An object of the present invention is to find a novel pharmaceutical that has an excellent tryptophanase inhibitory effect, and suppresses worsening of renal function to preserve the kidney by reducing production of indoxyl sulfate in the blood. The present invention provides a pharmaceutical composition containing, as an active ingredient, a compound represented by the following formula, or a pharmacologically acceptable salt thereof:wherein R1 and R2 are the same or different, and represent a C1-C6 alkyl group or the like, and Ar represents an optionally substituted phenyl group or an optionally substituted thienyl group.
