Ammonia metabolism in Reye syndrome and the effect of citrulline

Ammonia metabolism in Reye syndrome was studied by quantitative analysis of the time course of hyperammonemia and the urinary excretion of ammonia, urea, and total nitrogen. These measures were then utilized to assess the effect of citrulline administration in 8 patients compared to results in 22 patients managed without citrulline. Two indices of the severity and duration of hyperammonemia correlated strongly with mortality: the half-time for decline of hyperammonemia and the area under the hyperammonemia curve (an index of the total burden of ammonia presented to the brain). These results suggest that the total amount of ammonia delivered to brain may be important to the pathogenesis of encephalopathy. Citrulline-treated patients had more severe disease at admission and greater abnormalities in indices of nitrogen and ammonia metabolism, though the latter did not reach significance. The urine ammonia/urea nitrogen excretion ratio, an index of the efficiency of ammonia conversion to urea, normalized more rapidly in the citrulline-treated group, evidence that citrulline may have improved urea cycle function. Overall mortality did not differ in the two groups. The deaths of 2 citrulline-treated patients in this small group were attributable to factors unrelated to treatment, however, so the possible effect of citrulline on mortality was not definitively tested. No indication was found that citrulline was harmful, nor that it increased ammonia levels.