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Cerebyx (fosphenytoin sodium) is an injected drug used to control seizures. It is only for short term use, 5 days maximum, and used when oral medications are not available, inappropriate or not effective. It is often used during brain surgery. Cerebyx turns into the antiepileptic drug phenytoin when metabolized.

Cerebyx is only available by prescription, and is most likely to be used by physicians during a hospital stay.

Cerebyx Side Effects

Common Side Effects:Confusion, constipation, discolored urine, dizziness, drowsiness, fatigue, headache, involuntary eye movements, loss of coordination, numbness, itching or tingling skin, slurred speech.

Infrequent Side Effects: Bleeding or tender gums, calcium deficiency, clumsiness, coarsened facial features, elevated blood sugar, enlarged gums due to excessive tissue growth (most often in children), enlarged lips, excessive body hair (most often in young girls), fever, involuntary eye movements (back and forth, or rolling), irritability, nausea or vomiting, nervousness, painful muscles, sore throat, swollen glands, trembling, unsteadiness, unusual excitement. Speak to your doctor as soon as possible if any of these effects occur. Seek medical attention if they seem severe.

Rare and Serious Side Effects: Agitation, anemia, bone marrow depression, chest discomfort, difficulty learning (children), dizziness, fever and chills, frequent bone fractures or breaks, headache, joint pain, light gray stools, low thyroid function, malformed bones, numbness or tingling in extremities (long-term use), painful erection, restlessness, severe stomach pain, severe skin reaction (bleeding, crusting, dark spots), shallow or troubled breathing, uncontrolled jerking of limbs, uncontrolled facial movements, unusual bleeding or bruising, weight loss, yellow eyes or skin. Seek medical attention if you experience any of these effects.

Overdose: Blurry or double vision, clumsiness, confusion, dizziness, drowsiness, seizure, slurred speech, staggering, stuttering, unsteadiness. If any of these symptoms are severe, and particularly if several appear together, seek medical attention immediately.

An overdose of this medication is potentially lethal. If you or a family member takes this medication, watch carefully for the signs of overdose. Immediate attention is required if you suspect that either accidentally or by intent a greater than normal dose has been taken.

Some overdose symptoms appearing mildly and in isolation may indicate that the regular dose is too high, but should be reported to your doctor or medical personnel anyway. They will need to make the determination regarding any need for care or dosage adjustment.

Cautions: Cerebyx may not be a suitable medication for everyone. To ensure that your treatment is safe and effective, discuss any of the following conditions, or any history of them with your doctor.

• Allergy: If you have an allergic reaction to Cerebyx, or have had one in the past, you will not be able to continue to use it. Also inform your doctor if you've had any other medication allergies, especially other antiseizure medication or barbiturates.
• Blood Disease: Rare but potential risk of serious infection.
• Diabetes: This condition may be worsened, this medication may raise blood sugar.
• Heart block or Sinus Bradycardia: Do not use.
• High Fever (sustained): A temperature that stays over 101 degrees for more than 24 hours may decrease the effectiveness of treatment.
• Kidney Disease: Cerebyx may build up in the system with an increased risk of side effects. Your dosage and blood levels should be carefully monitored, this medication may not be right for you.
• Liver Disease or Impairment: Speak to your doctor. You may require a dosage adjustment, as your body may not be able to clear Cerebyx out of the system as easily. If you have a very severe condition, this medication may not be right for you.
• Lupus: Cerebyx may make this condition worse.
• Other Drugs: Talk to your doctor about any medications, prescription or over the counter, that you currently use or may use in the future. Inform any other doctor besides your prescribing physician, as well as your pharmacist, that you are taking this medication.
• Porphyria: Cerebyx is not a safe medication for porphyria, and may make the condition worse.
• Surgery: If you plan to have surgery or dental work under anesthesia, inform your doctor that you use this medication.
• Thyroid Disease: Cerebyx may cause the drugs that treat this condition to be less effective.

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This medication should not be mixed with all prescription or over the counter drugs. Let your doctor know of any medications you're taking, or plan to take. Be especially careful with medications that may cause you to become drowsy or can alter seizure patterns.

• Acetaminophen (Tylenol, etc.) may be less effective when used with phenytoin.
• Adalat (nifedipine) - May increase the effects of phenytoin.
• Alcohol - Phenytoin may be less effective at reducing seizures when combined with large quantities of alcohol. Speak to your doctor for safe use guidelines, and keep your use minimal and infrequent.
• Antabuse (disulfiram) - May increase phenytoin effects.
• Antacids - Do not use within 2 hours of your phenytoin dose, may make treatment less effective.
• Antidiabetic drugs - Any oral antidiabetic medications may be less effective when used with Cerebyx, check your blood sugar regularly.
• Aricept (donepezil) - May be less effective when used with phenytoin.
• Atromid-S (clofibrate) - May be less effective when used with phenytoin.
• Azole antifungals like Bactrim (cotrimoxazole), Diflucan (fluconazole), Flagyl (metronidazole), Monistat (miconazole), Nizoral (ketoconazole), Sporanox (itraconazole), etc. may be less effective when used with phenytoin, or may increase its effects. Speak with your doctor about the possible need for dosage adjustments.
• Benzodiazepines (a class of antidepressants, anti-panic agents, sleep medications, and muscle relaxants) such as Valium (diazepam), Halcion (triazolam), Restoril (temazepam), Librium (chlordiazepoxide), Tranxene-SD (clorazepate), Klonopin (clonazepam), Paxipam (halazepam), Ativan (lorazepam), ProSom (estazolam), or Xanax (alprazolam) can result in altered blood levels of phenytoin. Your blood levels may need to be checked more often if the treatments are combined.
• BiCNU (carmustine) - Phenytoin may be less effective.
• Blenoxane (bleomycin) - Phenytoin may be less effective.
• Bronchodilators of the xanthine (thioxanthine) class (Aminophylline, Dyphylline, Oxtriphylline, Somophyllin, Theo-Dur, etc...) - Both medications may be less effective.
• Calcium - Absorption of this essential mineral may be interfered with. Speak with your doctor about getting enough through diet and/or supplementation. Calcium supplements should not be taken at the same time as phenytoin. Persistent calcium deficiency may lead to osteoporosis.
• Cardizem (diltiazem) - May increase phenytoin levels.
• Chloromycetin (chloramphenicol) - May increase phenytoin levels.
• Chlorpheniramine - May increase phenytoin levels.
• Cipro (ciprofloxacin) - May alter phenytoin levels either direction. Your doctor will have to check blood levels more frequently.
• Clozaril (clozapine) - May be less effective when used with phenytoin.
• Contraceptive injections/implants (progestin) - Risk of contraceptive failure and breakthrough bleeding.
• Cordarone (amiodarone) - May increase effects of phenytoin.
• Cortisone and related drugs can be less effective.
• Coumadin (warfarin) - May either increase or decrease anticoagulant effect. Your doctor will need to adjust your dosage accordingly.
• Crystodigin (digitoxin) - This combination may alter the effects of these medications.
• Demerol (meperidine) - May be less effective when used with phenytoin.
• Depakene (valproic acid) - These medications may alter each others blood levels unpredictably. More frequent testing will be necessary in order to use these treatments together.
• Desyrel (trazodone) - May increase the effects of phenytoin.
• Diamox (acetasolamide) - Bone problems such as osteomalacia may result.
• Dolophine (methadone) - May be less effective when used with phenytoin.
• Dopamine - Very low blood pressure may result. First indications are light-headedness, dizziness (esp. when standing up), and fatigue.
• Effexor (venlafaxine) - May increase phenytoin levels.
• Felbatrol (felbamate) - May increase phenytoin effects.
• Flu shots (influenza vaccination) - Can alter phenytoin levels, have your blood levels checked if you need to get vaccinated.
• Folic acid - May cause phenytoin to be less effective. Talk to your doctor for nutritional supplement guidelines, and how far doses should be separated. You may become deficient in this critical nutrient if a supplement plan is not set up.
• HMG-CoA reductase inhibitors (statins) - Drugs like Lescol (fluvastatin), Lipitor (atorvastatin), Mevacor (lovastatin), Pravachol (pravastatin), or Zocor (simvastatin) may be less effective when used with phenytoin. Your doctor may want to check your cholesterol more frequently.
• INH (isoniazid) - Phenytoin may build up in the body, have your doctor check your blood levels.
• Lanoxin (digoxin) - Lanoxin's effects may be increased.
• Lasix (furosemide) - This combination may alter the effects of these medications.
• Lidocaine - Possible risk of slow heartbeat and less effective anesthesia.
• Mexate (methotrexate) - Phenytoin may be less effective.
• Mexitil (mexiletine) - May be less effective when used with phenytoin.
• Moban (molindone) - This combination may alter the effects of these medications.
• Mysoline (primidone) - This medication's effects may be altered and its toxicity increased when used with phenytoin.
• Neuromuscular blocking agents like Norcuron (vecuronium) or Pavulon (pancuronium) may be less effective when used with this medication.
• Neurontin (gabapentin) - Can increase phenytoin effects.
• Nipolept (zotepine) - May increase the effects of phenytoin, dosage adjustments may be necessary.
• Non-Steroidal Anti-Inflammatories, or NSAIDs, such as Butazolidine (phenylbutazone), Clinoril (sulindac), Ibuprofen (Motrin), Indocin (indomethacin), Naprosyn (naproxen), Toradol (ketorolac), and others may increase phenytoin's effects.
• Norpace (disopyramide) - May be less effective when used with phenytoin.
• Oral contraceptives - Risk of contraceptive failure and breakthrough bleeding.
• Phenobarbitol - These medications may unpredictably interfere with each others blood levels.
• Phenurone (phenacemide) - Increased risk of Phenurone side effects.
• Platinol (cisplatin) - Phenytoin may be a less effective treatment in combination with this drug.
• Plavix (clopidogrel) - May increase phenytoin levels by interfering with removal from the body.
• Premarin and other conjugated estrogens may be less effective when used with phenytoin.
• Prilosec (omeprazole) - May increase the effects of phenytoin.
• Proglycem (diazoxide) - Do not combine.
• Protease inhibitors like Norvir (ritonavir), Zovirax (acyclovir), and possibly others may be less effective when used with phenytoin.
• Prograf (tacrolimus) - May be less effective when used with phenytoin.
• Proloprim (trimethoprim) - Can cause increased phenytoin levels.
• Quinaglute (quinidine) - May be less effective when used with phenytoin.
• Rapamune (sirolimus) - May be less effective when used with phenytoin.
• Rifadin (rifampin) - Phenytoin may be less effective, dose adjustment may be necessary.
• Ritalin (methylphenidate) - May change the pattern of seizure and necessitate dosage changes.
• Sandimmune (cyclosporine) - May be less effective when used with phenytoin.
• Selective serotonin reuptake inhibitors (SSRIs) like Celexa (citalopram), Paxil (paroxetine), Prozac (fluoxetine), Luvox (fluvoxamine), or Zoloft (sertraline) may alter blood levels of phenytoin. Your doctor will advise you if dosage adjustments are necessary or if blood levels will need to be more closely monitored.
• Seroquel (quetiapine) - May be less effective when used with phenytoin.
• Serzone (nefazodone) - May increase the effects of phenytoin.
• Sinemet (levodopa) - May be less effective when used with phenytoin.
• S-Liposomal doxorubicin - Phenytoin may build up in the body, dosage may need to be changed.
• Sulfonamides like Azulfidine (sulfasalazine), Gantanol (sulfamethoxazole), Renoquid (sulfacytine), Thiosulfil (sulfamethizole), and others, may cause phenytoin to build up in the body, increasing its effects.
• Synthroid (levothyroxine) - May not work as well when the treatments are combined.
• Tagamet (cimetidine) - May increase phenytoin levels.
• Taxol (paclitaxel) - May be less effective when used with phenytoin.
• Tegretol (carbamazepine) - May alter phenytoin levels, increasing or decreasing them.
• Tranquilizers such as Haldol (haloperidol), Mellaril (thioridazine), or Thorazine (chlorpromazine) may cause oversedation.
• Triamcinolone - May be less effective when used with phenytoin.
• Tricyclic antidepressants such as Elavil (amitriptyline), Asendin (amoxapine), Anafranil (clomipramine), Pertofrane or Norpramin (desipramine), Sinequan (doxepin), Tofranil (imipramine), Aventyl or Pamelor (nortriptyline), Vivactil (protriptyline), and Surmontil (trimipramine), may change seizure patterns or cause seizures in susceptible individuals. Your doctor will advise you if dosage adjustments are necessary or if blood levels will need to be more closely monitored.
• Wellbutrin, Zyban (bupropion) - May be less effective when used with phenytoin.
• Velban (vinblastine) - Phenytoin may not be as effective.
• Vibramycin (doxycycline) - May be less effective when used with phenytoin.
• Vitamin D (cholecalciferol) - May be less effective when used with phenytoin. Try to consume vitamin D enriched foods.

Cerebyx comes in a 10 ml vial containing 750 mg fosphenytoin sodium which has the equivalent effects of 500 mg phenytoin.

Cerebyx also comes in a 2 ml vial containing 150 mg fosphenytoin sodium which has the equivalent effects of 100 mg phenytoin.

Your doctor will prescribe a dosage based on your individual circumstances and medical condition. Follow your doctor's dosing instructions as they are given to ensure safe and effective treatment.

Cerebyx Directions

Follow your doctor's instructions carefully.

Store Cerebyx in the refrigerator at 36° to 46° F (2° to 8° C). Never allow medication to freeze. Do not use product if it contains particles or is discolored. Do not use after the expiration date.

Keep Cerebyx away from children; both when storing it, and when discarding any unused medication.

Cerebyx may cause drowsiness or disorientation, and you should familiarize yourself with your reaction to it before engaging in potentially hazardous activities. Be cautious if you plan to drive or operate heavy machinery, avoid these activities if you find yourself feeling tired or experience slowed reactions.

Carry identification so that emergency personnel will be aware that you take this drug.

Cerebyx and Pregnancy

Consult your doctor regarding the advisability of continuing this medication during pregnancy. Notify your doctor if you are pregnant or plan to become pregnant.

Cerebyx passes into breast milk in small amounts. If any adverse effects occur, discontinue breast feeding or Cerebyx treatment.

Cerebyx and Children

Children's tolerance of this medication varies widely. Frequent monitoring and individual dosage determinations are necessary for safe and effective treatment.

Watch carefully for unusual or jerky movements, clumsiness, and unusual behavior.

Cerebyx and Seniors

Seniors are likely to be more sensitive to this treatment, and should start out with the lowest possible dose. Watch carefully for altered vision, confusion, fatigue, sleepiness, slurred speech, twitching, and unsteadiness.

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Cerebyx is a trademark of Parke-Davis

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This document is provided for information only. It is not a substitute for consultation with a physician, either to diagnose symptoms or prescribe treatment. Any dosages mentioned are general guidelines only, please follow the directions of your doctor or pharmacist exactly when taking medication. We have made every effort to ensure that this information is accurate, but only your doctor can say if a medication, or drug combination, is safe for you. Information intended for US residents only.