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. Provided is a pharmaceutical composition containing, as an active ingredient, a compound represented by formula (I) or a pharmacologically acceptable salt thereof. In the formula (I), R1 and R2 are the same or different, and represent a C1-C6 alkyl group, a halogeno C1-C6 alkyl group or a C3-C6 cycloalkyl group； n represents 0, 1 or 2； each X represents a C1-C6 alkyl group, a C3-C6 cycloalkyl group, a halogen atom or the like； and Y represents a hydrogen atom, a C1-C6 alkoxy group, a C3-C6 cycloalkoxy group or a halogeno C1-C6 alkoxy group.
