The present invention relates to a pharmaceutical composition comprising a sulfonamide as an inhibitor of Bcl-2/Bcl-xL, especially compound (3R)-1-(3-(4-(4-(4-(3-(2-(4-chlorophenyl)-1-isopropyl-4-methylsulfonyl-5-methyl-1H-pyrrol-3-yl)-5-fluorophenyl)piperazin-1-yl)-phenylaminosulfonyl)-2-trifluoromethyl sulfonyl-anilino)-4-phenylthio-butyl)-piperidine-4-carboxylic acid 3-phosphonopropyl ester or a pharmaceutically acceptable salt thereof and suitable excipients, preferably a pharmaceutical composition in the form of a lyophilized powder. The invention also relates to a method for preparing the pharmaceutical composition.