2007 Volume 20 Issue 1 Pages 9-13
There is not a strong correlation between dosage and blood concentration of mizoribine, an immunosuppressive agent used for pediatric kidney diseases such as nephrotic syndrome. Therefore, we considered that there are differences in the bioavailability of mizoribine between individuals. In addition, the quantity of urinary excretion for mizoribine is thought to be equal to that of intestinal absorption, because it is excreted by the kidney without sustained metabolism of all of the mizoribine absorbed in the bowel. We gave pediatric kidney disease patients mizoribine and examined the blood concentration and quantity of urinary excretion. The urinary excretion rate was 32.2±19.3% (n=15, 8.7%∼86.5%) for 24 hours. Ibara reported a urinary excretion rate of 55.4±17.7% (30.0%∼79.8%) in adults with rheumatoid arthritis. There was a marked difference between their findings and our results, which we attributed to lower intestinal absorption rates in children than in adults. There was a correlation (R2=0.60, p=0.0008) between AUCinf (dosage was converted to 1mg/kg) and urinary excretion rate (%). There was also a correlation (R2=0.31, p=0.03) between age and urinary excretion rate. It is thought that one of the causes of the differences between individuals in bioavailability of mizoribine is age-related, and it seems that high dose mizoribine administration is required to obtain an adequate blood concentration in younger children.
