Pharmaceutical composition comprising refined indigo naturalis extracts and the use thereof

A method of treating a disease or condition selected from the group consisting of psoriasis, an inflammatory disease, onychomycosis, skin cancer, abnormal keratinization induced disease, skin aging, and pustular dermatosis, comprising administering to a subject in need thereof a pharmaceutical composition comprising a solid extract of Indigo Naturalis, wherein the solid extract comprises, relative to the total weight of the extract:

• 65% to 90% (w/w) indirubin;
• 0.1-15% (w/w) indigo;
• and
• 0.01-5% (w/w) tryptanthrin,
• wherein the pharmaceutical composition comprises 0.002% to 0.077% (w/w) of the solid extract relative to the total weight of the pharmaceutical composition.