Generic name: FOSPHENYTOIN SODIUM 50mg in 1mL
Dosage form: injection, solution
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The dose, concentration, and infusion rate of CEREBYX should always be expressed as phenytoin sodium equivalents (PE). There is no need to perform molecular weight-based adjustments when converting between fosphenytoin and phenytoin sodium doses. CEREBYX should always be prescribed and dispensed in phenytoin sodium equivalent units (PE). 1.5 mg of fosphenytoin sodium is equivalent to 1 mg phenytoin sodium, and is referred to as 1 mg PE. The amount and concentration of fosphenytoin is always expressed in terms of mg of phenytoin sodium equivalents (mg PE).
Do not confuse the concentration of CEREBYX with the total amount of drug in the vial.
Caution must be used when administering CEREBYX due to the risk of dosing errors (see WARNINGS). Medication errors associated with CEREBYX have resulted in patients receiving the wrong dose of fosphenytoin. CEREBYX is marketed in 2 mL vials containing a total of 100 mg PE and 10 mL vials containing a total of 500 mg PE. Both vials contain a concentration of 50 mg PE/mL. Errors have occurred when the concentration of the vial (50 mg PE/mL) was misinterpreted to mean that the total content of the vial was 50 mg PE. These errors have resulted in two- or ten-fold overdoses of CEREBYX since each of the vials actually contains a total of 100 mg PE or 500 mg PE. In some cases, ten-fold overdoses were associated with fatal outcomes. To help minimize confusion, the prescribed dose of CEREBYX should always be expressed in milligrams of phenytoin equivalents (mg PE). Additionally, when ordering and storing CEREBYX, consider displaying the total drug content (i.e., 100 mg PE/ 2 mL or 500 mg PE/ 10 mL) instead of concentration in computer systems, pre-printed orders, and automated dispensing cabinet databases to help ensure that total drug content can be clearly identified. Care should be taken to ensure the appropriate volume of CEREBYX is withdrawn from the vial when preparing the dose for administration. Attention to these details may prevent some CEREBYX medication errors from occurring.
Prior to IV infusion, dilute CEREBYX in 5% dextrose or 0.9% saline solution for injection to a concentration ranging from 1.5 to 25 mg PE/mL. The maximum concentration of CEREBYX in any solution should be 25 mg PE/mL. When CEREBYX is given as an intravenous infusion, CEREBYX needs to be diluted and should only be administered at a rate not exceeding 150 mg PE/min.
Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration, whenever solution and container permit.
For single-use only. After opening, any unused product should be discarded.
- The loading dose of CEREBYX is 15 to 20 mg PE/kg administered at 100 to 150 mg PE/min.
- Because of the risk of hypotension, CEREBYX should be administered no faster than 150 mg PE/min. Continuous monitoring of the electrocardiogram, blood pressure, and respiratory function is essential and the patient should be observed throughout the period where maximal serum phenytoin concentrations occur, approximately 10 to 20 minutes after the end of CEREBYX infusions.
- Because the full antiepileptic effect of phenytoin, whether given as CEREBYX or parenteral phenytoin, is not immediate, other measures, including concomitant administration of an IV benzodiazepine, will usually be necessary for the control of status epilepticus.
- The loading dose should be followed by maintenance doses of either CEREBYX or phenytoin.
If administration of CEREBYX does not terminate seizures, the use of other anticonvulsants and other appropriate measures should be considered.
Even though loading doses of CEREBYX have been given by the IM route for other indications when IV access is impossible, IM CEREBYX should ordinarily not be used in the treatment of status epilepticus because therapeutic phenytoin concentrations may not be reached as quickly as with IV administration.
Nonemergent Loading and Maintenance Dosing
Because of the risks of cardiac and local toxicity associated with intravenous CEREBYX, oral phenytoin should be used whenever possible.
The loading dose of CEREBYX is 10 – 20 mg PE/kg given IV or IM. The rate of administration for IV CEREBYX should be no greater than 150 mg PE/min. Continuous monitoring of the electrocardiogram, blood pressure, and respiratory function is essential and the patient should be observed throughout the period where maximal serum phenytoin concentrations occur (approximately 20 minutes after the end of CEREBYX infusion).
The initial daily maintenance dose of CEREBYX is 4 – 6 mg PE/kg/day in divided doses. After administration of a loading dose, maintenance doses should typically be started at the next identified dosing interval.
IM or IV Substitution For Oral Phenytoin Therapy
When treatment with oral phenytoin is not possible, CEREBYX can be substituted for oral phenytoin at the same total daily phenytoin sodium equivalents (PE) dose. Dilantin capsules are approximately 90% bioavailable by the oral route. Phenytoin, supplied as CEREBYX, is 100% bioavailable by both the IM and IV routes. For this reason, plasma phenytoin concentrations may increase modestly when IM or IV CEREBYX is substituted for oral phenytoin sodium therapy. The rate of administration for IV CEREBYX should be no greater than 150 mg PE/min. In controlled trials, IM CEREBYX was administered as a single daily dose utilizing either 1 or 2 injection sites. Some patients may require more frequent dosing.
Dosing in Special Populations
Patients with Renal or Hepatic Disease
Due to an increased fraction of unbound phenytoin in patients with renal or hepatic disease, or in those with hypoalbuminemia, the interpretation of total phenytoin plasma concentrations should be made with caution (see CLINICAL PHARMACOLOGY: Special Populations). Unbound phenytoin concentrations may be more useful in these patient populations. After IV CEREBYX administration to patients with renal and/or hepatic disease, or in those with hypoalbuminemia, fosphenytoin clearance to phenytoin may be increased without a similar increase in phenytoin clearance. This has the potential to increase the frequency and severity of adverse events (see PRECAUTIONS).
Age does not have a significant impact on the pharmacokinetics of fosphenytoin following CEREBYX administration. Phenytoin clearance is decreased slightly in elderly patients and lower or less frequent dosing may be required.