Presently there are shortages of fosphenytoin (Cerebyx-R) due to glass particulate matter in some vials from one generic manufacturer and some manufacturers discontinuing the product. Information on this shortage may be found here.
Fosphenytoin may be available to some hospital pharmacies, but in the event it is not healthcare providers may need to switch to oral or intravenous phenytoin. Fosphenytoin is a more water soluble pro-drug of phenytoin, and because of this there are both differences and similarities.
Fosphenytoin may be given i.v. at a rate not to exceed 150 mg/minute, and may be given i.m. Blood pressure and EKG monitoring are still recommended. Owing to the presence of a phosphate group bonded to the phenytoin molecule, fosphenytoin is dosed in mg P.E. (phenytoin equivalents). I.E., if a phenytoin dose of 1000 mg is desired, the equivalent fosphenytoin dose is 1000 mg P.E. Additional important safety information may be obtained at the FDA website.
Intravenous phenytoin must be diluted only in normal saline (not D5W owing to crystal formation) and use of an in-line filter is recommended. I.V. phenytoin must never be administered at a rate exceeding 50 mg/minute owing to serious hypotension, requires blood pressure and EKG monitoring, should be given through a large-bore proximally placed i.v., may not be given i.m. because it may form sterile abscesses, and can cause thrombophlebitis (in rare cases, "purple glove syndrome").