These first-generation JAKinibs comprise ruxolitinib, a JAK1 and JAK2 inhibitor, approved for myeloproliferative malignancies; tofacitinib, a JAK1, JAK2, JAK3 inhibitor, approved for rheumatoid arthritis, psoriatic arthritis, and ulcerative colitis; baricitinib, a JAK1 and JAK2 inhibitor, approved for rheumatoid arthritis; peficitinib, a pan-JAK inhibitor approved (only in Japan) for the treatment of rheumatoid arthritis; and oclacitinib, a JAK1 and JAK2 inhibitor, approved for allergic dermatitis in dogs (80). Here, JAK1 is linked to ulcerative colitis.