Allopurinol in renal failure and the tumour lysis syndrome

This paper illustrates several important points relating to the use of allopurinol in renal failure, or situations of purine overproduction: It is very easy to give too much allopurinol. Most of the side effects (bone marrow depression, exfoliative dermatitis, etc) are the result of overdosage due to the retention of oxipurinol, an effect exaggerated by thiazide diuretics. Monitoring of plasma oxipurinol levels (ideally less than 100 mumol/l) by high-pressure liquid chromatography is helpful for adjusting dosage in renal failure. Some estimate of the anticipated purine excess is equally vital in deciding dosage during tumour lysis if the risk of urate nephropathy is not to be substituted for the certainty of xanthine nephropathy. In this situation the use of allopurinol may even be questioned. Patients with HGPRT deficiency are exquisitely sensitive to allopurinol, and careful monitoring of the effect on urinary purine levels is essential if xanthine colic is to be avoided.