Fosphenytoin has been added to the DGMC Formulary and will replace Phenytoin IV as soon as existing stock is depleted.
1. Fosphenytoin (CEREBYX - Parke Davis) product labeling reflects the dose in phenytoin equivalents (PE) to simplify calculations (e.g. 500 mg phenytoin is equivalent to fosphenytoin 500 mg PE) The actual conversion, if it ever become necessary, is based upon 50 mg phenytoin = 75 mg fosphenytoin.
2. Fosphenytoin is water soluble, stable with most IV fluids (e.g. NSS, D5W, etc) and should be diluted to a final concentration of 1.5 to 25 mg PE per ml. Fosphenytoin should be stored under refrigeration. This product should not be stored at room temperature for more than 48 hours.
3. Fosphenytoin, unlike phenytoin, can be given IM - although the volume will be much larger than that normally administered via IM injection.
4. Initial dose is 15 to 20 mg PE/kg administered at 100 to 150 mg PE/min. �Because of the risk of hypotension, fosphenytoin should be administered no faster than 150 mg PE/minute 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 the infusion.
5 Common side effects include: hypotension, nystagmus, dizziness, pruritus, paresthesia, headache, somnolence, and ataxia. Paresthesia and pruritus (located in the face and groin areas) have been frequently reported but do not appear to be allergic reactions and typically resolve within 10 minutes after completion of infusion.
6. Fosphenytoin is Pregnancy Category D. It should also not be administered to nursing mothers. Use of fosphenytoin in pediatric patients �less then 5 years of age has not been established. No systemic studies in geriatric patients has been conducted. �Phenytoin clearance tends to decrease with age.