Enhanced purine salvage during allopurinol therapy: an important pharmacologic property in humans.

The contribution of enhanced purine salvage to the decreased total purine excretion associated with allopurinol therapy was measured by the intravenous administration of tracer doses of [8-(14)C] adenine to four patients with gout and normal purine salvage enzyme activity and four patients with the Lesch-Nyhan syndrome and absent purine salvage activity. The mean cumulative excretion of radioactivity 5 days after the adenine administration to patients not receiving and receiving (off and on) allopurinol therapy was 6.1% and 3.6% of infused radioactivity for gouty subjects and 15.9% and 20.8% for the Lesch-Nyhan patients. Urate pool size and urate turnover, as measured by pool labeling with [2-(14)C]uric acid, were substantially decreased in both groups of patients during allopurinol therapy. The intestinal loss of uric acid was estimated from these pool measurements on and off allopurinol. With a correction for this extrarenal purine loss, the mean cumulative excretions of radioactivity 5 days after adenine administration to patients off and on allopurinol therapy were 11.9% and 4.8% for the gouty subjects and 31.7% and 24.5% for the Lesch-Nyhan patients. In vitro studies demonstrated no alteration of the synthesis or degradation of adenine nucleotides by allopurinol in cultured human diploid fibroblasts. These observations suggest that enhanced purine salvage is an important component leading to decreased purine excretion during allopurinol therapy.