[The uricosuric effect of benzbromaron and probenecid under fasting conditions (author's transl)].

As we could demonstrate in a group of 39 obese subjects submitted to a 15-days period of absolute fasting, the developing hyperuricemia coincides with a decrease of uric acid clearance following an increase of the reabsorbed amount of filtered uric acid. After daily application of 2 g probenecid a marked uricosuric effect was detectable only during the first 3 days, while in the following time this effect was perceptible only impaired. As a reason for the diminution of efficacy the fasting-dependent urinary acidosis is discussed, which leads to low tubular concentration of the pharmacon by non ionic diffusion. In a dosage of 100 and 300 mg/day benzbromaron proved to be a much more potent uricosuricum. Additionally, related to the increase of dose the unproportional strong fall of serum uric acid levels, which stood in contrast to higher rations of uric acid excretion under a lower dose and which exceeded the dose-depending increase of uric acid clearance, indicated an additional extrarenal site of action. The depression of PAH-excretion after application of 2 g/day probenecid, which comes about the competitive inhibition, did not occur under 100 mg/day benzbromaron. This difference signifies, that benzbromaron does not develop its uricosuric effect by influencing the tubular transport system, which is specific for PAH and probenecid.