Please add “[mgPE]” for “milligrams of Phenytoin Equivalents”

[Paul Schluter]

Fosphenytoin is a prodrug of phenytoin. Because the molecular weight differences, 1 mg of fosphenytoin is not equal to 1 mg of phenytoin. To avoid dosing confusion, the recommended dosing unit for fosphentyoin is mgPE (i.e. no dosing adjustments are needed using mgPE). This UOM would be limited to only fosphenytoin and other prodrugs of phenytoin.

The FDA stipulates the following guidance regarding phenytoin sodium equivalents (PE) in ​https://www.accessdata.fda.gov/drugsatfda_docs/label/2007/076886s000lbl.pdf :

“IMPORTANT NOTE: Throughout all fosphenytoin product labeling, the amount and concentration of fosphenytoin is expressed in terms of phenytoin sodium equivalents (PE). Fosphenytoin’s weight is expressed as phenytoin sodium equivalents to avoid the need to perform molecular weight-based adjustments when converting between fosphenytoin and phenytoin sodium doses. Fosphenytoin should always be prescribed and dispensed in phenytoin sodium equivalent units (PE). (See DOSAGE AND ADMINISTRATION.)”

Although the proposed [mgPE] unit is primarily intended for drug administration rather than laboratory observations, Table 19 in §45 chemical and biochemical units would be the most appropriate location for this unit. Although [mgPE] is specific to phenytoin and related prodrugs used for pharmacy dispensing, it is viewed as an essential addition to both UCUM and IEEE 11073 by the IHE Patient Care Device (PCD) community.

The suggested entries in Table 19 in §45 chemical and biochemical units are shown below but are certainly open for further discussion.

name	milligrams of phenytoin sodium equivalents
kind of quantity	mass equivalent (of a prodrug of phenytoin)
print	mgPE
c/s	[mgPE]
c/I	[MGPE]
M	no
definition value
definition unit

Examples of use:

English: drug strength is “50 mg PE/mL” with the note (PE=phenytoin sodium equivalents)
UCUM: value = 50, units = [mgPE]/mL

English: a single dose of “400 mg PE”
UCUM: value = 400, units = [mgPE]

[Brenée Mitchell]

Hi Paul,

Thank you for the request and supporting information. We will discuss the addition of mgPE to the UCUM standard at our next committee meeting, which has yet to be scheduled. I will keep you up to date with any questions the committee has and/or what the final decision is.

Thanks again, Brenee Mitchell Regenstrief Institute/LOINC

Replying to Paul Schluter:

Fosphenytoin is a prodrug of phenytoin. Because the molecular weight differences, 1 mg of fosphenytoin is not equal to 1 mg of phenytoin. To avoid dosing confusion, the recommended dosing unit for fosphentyoin is mgPE (i.e. no dosing adjustments are needed using mgPE). This UOM would be limited to only fosphenytoin and other prodrugs of phenytoin.

The FDA stipulates the following guidance regarding phenytoin sodium equivalents (PE) in ​https://www.accessdata.fda.gov/drugsatfda_docs/label/2007/076886s000lbl.pdf :

“IMPORTANT NOTE: Throughout all fosphenytoin product labeling, the amount and concentration of fosphenytoin is expressed in terms of phenytoin sodium equivalents (PE). Fosphenytoin’s weight is expressed as phenytoin sodium equivalents to avoid the need to perform molecular weight-based adjustments when converting between fosphenytoin and phenytoin sodium doses. Fosphenytoin should always be prescribed and dispensed in phenytoin sodium equivalent units (PE). (See DOSAGE AND ADMINISTRATION.)”

Although the proposed [mgPE] unit is primarily intended for drug administration rather than laboratory observations, Table 19 in §45 chemical and biochemical units would be the most appropriate location for this unit. Although [mgPE] is specific to phenytoin and related prodrugs used for pharmacy dispensing, it is viewed as an essential addition to both UCUM and IEEE 11073 by the IHE Patient Care Device (PCD) community.

The suggested entries in Table 19 in §45 chemical and biochemical units are shown below but are certainly open for further discussion.

name	milligrams of phenytoin sodium equivalents
kind of quantity	mass equivalent (of a prodrug of phenytoin)
print	mgPE
c/s	[mgPE]
c/I	[MGPE]
M	no
definition value
definition unit

Examples of use:

English: drug strength is “50 mg PE/mL” with the note (PE=phenytoin sodium equivalents)
UCUM: value = 50, units = [mgPE]/mL

English: a single dose of “400 mg PE”
UCUM: value = 400, units = [mgPE]