Phenytoin

Brand names

• Dilantin
• Dilantin Infatabs
• Di-Phen
• Diphenylan
• Ekko JR
• Ekko SR
• Ekko Three
• Mebroin [CD]
• Novo-Phenytoin
• Phelantin

Usage

To prevent or control seizures in the treatment of certain types of epilepsy and other conditions.

How it works

Phenytoin is thought to depress the activity of certain parts of the brain and suppress the irregular and uncontrolled firing of neurons that causes seizures.

Side effects

Serious

Fever, sore throat, swollen glands, point like rash on the skin or mucous membranes, blistering or peeling, mouth sores or bleeding gums, easy bruising, pallor, weakness, confusion, or seizures may be a sign of a potentially fatal blood disorder or other complication. Seek medical help immediately.

Common

Sedation, lethargy, nervousness, dizziness, thickened gums, excessive growth of body and facial hair. High doses may cause abnormal movements of the eyes, mouth, tongue, or limbs. Prolonged use may cause mild nerve impairment in the arms or legs.

Less common

Constipation, acne, mild skin rash, incoordination. There are numerous additional possible side effects; consult your doctor if you are concerned about any adverse or unusual reactions.

Possible interactions

Other medicaments:

Phenytoin may decrease the effects of:

• acetaminophen (Tylenol, others).
• acyclovir (Zovirax).
• bupropion (Wellbutrin).
• clofibrate (Atromid-S).
• conjugated estrogens (Premarin).
• cortisonelike medicaments.
• cyclosporine (Sandimmune).
• disopyramide (Norpace).
• doxycycline (Vibramycin,etc.).
• itraconazole (Sporanox).
• levodopa (Larodopa, Sinemet).
• levothyroxine (Synthroid, others).
• meperidine (Demerol).
• methadone (Dolophine).
• mexiletine (Mexitil).
• miconazole (Monistat, Micatin, others).
• oral antidiabetic medicaments.
• oral contraceptives (birth control pills).
• paclitaxel (Taxol).
• paroxetine (Paxil).
• quetiapine (Seroquel).
• quinidine (Quinaglute, etc.).
• ritonavir (Norvir) and perhaps other protease inhibitors.
• triamcinolone.

Phenytoin taken concurrently with:



• acetazolamide (Diamox) may lead to bone problems (osteomalacia).
• carbamazepine (Tegretol) may result in increased or decreased levels of phenytoin.
• chlordiazepoxide (Librium, and perhaps other benzodiazepines) may increase or decrease phenytoin levels; levels should be obtained more frequently if these medicaments are combined.
• ciprofloxacin (Cipro) may increase or decrease phenytoin levels.
• dopamine will result in very low blood pressure.
• flu shots (influenza vaccine) may change phenytoin levels.
• ketorolac (Toradol) may result in seizures.
• oral anticoagulants (Coumadin, etc.) can either increase or decrease the anticoagulant effect; monitor this combination very closely with INR (serial prothrombin) testing.
• primidone (Mysoline) may alter primidone actions and enhance its toxicity.
• theophyllines (Aminophyllin, Theo-Dur, etc.) may cause a decrease in the effectiveness of both medicaments.
• valproic acid (Depakene) may result in altered phenytoin or valproic acid levels; increased blood level testing of both medicines is needed if these medicines are to be combined.
• warfarin (Coumadin) may lead to initial increased bleeding risk and subsequent decrease in anticoagulation; more frequent INR (prothrombin time or protime) testing is needed. Warfarin doses should be adjusted to results.

The following medicaments may increase the effects of phenytoin:



• amiodarone (Cordarone).
• chloramphenicol (Chloromycetin).
• chlorpheniramine.
• cimetidine (Tagamet).
• clopidogrel (Plavix).
• cotrimoxazole (Bactrim).
• diltiazem (Cardizem).
• disulfiram (Antabuse).
• felbamate (Felbatol).
• fluconazole (Diflucan).
• fluoxetine (Prozac).
• fluvoxamine (Luvox).
• gabapentin (Neurontin).
• ibuprofen and perhaps other NSAIDs.
• isoniazid (INH, Niconyl, etc.).
• nefazodone (Serzone).
• nifedipine (Adalat).
• omeprazole (Prilosec).
• phenacemide (Phenurone).
• S-Liposomal doxorubicin.
• sertraline (Zoloft).
• sulfonamides.
• trazodone (Desyrel).
• tricyclic antidepressants.
• trimethoprim (Proloprim, Trimpex).
• valproic acid (Depakene).
• venlafaxine (Effexor).
• zotepine (Nipolept).

The following medicaments may decrease the effects of phenytoin:



• bleomycin (Blenoxane).
• carmustine (BiCNU).
• cisplatin (Platinol).
• diazoxide (ProgIycem, Hyperstat).
• folic acid (various).
• methotrexate (Mexate).
• rifampin (Rifadin).
• vinblastine (Velban).

Herbal medicines or minerals:

Using kola or ma huang may result in unacceptable central nervous system stimulation. Valerian and kava kava may interact to increase drowsiness. St. John's wort may also cause increased sun sensitivity-caution is advised. Increased calcium and vitamin D are prudent.
Supplements of folic acid, calcium, vitamin D and vitamin K may be necessary.

Alcohol:

Alcohol (in large quantities or with continual use) may reduce this medicament's effectiveness in preventing seizures.

Exposure to sun:

Use caution-this medicament may cause photosensitivity.

Occurrence of unrelated illness:

Intercurrent infections may slow the elimination of this medicament and increase the risk of toxicity, due to higher blood levels.

Discontinuation:

This medicament must not be discontinued abruptly. Sudden withdrawal can precipitate severe and repeated seizures. If this medicament is to be discontinued, gradual reduction in dose should be made over a period of 3 months. Total medicament withdrawal may be attempted after a period of 3 to 4 years without a seizure. However, seizures are likely to recur in 40% of adults and in 20-30% of children.