Probenecid appears to increase the
renal excretion of the active
metabolite of
allopurinol, while
allopurinol is thought to inhibit the
metabolism of
probenecid. Theoretically, the concurrent use of
allopurinol and
probenecid could lead to uric acid precipitation in the kidneys.
The
clinical significance of these interactions appears to be minimal. Nevertheless, the UK manufacturer of
allopurinol recommends any reduction in
efficacy should be assessed in each case. For
allopurinol injection, the US manufacturer recom- mends a high urinary output of at least 2 litres daily, and the maintenance of neutral or slightly alkaline urine, to help prevent
renal precipitation of urates.