Protein substitute dosage in PKU: how much do young patients need?
BACKGROUND
The optimal dose of protein substitute has not been determined in children with phenylketonuria (PKU).


OBJECTIVE
To determine if a lower dose of protein substitute could achieve the same or better degree of blood phenylalanine control when compared to the dosage recommended by the UK MRC.(1)


METHODS
In a six week randomised, crossover study, two doses of protein substitute (Protocol A: 2 g/kg/day of protein equivalent; Protocol B: 1.2 g/kg/day protein equivalent) were compared in 25 children with well controlled PKU aged 2-10 years (median 6 years). Each dose of protein substitute was taken for 14 days, with a 14 day washout period in between. Twice daily blood samples (fasting pre-breakfast and evening, at standard times) for plasma phenylalanine were taken on day 8-14 of each protocol. The median usual dose of protein substitute was 2.2 g/kg/day (range 1.5-3.1 g/kg/day).


RESULTS
When compared with control values, median plasma phenylalanine on the low dose of protein substitute increased at pre-breakfast by 301 mumol/l (95% CI 215 to 386) and in the evening by 337 micromol/l (95% CI 248 to 431). On the high dose of protein substitute, plasma phenylalanine concentrations remained unchanged when compared to control values. However, wide variability was seen between subjects.


CONCLUSIONS
A higher dosage of protein substitute appeared to contribute to lower blood phenylalanine concentrations in PKU, but it did have a variable and individual impact and may have been influenced by the carbohydrate (+/- fat) content of the protein substitute.
MacDonald
A
A
Birmingham Children's Hospital, Birmingham, UK. anita.macdonald@bch.nhs.uk
Chakrapani
A
A
Hendriksz
C
C
Daly
A
A
Davies
P
P
Asplin
D
D
Hall
K
K
Booth
I W
IW
D002648:Child; D002675:Child, Preschool; D018592:Cross-Over Studies; D018753:Diet, Protein-Restricted; D004044:Dietary Proteins / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D008297:Male; D010649:Phenylalanine / Q000008:administration & dosage / Q000097:blood*; D010661:Phenylketonurias / Q000097:blood / Q000178:diet therapy*; D011446:Prospective Studies
D004044:Dietary Proteins; D010649:Phenylalanine