The present invention describes novel compounds, or their pharmaceutically acceptable salts, pharmaceutical compositions containing them, and their medical uses. The compounds of the invention have activity as Janus Kinase inhibitors and are useful in the treatment or control of pruritus, associated with allergic dermatitis, atopic dermatitis in animals, and other disorders and indications where immunosuppression/immunomodulation would be desirable. Also described herein are methods of treating pruritus and atopic dermatitis by administering the compounds of the invention, which are JAK 1 inhibitors.