The present invention addresses the problem of finding a novel medicine which has an excellent tryptophanase inhibitory effect, suppresses indoxyl sulfate production in blood to thereby prevent deterioration of renal function, and thus contributes to kidney preservation. Provided is a medicinal composition which comprises a compound represented by the formula or a pharmacologically acceptable salt thereof as an active ingredient. (In the formula: R1 and R2 may be the same or different and represent a C1-C6 alkyl group, etc.； and Ar represents an optionally substituted phenyl group or an optionally substituted thienyl group.)
