Phenytoin

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Chemical structure of Phenytoin.

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Phenytoin 3D balls

Phenytoin

Phenytoin, historically known as diphenylhydantoin, is a prominent anticonvulsant medication, with its primary application in the management and prevention of epileptic seizures. It is widely recognized under the brand name Dilantin™. Introduced in the mid-20th century, this hydantoin derivative has become a cornerstone in antiepileptic therapy.

Introduction

Phenytoin is amongst the most frequently prescribed major anticonvulsant agents, having demonstrated significant efficacy in controlling seizures and offering a relatively safe profile when used appropriately.

Mechanism of Action

The therapeutic potential of phenytoin primarily emanates from its ability to stabilize neuronal membranes. The medication achieves this by promoting the efflux and limiting the influx of sodium ions across GABA-regulated sodium channels. This ion channel modulation curtails excessive neuronal firing, often implicated in seizure activity. Apart from its neuroprotective action, phenytoin exerts a similar effect on cardiac muscle, explaining its efficacy against certain ventricular arrhythmias.

FDA Approval and Usage Trends

The FDA first sanctioned the use of phenytoin in the United States in 1946. Since its introduction, the drug's utility has only soared, with more than 3 million prescriptions currently being dispensed annually.

Clinical Indications

Phenytoin's primary indications encompass:

• Prevention and treatment of generalized tonic-clonic (grand mal) seizures.
• Management of complex partial seizures.
• Addressing status epilepticus, a life-threatening condition characterized by prolonged seizures or rapid seizure succession without regaining consciousness in between.
• Historically, phenytoin was employed to curtail ventricular arrhythmias, especially in patients non-responsive to lidocaine. This use has become less prevalent in recent times.

Formulations and Dosage

Phenytoin is procurable in both generic and brand-name formats in a myriad of oral and parenteral formulations.

Dosage Forms

• Oral: Tablets and capsules ranging from 100 to 300 mg, inclusive of extended-release variants suitable for once-daily administration.
• Parenteral: Injectable solutions for intravenous or intramuscular use.

Commercial Names: Apart from the renowned Dilantin, phenytoin is available under various other trade names. Special formulations, such as chewable tablets and oral suspensions, cater to pediatric populations.

Recommended Administration

The endorsed phenytoin dosage for chronic therapy is 100 mg administered thrice daily. However, the precise dose may be tailored according to the patient's age, condition, and associated therapy.

Side Effects and Drug Interactions

Like any medication, phenytoin use is not devoid of side effects. Commonly observed adverse reactions include:

• Dizziness
• Ataxia (lack of muscle control)
• Nausea
• Gum hyperplasia (overgrowth)
• Rashes, observed in around 10% of patients.

Furthermore, phenytoin exerts a profound influence on the metabolism of various other medications. This interaction potential necessitates caution, and patients should receive comprehensive advice regarding concomitant drug usage during prolonged phenytoin therapy.

Liver Safety

Although rare, phenytoin is a recognized causative agent of acute idiosyncratic drug-induced liver disease. The ensuing liver pathology, in grave instances, can prove fatal. Monitoring liver function and being vigilant for signs of liver compromise is essential during therapy.

See Also

• Anticonvulsant
• Epilepsy
• Liver disease
• Drug interactions
• GABA

• Dailymed label info on Phenytoin
• FDA Phenytoin