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Generally known as 'Dilantin' Phenytoin is a recommended treatment for a wide variety of Seizures. It is known for the prevention of partial and tonic-clonic seizures. It is also used as a muscle relaxant and an anti-arrhythmic agent. It is also known as Diphenylhydantoin, Phentytoin, Phentytoine, Phenytoin, Fenitoina, 5,5-Diphenyl-imidazolidine-2,4-dione among many other names.
Phenytoin is a drug under various classes of drugs due to its diverse use. It is used as an anticonvulsant, Anti-epileptic, Class 1b anti-arrhythmic drug and lastly muscle relaxants.
Mode of action
The mode of action of phenytoin is subdivided according to how it works on the body. It inhibits seizures by delaying impulses or curbing the flow of impulses that cause seizures. It does this by blocking voltage-dependent sodium channels which concurrently reduces the repetitive high-frequency ignition of action potentials. As a muscle relaxant, it reduces the sensitivity of muscle fibers to stretch. As an anti-arrhythmic agent, it blocks the sodium channel and prevents ventricular tachycardia and also the risk of myocardial infarction.
When treating or preventing convulsions, 100 milligrams taken orally, three times a day can help stop impulses that cause seizures. It is usually given as a phenytoin capsule but when a patient presents with status epilepticus, the Intravenous form of phenytoin is recommended ( especially when the common benzodiazepines have failed). When administered intravenously, phenytoin effects begin manifesting within 30 minutes. This drug is considered efficient within 24 hours.
The pharmacokinetics of phenytoin includes: Its bioavailability is 70% - 100% when administered orally and 24.5% when administered through the rectal route. It binds to albumin in blood at 95%. It is metabolized in the liver. Its elimination half-life is 10 - 20 hours. Its main routes of excretion are through the urine and bile. Phenytoin is also an enzyme inducer of the CYP enzymes which leads to fast degradation of certain drugs such as antacids.
Phenytoin may have various side effects which may be classified into two groups acute or chronic side effects. Acute or short-term side effects may appear 1 or 2 weeks after you start the medication while chronic effects may take months before they appear. Some side effects are common with phenytoin therapy while some are rare and may be different in individuals.
Common side effects
- Gastrointestinal effects- Nausea, Vomiting, Diarrhea or Constipation.
- Sedation and confusion however this is mitigated by taking the drug at night.
- Loss of muscle co-ordination
- Skin rash.
- Yellow eyes or skin which may be a sign of jaundice
- Poor appetite
- Visual problems example blurred vision and double vision
- Change in sleep patterns or even insomnia
Chronic side effects
These side effects may occur with prolonged use (over a number of months) of the drug. They include:
- Hypertrophy of the gums and bleeding gums.
- Peripheral neuropathy leading to a feeling of pins and needles in the extremities or numbness.
- Megaloblastic anemia as it causes folate deficiency.
- Hirsuitism - Excess growth of hair in the human body due to hyperactivation of androgenic hormones
It is important you consult your doctor or pharmacist in case you start to encounter any of the following side effects as he or she will advise you accordingly.
Phenytoin Sodium may interact with some drugs which may affect the overall potency of the drug. When two or more drugs are administered concurrently one may antagonize or potentiate the effects of another drug leading to undesirable effects. It is therefore important to inform your doctor or pharmacist of any drug you may be taking so as to avoid any possible drug interactions.
Warning / caution
Phenytoin as other drugs is a medication that should be kept out of children's' reach. You should also inform the doctor of your medical history or any underlying medical condition such as
- Liver diseases.
- Kidney disease.
- Any heart conditions.
- Any Vitamin deficiencies example Folate or Vitamin B12.
If you take alcohol - It has been proven that if you take more than 30 units of alcohol per day will reduce the levels of plasma phenytoin by approximately 1/3 which will lead to low bio-availability.
Any allergies you might be having either to medications or ingredients.
Asians have an increased risk of severe skin reactions when taking phenytoin. In this case, the doctor orders a blood test before they prescribe the medication so as to ascertain the risk.
Phenytoin is classified under Category D in pregnancy drugs hence it is harmful to the unborn baby. It is a teratogenic drug. Use of phenytoin in pregnancy causes Fetal Hydantoin Syndrome which is associated with a Congenital heart condition, slow growth and cleft lip.
Phenytoin sodium should also be avoided in nursing mothers as it is found in breast milk.
Do not start or stop the medication without consulting your doctor.
Phenytoin price is not that costly as compared to most drugs. It is the cheapest anti-seizure drug available. You can buy phenytoin online on various sites which are accredited to sell drugs through their websites such as FairPriceRX.com