PROTEIN NITROGEN UNITS

[gschadow]

Requested for FDA/CBER in order to support biologic structured product labeling:

PROTEIN NITROGEN UNITS (typically abbreviated "PNU") - A potency unit based on the micro-Kjeldahl measurement of protein nitrogen in an acid precipitated extract. Typically, 1 mg of protein nitrogen equals 100,000 PNU.

See also #17 and #18

[gschadow]

The definition is not sufficient to establish this notion as a unit.

This could be a good unit, since a reference to mass is given, although I am worried about the adverb "typically".

Will ask for literature reference.

[gschadow]

Protein Nitrogen Unit Precipitation Procedure for Allergenic Extracts

[gschadow]

The May JACI paper says

"One PNU/ml is equivalent to 1 x 10^-5 mg of nitrogen determined to be in the material precipitated from 1 ml of allergenic extract by phosphotungstic acid (PTA)"

no mention of "typically" here. So is 1 PNU simply 10^-5 mg? PNU is first and foremost a kind of quantity: amount of protein-nitrogen. Thus defined, it would work. But, when used to specify the quantity of an ingredient without the chance to say the kind of quantity, we can't do it.

This is a problem.

[gschadow]

Optimization of parameters in protein nitrogen unit precipitation procedure for allergenic extracts

[gschadow]

Statement by submitter:

"The PNU unit is an old protein unit unrelated to SI units. Several hundred products, from several manufacturers, are labeled in PNUs, and a switch to SI units for protein content is impractical."

I wish we could simply add it. May be we can. May be we have to define special (arbitrary) units with a link to the procedure? This is what IUPAC C-NPU calls "procedure defined unit". That could be the way out.

[gschadow]

Because it's an equivalent, we can't really put it into the dimension of mass. But we can't run away from it. See #18 for discussion.

Provisionally accepted as [PNU]