The present invention is intended mainly to provide an external preparation that exerts a therapeutic and/or preventive effect against dermatological infections such as acne involving suppurative inflammation, and superficial infections of the skin upon being administered to a human patient once daily. For example, the present invention is an external preparation that comprises 1-cyclopropyl-8-methyl-7-[5-methyl-6-(methylamino)-3-pyridyl]-4-oxo-1,4-dihydro-3-quinolinecarboxylic acid and/or a pharmaceutically acceptable salt thereof as an active ingredient, and that exerts a therapeutic and/or preventive effect against a dermatological infection upon being administered to a human patient once daily.
