Note on the enzyme assay for urinary D-glucaric acid and correlation with rifampicin-induced mixed function oxidase activity.

The enzyme assay for urinary D-glucaric acid is the simplest specific procedure for measuring drug-mediated hepatic enzyme induction in an ordinary laboratory without complex equipment. The problem of lactone conversion and interfering substances in the urine is examined. The normal range showed no significant difference between males (mean +/- SD = 42.60 +/- 19.80 mumol/day) and females (mean +/- SD = 40.40 +/- 31.50 mumol/day). Storage of urine at -20 degrees C longer than 6 months caused a decline in recovery probably due to further breakdown of D-glucarate. During rifampicin/streptomycin treatment a negative correlation was found between decline in antipyrine half-life (t1/2), a measure of mixed function oxidase activity, and rise in urinary D-glucaric acid (r = -0.7614, p less than 0.05). However, in 63 patients receiving rifampicin/isoniazid therapy no rise in D-glucaric acid was detected. Isoniazid appears to be an inhibitor of the glucuronic acid pathway in man at the level of uronlactonase or glucuronolactone dehydrogenase.