Simple explanation
The immune system communicates using chemical messengers called cytokines.
Some cytokines activate signaling pathways that contribute to inflammation. These signals can become excessive or dysregulated in diseases such as rheumatoid arthritis, atopic dermatitis and alopecia areata.
Baricitinib blocks specific enzymes involved in transmitting these signals.
The JAK pathway
JAK stands for Janus kinase.
The JAK family includes:
- JAK1
- JAK2
- JAK3
- TYK2
Baricitinib primarily inhibits JAK1 and JAK2.
These enzymes participate in signaling from multiple cytokine receptors. Blocking JAK signaling can reduce downstream inflammatory gene activity.
Why this matters
In rheumatoid arthritis, persistent immune signaling contributes to:
- Synovial inflammation
- Joint swelling
- Pain
- Stiffness
- Progressive structural damage
Reducing inflammatory signaling can improve disease activity.
In atopic dermatitis, immune signaling contributes to skin inflammation and symptoms such as itching and lesions.
In alopecia areata, abnormal immune activity targeting hair follicles contributes to hair loss.
EMA describes baricitinib as reducing inflammation in rheumatoid arthritis, atopic dermatitis, alopecia areata and juvenile idiopathic arthritis by blocking Janus kinase activity.
Why baricitinib is different from biologic DMARDs
Baricitinib is a small-molecule oral medicine.
Many biologic DMARDs are large protein medicines administered by injection or infusion and target specific extracellular molecules.
Baricitinib instead acts intracellularly on JAK signaling pathways.