A method of treating a patient suffering from a condition or disorder selected from chronic pain, neuropathic pain, fibromyalgia, migraine, bipolar disorder and depression comprises the administration of a pharmacologically effective amount of 3-(phenylmethylamino-methylene)pyrrolidine-2,4-dione (I) or a pharmaceutically acceptable salt or prodrug or solvate thereof. Also disclosed is the use of (I) for the manufacture of a pharmaceutical composition for treatment of such condition or disorder.