Bioequivalence of allopurinol-containing tablet preparations

The study was undertaken to prove the bioequivalence of two allopurinol tablet preparations.

The relative bioavailability of allopurinol from two tablet preparations (Uribenz vs. Zyloric 300) was estimated on 18 volunteers of both sexes in an open randomized study by administering one tablet of each preparation at an interval of 2 weeks. The plasma concentrations of allopurinol and its active metabolite oxypurinol were measured over a time-period of 72h by HPLC.

While the mean AUC(0-72) values of allopurinol and oxypurinol after the test and reference preparations are entirely identical (5.33 vs. 5.21 and 137.95 vs. 137.96 microg h ml(-1), respectively), the C(max) values of oxypurinol unlike those of allopurinol show small differences (4.59 vs. 4.78 and 1.91 vs. 193 microg/ml, respectively). According to the parametric and non-parametric analysis, the quotients AUC(T)/AUC(R) and C(maxT)/C(maxR) lie within the confidence intervals 0.8 to 1.2 and 0.7 to 1.3 respectively With regard to the t(max) of allopurinol, the differences of test and reference preparations are between 0.10 to 0.05h and of oxypurinol between -0.10 to 0.87h (parametric analysis). Both, Uribenz 300 and Zyloric 300 caused a maximum decrease of the uric acid concentration in the volunteers by 18% after 10 and 24h, respectively.

Thus the bioequivalence of the allopurinol tablet preparations is demonstrated.