The present invention provides a transdermal drug delivery system which comprises: a therapeutically effective amount of a non-steroidal anti-inflammatory drug; at least one dermal penetration enhancer, which is a safe skin-tolerant ester sunscreen ester; and at least one volatile liquid. The invention also provides a method for administering at least one systemic or locally acting non-steroidal anti-inflammatory drug to an animal which comprises applying an effective amount of the non-steroidal anti-inflammatory drug in the form of the drug delivery system of the present invention.