M-TOIN 100

# Phenytoin 100 mg ## Short Description **Phenytoin 100 mg** is an **antiepileptic (anticonvulsant) medicine** used to control and prevent certain types of seizures. It works mainly by stabilizing electrical activity in the brain and reducing the rapid, repetitive firing of nerve cells. Phenytoin has a **narrow therapeutic range**, meaning the difference between an effective dose and a potentially toxic dose can be relatively small. Blood-level monitoring may therefore be required for some patients. --- ## Key Benefits * Helps **control and prevent certain seizures**. * Reduces abnormal electrical activity in the brain. * Commonly used for **focal (partial) seizures** and **generalized tonic-clonic seizures**. * May be used alone or together with other antiseizure medicines. * Can help reduce seizure frequency when appropriately prescribed. * Available in a convenient **100 mg strength** for individualized dosing. --- ## Uses / Indications Phenytoin may be prescribed for: ### 1. Focal (Partial) Seizures It can be used for seizures that originate in a specific area of the brain. ### 2. Generalized Tonic-Clonic Seizures Phenytoin may help control generalized tonic-clonic seizures. ### 3. Seizure Prevention After Certain Brain Injuries In selected circumstances, phenytoin may be used for seizure prevention following neurosurgical procedures or significant brain injury, according to specialist judgment. ### Important Phenytoin is **not generally effective for absence seizures** and may worsen certain seizure types. The exact choice of antiseizure medicine should be based on the patient's seizure type and medical history. --- ## How It Works Phenytoin primarily acts by blocking **voltage-dependent sodium channels** in nerve cells. This limits the ability of neurons to produce rapid, repetitive electrical signals. ### Simple Mechanism **Phenytoin → blocks sodium channels → reduces repetitive nerve firing → stabilizes brain electrical activity → helps prevent seizures.** Phenytoin does not cure epilepsy, but regular treatment can help control seizures. --- ## Dosage & Administration > **Phenytoin dosage must be individualized by a healthcare professional.** Do not change the dose without medical advice. ### Adults A commonly used maintenance dose is approximately **300–400 mg per day**, divided or given according to the specific formulation and prescribing instructions. For some patients, lower or higher doses may be required based on: * Seizure control * Age * Body weight * Liver function * Other medicines * Blood phenytoin concentration * Individual response **Phenytoin 100 mg tablets/capsules may therefore be used as one part of an individualized daily regimen.** ### Children Dosing is generally based on **body weight** and must be determined by a healthcare professional. ### Administration * Take exactly as prescribed. * Take doses at the same time each day. * Swallow tablets/capsules with water. * Do not stop treatment suddenly. * Do not change between different phenytoin formulations or brands without medical advice because absorption and blood levels can differ. ### Blood-Level Monitoring Because phenytoin has a narrow therapeutic range, your doctor may order **blood tests** to monitor phenytoin concentrations, particularly after dose changes or when seizure control or adverse effects change. ### Missed Dose Take the missed dose when remembered unless it is nearly time for the next dose. **Do not take two doses together** to compensate for a missed dose. --- ## Side Effects ### Common Side Effects Possible side effects include: * Dizziness * Drowsiness * Headache * Nausea * Vomiting * Unsteadiness * Blurred or double vision * Difficulty with coordination * Slurred speech Some side effects may become more likely when blood phenytoin levels are too high. ### Gum Changes Long-term treatment can cause: * **Gum enlargement** * Tender or swollen gums * Increased risk of gum disease Good oral hygiene and regular dental care are particularly important. ### Serious Side Effects Seek immediate medical attention for: * Severe skin rash * Blistering or peeling skin * Mouth or eye sores * Facial swelling * Difficulty breathing * Unusual bruising or bleeding * Persistent fever or sore throat * Yellowing of the skin or eyes * Severe confusion * Loss of coordination * Severe dizziness or difficulty walking Rare but serious reactions include **Stevens-Johnson syndrome/toxic epidermal necrolysis, DRESS syndrome, liver injury and serious blood disorders**. --- ## Precautions & Warnings ### Do Not Stop Suddenly Abruptly stopping phenytoin can cause **breakthrough seizures or prolonged seizures**. ### Narrow Therapeutic Range Small changes in blood concentration can sometimes produce significant changes in effectiveness or side effects. Follow the prescribed dose carefully. ### Liver Disease Phenytoin is extensively metabolized by the liver. Patients with liver disease may require dose adjustment and closer monitoring. ### Kidney Disease or Low Albumin Phenytoin is highly protein-bound. Changes in albumin levels or kidney function can alter the amount of active drug in the blood. ### Skin Reactions Stop and seek urgent medical advice if a rash develops, particularly if accompanied by: * Fever * Facial swelling * Blistering * Peeling skin * Mouth ulcers * Eye irritation ### Genetic Risk Certain genetic variants, particularly **HLA-B*15:02**, are associated with an increased risk of severe cutaneous reactions to phenytoin in susceptible populations. Genetic testing may be considered for people from populations where this variant is more common. ### Pregnancy Phenytoin can cause fetal harm and is associated with an increased risk of congenital abnormalities and other pregnancy-related complications. However, **uncontrolled seizures during pregnancy can also be dangerous**. Patients who are pregnant or planning pregnancy should discuss treatment with a specialist and should not stop phenytoin abruptly. ### Vitamin D and Bone Health Long-term phenytoin therapy may affect vitamin D metabolism and contribute to reduced bone mineral density. Your healthcare professional may recommend monitoring and appropriate nutritional or bone-health measures. ### Oral Health Maintain good dental hygiene and attend regular dental check-ups because phenytoin can cause gum enlargement. ### Driving and Machinery Phenytoin may cause dizziness, drowsiness or impaired coordination. Avoid driving or operating machinery until you know how the medicine affects you and according to local driving regulations. --- ## Drug Interactions Phenytoin has **many clinically important drug interactions**. ### Medicines That May Increase Phenytoin Levels Examples include certain: * Antibiotics * Antifungal medicines * Acid-suppressing medicines * Antidepressants * Other medicines that inhibit phenytoin metabolism Increased levels can cause toxicity. ### Medicines That May Decrease Phenytoin Levels Some medicines can increase phenytoin metabolism and reduce seizure control, including certain: * Antiseizure medicines * Antituberculosis medicines * Herbal products ### Oral Contraceptives Phenytoin can increase the metabolism of **hormonal contraceptives**, potentially reducing their effectiveness. Discuss reliable contraception options with your healthcare professional. ### Warfarin and Other Medicines Phenytoin can interact with **warfarin** and other medicines that have a narrow therapeutic range. Blood tests may be required. ### Valproate Phenytoin and valproate can affect each other's blood concentrations and protein binding. Monitoring may be necessary. ### Antacids and Calcium Products Some antacids and calcium-containing products may reduce phenytoin absorption. Follow your pharmacist's instructions regarding spacing these products from phenytoin. ### Enteral Tube Feeding Liquid nutritional feeds can interfere with phenytoin absorption. Patients receiving tube feeding may require specialized administration and monitoring instructions. ### Alcohol Alcohol can affect phenytoin levels and central nervous system effects. Discuss alcohol consumption with your healthcare professional. > Always provide your doctor or pharmacist with a complete list of prescription medicines, OTC medicines, vitamins and herbal supplements. --- ## Storage Information * Store at **room temperature**, according to the manufacturer's instructions. * Keep away from excessive heat and moisture. * Keep the medicine in its original packaging. * Keep the container tightly closed. * Protect from direct sunlight. * Keep out of reach of children. * Do not use after the expiry date. * Do not use tablets/capsules if the packaging is damaged or the medicine appears abnormal. --- ## Prescription Status **Phenytoin 100 mg is a prescription medicine.** It requires medical supervision because of its narrow therapeutic range, numerous drug interactions and potentially serious adverse effects. --- ## Genuine Medicine Assurance When purchasing **Phenytoin 100 mg**: * Purchase only from a **licensed and reputable pharmacy**. * Verify the active ingredient and **100 mg strength**. * Check the manufacturer's name and regulatory information. * Check the batch/lot number and expiry date. * Ensure the packaging is sealed and undamaged. * Confirm that the dosage form matches the prescription. * Avoid medicines with suspicious packaging, altered labels or unclear manufacturing information. * Do not substitute one phenytoin formulation or brand for another without professional advice. * If counterfeit medicine is suspected, contact the manufacturer, licensed pharmacy or relevant medicines regulatory authority. --- # Frequently Asked Questions (FAQ) ### 1. What is Phenytoin 100 mg used for? Phenytoin 100 mg is an **antiepileptic medicine** used to control certain seizures, particularly focal seizures and generalized tonic-clonic seizures. ### 2. Is Phenytoin a seizure medicine? Yes. Phenytoin is an anticonvulsant that helps prevent abnormal electrical activity in the brain. ### 3. How does Phenytoin work? It mainly blocks voltage-dependent sodium channels, reducing rapid and repetitive electrical firing of nerve cells. ### 4. Is Phenytoin 100 mg a high dose? The 100 mg strength is a commonly available dosage strength, but whether a patient's total daily dose is appropriate depends on individual factors. **Do not determine your dose based on tablet strength alone.** ### 5. Can I stop taking Phenytoin suddenly? **No.** Abrupt discontinuation can cause breakthrough seizures or potentially prolonged seizures. Stopping should be done only under medical supervision. ### 6. Does Phenytoin need blood tests? Blood-level monitoring may be recommended because phenytoin has a **narrow therapeutic range** and many factors can affect its concentration. ### 7. What are the common side effects of Phenytoin? Common effects include dizziness, drowsiness, unsteadiness, blurred or double vision, nausea and coordination problems. ### 8. Can Phenytoin cause gum swelling? Yes. **Gingival enlargement** is a recognized effect of long-term phenytoin treatment. Good oral hygiene and regular dental care can help reduce the risk. ### 9. Can Phenytoin cause dizziness? Yes. Dizziness, drowsiness and problems with coordination can occur, particularly when treatment is started or blood levels are high. ### 10. Can Phenytoin cause a skin rash? Yes. Mild rashes can occur, but serious skin reactions are also possible. Seek urgent medical attention for rash accompanied by fever, facial swelling, blistering or peeling. ### 11. Does Phenytoin interact with other medicines? Yes. Phenytoin has **many drug interactions**, including interactions with hormonal contraceptives, anticoagulants, antibiotics, antifungals and other antiseizure medicines. ### 12. Does Phenytoin reduce the effectiveness of birth control? Yes. Phenytoin can increase the metabolism of some **hormonal contraceptives**, potentially reducing their effectiveness. Discuss contraception with your healthcare professional. ### 13. Can Phenytoin be taken during pregnancy? Phenytoin can affect fetal development, but uncontrolled seizures can also pose serious risks. Patients who are pregnant or planning pregnancy should consult their specialist and **must not stop phenytoin suddenly**. ### 14. Can Phenytoin affect bones? Long-term treatment may contribute to reduced bone mineral density and vitamin D-related problems. Your healthcare professional can advise on appropriate monitoring and bone health. ### 15. Can I take antacids with Phenytoin? Some antacids and calcium-containing products can reduce phenytoin absorption. Ask your pharmacist about appropriate timing and spacing. ### 16. What should I do if I miss a Phenytoin dose? Take it when remembered unless it is nearly time for the next dose. **Do not double the next dose.** If multiple doses are missed, contact your healthcare professional. ### 17. Can I drink alcohol while taking Phenytoin? Alcohol can affect phenytoin levels and increase dizziness or other nervous-system effects. Discuss alcohol use with your healthcare professional. ### 18. Does Phenytoin cure epilepsy? Phenytoin generally **controls seizures rather than curing the underlying cause of epilepsy**. Some people may require long-term treatment. ### 19. Can Phenytoin cause blurred or double vision? Yes. Blurred or double vision can occur, particularly when phenytoin blood levels are elevated. ### 20. Is Phenytoin 100 mg available without a prescription? Phenytoin is generally a **prescription-only medicine** because it requires careful dosing and monitoring. --- ## Medical Disclaimer This information about **Phenytoin 100 mg** is provided for educational and general informational purposes only. It is **not a substitute for professional medical advice, diagnosis or treatment**. Phenytoin has a narrow therapeutic range and numerous drug interactions. Serious adverse reactions, including severe skin reactions, liver injury and blood disorders, can occur. Treatment and blood-level monitoring should be individualized by a qualified healthcare professional. **Do not start, stop, or change the dose of Phenytoin without medical supervision.** Patients who are pregnant, planning pregnancy, or taking multiple medicines should discuss treatment with their healthcare professional. Always follow the **specific product label and your healthcare professional's prescribed treatment plan**.