Hyperammonemic crises in patients with urea cycle disorders on chronic nitrogen scavenger therapy with either sodium phenylbutyrate or glycerol phenylbutyrateAuthor(s): Jeffrey D Kent, Robert J Holt
Hyperammonemic crises (HACs) in patients with urea cycle disorders (UCDs) are associated with mortality and intellectual/cognitive decline. Fasting ammonia correlates with daily ammonia exposure and the risk and rate of HACs. UCD patients receiving sodium phenylbutyrate (NaPBA) and switched to glycerol phenylbutyrate (GPB) in three short-term comparative studies were examined over a 12-month period during dosing with GPB to identify characteristics associated with HACs.
UCD patients completing long term studies (n=100) and those who had HACs were examined for the following: 1) Demographics, 2) Incidence and rate of HAC, 3) Time to first HAC, and 4) Duration of, and hospitalization for, HACs. Comparisons were reported for the pre-study and the 12 month follow-up study.
The percentage of people experiencing a HAC in the study was 19%. HAC risk was 5-7 times higher in those reporting the higher ammonia levels compared to lower levels. Significant reductions in HACs were noted in the long term follow-up as compared to the pre-study period in both pediatric and the overall population. During pre-study, 44% of pediatric patients had experience at least one HAC as compared with 25% of children experiencing a HAC during the long term follow-up while on GPB and a higher proportion of males experienced a HAC in the pre-study period (42%) compared to females (24%). The mean duration of a HAC was just under 2 days and hospitalizations were more frequent in the pre-study period. Ammonia levels were higher during hospitalization in the pre-study period but by discharge they were not different.
UCD patients on chronic nitrogen scavenging therapy showed an overall incidence of HACs of 20%, with rates higher with increased ammonia exposure. HAC rate was lower with long term treatment with GPB as compared to pre-study treatment with NaPBA in both pediatric and the overall population studied.