevent seizures from happening.

In this article, we will explore what tablet phenytoin is, its uses, and how to take it safely. We will learn about the side effects of phenytoin tablets and essential precautions to keep in mind. 

What is Phenytoin?

Phenytoin is a powerful anticonvulsant drug that has been widely used for about 80 years. It belongs to the hydantoin derivative class and is primarily used to manage and treat various types of seizures without significantly affecting neurological function. The FDA approved phenytoin in 1939 for epilepsy treatment. 

Despite its narrow therapeutic index (the effective dose is close to the toxic dose), phenytoin remains a widely prescribed anticonvulsant. This is due to its effectiveness in controlling seizures without significantly affecting neurological function. It works in the brain tissue to stop seizures, making it a valuable tool in epilepsy management. Both oral and injectable forms of phenytoin are available, with the latter often used in emergencies.

Phenytoin Tablet Uses

Phenytoin tablets have a significant impact on managing various types of seizures, including:

• Grand mal seizures, also known as generalised tonic-clonic seizures
• Complex partial seizures
• Status epilepticus

Besides epilepsy management, phenytoin tablets have other uses, such as: 

• Phenytoin helps prevent seizures during or after neurosurgery, ensuring patient safety during these delicate procedures. 
• Some doctors prescribe phenytoin for trigeminal neuralgia, a painful nerve condition and certain behaviour disorders. 
• In some cases, it helps control irregular heartbeats.

How to Use Phenytoin Tablets

• Individuals should take phenytoin tablets once or twice daily, with or without food. If you are on a twice-daily schedule, space your doses evenly. For example, take one in the morning and another in the evening. 
• Swallow the tablets whole with water, milk, or juice and do not chew them.
• It is important to take phenytoin precisely as prescribed. Do not take more or less than directed, and stick to the same daily schedule. Your doctor might start you on a low dose and gradually increase it, usually less often than once every 7 to 10 days.

Side Effects of Phenytoin Tablets

Phenytoin tablets can cause various side effects, ranging from mild to severe. Common phenytoin side effects include: 

• Headaches
• Dizziness
• Drowsiness 
• Swelling and bleeding of the gums
• Nervousness or shakiness 
• Some people report feeling or being sick, constipation, and trouble sleeping.

Serious side effects may include: 

• Unusual eye movements
• Loss of coordination
• Trouble speaking
• Confusion
• Muscle twitching
• Liver problems
• High blood sugar (hyperglycaemia)
• Severe allergic reactions, including skin rashes, swelling of the face, lips, tongue, or throat, and itching

Precautions

When taking phenytoin, you need to be aware of several essential precautions, such as: 

• Allergy History: Tell your doctor about your allergies, especially hydantoin products or other anti-seizure medications. 
• Pregnancy: If you are pregnant or planning to conceive, discuss the risks and benefits with your doctor, as phenytoin may harm an unborn baby. However, do not stop taking it without medical advice, as uncontrolled seizures can also be dangerous during pregnancy.
• Change of Alertness: Be cautious when driving or operating machinery, as phenytoin can cause drowsiness and affect coordination. 
• Alcohol: Avoid alcohol while using this medicine, as it can increase side effects. 
• Monitoring: Regular check-ups are essential to monitor your progress and adjust the dose if needed. Blood and urine tests may be necessary to check for unwanted effects.
• Systemic Conditions: If you have diabetes, liver disease, thyroid disease, or blood disorders or are receiving radiation therapy, inform your doctor, as these conditions may affect how phenytoin works in your body.

How Phenytoin Tablet Works

Phenytoin tablets block voltage-dependent sodium channels in the brain. This action stops the positive feedback loop that causes high-frequency repetitive firing of neurons, which is responsible for seizures. By doing this, phenytoin prevents the spread of seizure activity from its starting point.

As a voltage-gated sodium channel blocker, phenytoin stabilises the inactive state of these channels. This prolongs the refractory period between action potentials in neurons, making it harder for seizures to continue. Phenytoin mainly targets neurons with high-frequency activity, often involved in seizures.

The drug's effects are not limited to the brain. In cardiac tissue, phenytoin shortens action potentials and extends the refractory period between them. This dual action on neuronal and cardiac tissue makes phenytoin a versatile medication for managing various types of seizures and certain heart conditions.

Can I Take Phenytoin with Other Medicines?

Phenytoin can interact with other medicines, such as: 

• Abacavir
• Abatacept
• Acarbose
• Aceclofenac
• Antibiotics
• Antifungal drugs
• Aspirin
• Atorvastatin
• HIV medications 
• Antidepressants
• Blood thinners 
• Medications for blood pressure, heart disease, irregular heartbeat
• Female hormones, like birth control pills and oestrogen 
• Steroids like prednisone or cortisone
• St John's wort
• Theophylline
• Ticlopidine

Remember, phenytoin can also affect how well other medications work. Always check with your doctor or pharmacist before starting any new medicine while on phenytoin.

Dosing Information

When taking phenytoin, carefully following your doctor's instructions is mandatory. 

For adults with seizures, the typical starting dose is 100 mg taken orally three times a day. Your doctor may adjust this dose as needed, with most adults being maintained on 300 to 400 mg per day in divided doses. The maximum dose is usually 600 milligrams per day.

For children over six years old, the usual dose is 300 mg per day. Younger children's doses are based on body weight, starting at 5 mg per kilogram of a person's weight and are given as 2 or 3 divided doses daily.

Conclusion

Phenytoin has a significant impact on managing various types of seizures and certain heart conditions. This anti-seizure medication works by stabilising electrical activity in the brain, helping to prevent seizures without major effects on neurological function. Its versatility in treating different seizure types, from grand mal to complex partial seizures, makes it a valuable tool in epilepsy management. Despite its narrow therapeutic index, phenytoin remains widely prescribed due to its effectiveness.

When using phenytoin, following your doctor's instructions carefully & being aware of side effects & interactions is necessary. Regular health checks, including blood tests, may be necessary to monitor your progress and adjust the dose if needed. If you have any concerns or experience unusual symptoms, do not hesitate to contact your doctor for guidance.

FAQs

1. What is phenytoin drug used for?

Phenytoin is primarily used to control certain types of seizures in epilepsy. It is effective for managing grand mal seizures, complex partial seizures, and status epilepticus. Doctors also prescribe phenytoin to prevent seizures during or after brain surgery. In some cases, doctors may use it to treat trigeminal neuralgia, a type of facial nerve pain, and to control irregular heartbeats.

2. Is phenytoin a painkiller?

While phenytoin is not primarily a painkiller, it can help relieve certain types of nerve pain. It is sometimes used to treat trigeminal neuralgia by slowing down electrical impulses in the nerves, which reduces their ability to transmit pain signals. However, its primary use is as an anticonvulsant for seizure control.

3. When to take phenytoin?

You will typically take phenytoin once or twice a day, as your doctor prescribes. Individuals can take it with or without food, but it is essential to be consistent in how you take it. If you are on a twice-daily schedule, try to space your doses evenly, for example, in the morning and evening. It is important to follow your doctor's instructions carefully.

4. Why is phenytoin given at night?

Phenytoin is often given at night to ensure sufficient drug concentration in the blood & tissues by morning. It helps reduce the risk of morning epileptic seizures. Taking it at night may also help manage side effects like drowsiness or dizziness that some people experience when starting the medication.

5. What should I avoid with phenytoin?

Several medications can interact with phenytoin. Avoid taking it with certain antifungals, antibiotics, and HIV medications. Some antidepressants and blood thinners may also cause problems. Herbal products like St. John's wort can decrease phenytoin's effectiveness. Always inform your doctor about all your medicines and supplements to avoid potential interactions.

6. What foods should be avoided with phenytoin?

While there are no specific foods to avoid, it is essential to be consistent with your diet when taking phenytoin. Enteral feeding products can affect phenytoin absorption, so it is best to separate them by at least an hour before and after your dose. Individuals should avoid alcohol as it can affect phenytoin levels in your blood. Always consult your doctor about any dietary concerns.

7. What happens if I miss a dose?

If you miss a dose of phenytoin, take it as soon as you remember. However, if it is close to your next scheduled dose, skip the missed one and continue your regular dosage routine. Never take a double dose to make up for a forgotten one. If you are unsure, consult your doctor for guidance.