SignalTrace

JAK Inhibitors

John Montgomery6 min read

JAK Inhibitors

Janus kinase (JAK) inhibitors are small-molecule drugs that block the JAK–STAT signalling inside immune cells. IL-4 and IL-13 from the Th2 Immune Response signal through JAK1/JAK2/TYK2 and STAT6 (Furue 2020, via Th2 Immune Response note). Unlike Dupilumab, which is an injected antibody against one receptor, JAK inhibitors act inside the cell, cut down several cytokine signals at once, and are taken as a tablet/liquid or applied as a cream. For Atopic Dermatitis they come in two groups. The oral ones are abrocitinib (Cibinqo), upadacitinib (Rinvoq) and baricitinib (Olumiant). The topical ones are Ruxolitinib Cream (Opzelura) and delgocitinib (Anzupgo in the EU and US; Corectim in Japan). For toddlers, the main points are age limits and the class boxed warning.

JAK Inhibitors [treats] Atopic Dermatitis JAK Inhibitors [opposes] Th2 Immune Response Ruxolitinib Cream [part-of] JAK Inhibitors JAK Inhibitors [relates] Dupilumab

Oral JAK inhibitors: ages 12+ (with one EU exception). In the US, abrocitinib and upadacitinib are licensed for refractory moderate-to-severe AD from age 12, when other systemic drugs, including biologics, have failed or are inadvisable (FDA labels, 2026). In the EU both are licensed from age 12 (EMA EPARs). Baricitinib is the outlier. The EMA licenses it for moderate-to-severe AD in adults and children from 2 years when topical treatment is not enough. This was based on a study of 483 children, in which 42% had clear or almost-clear skin at 16 weeks against 16% on placebo. Children had the same side effects as adults, except that neutropenia (low white cells) was common. An oral suspension is available, and tablets can be dissolved for children who cannot swallow them (EMA Olumiant EPAR). The US baricitinib label has no AD indication at all; it covers RA, COVID-19 and alopecia areata (FDA label, 2026). In trials of patients aged 12 and over, abrocitinib 200 mg gave clear or almost-clear skin in 38–44% against 8–9% on placebo at 12 weeks (EMA Cibinqo EPAR).

Conflict: [EMA Olumiant EPAR, accessed 2026-10-03] licenses oral baricitinib for moderate-to-severe AD in children from 2 years. [FDA Olumiant label, 2026] gives baricitinib no AD indication at any age. Unresolved — add to open_questions.

European Medicines Agency [regulates] JAK Inhibitors FDA [regulates] JAK Inhibitors JAK Inhibitors [relates] Systemic Immunosuppressants

Boxed warnings. In September 2021 the FDA required boxed warnings on tofacitinib, baricitinib and upadacitinib. The trigger was the ORAL Surveillance trial in RA patients aged 50 and over with cardiovascular risk factors, which found more heart attacks and strokes, cancer, blood clots and deaths than with TNF blockers (FDA Drug Safety Communication, 1 Sept 2021). Abrocitinib and the topical Ruxolitinib Cream label carry the same boxed warning: serious infections including TB and herpes zoster, mortality, malignancy (lymphoma and lung cancer), MACE and thrombosis (FDA labels, 2026). The labels require TB screening before oral treatment and advise against combining JAKs with biologics or other potent immunosuppressants. The data behind the warning come largely from older adults with RA, not young children. Whether the risks carry over to toddlers is unknown rather than shown to be absent.

Infection risk on JAK inhibitors

JAK inhibitors raise the risk of serious and opportunistic infections, including herpes infections. A child with eczema who is on a JAK inhibitor and develops sudden painful punched-out sores or a fever needs same-day review for Eczema Herpeticum.

FDA [regulates] JAK Inhibitors JAK Inhibitors [relates] Eczema Herpeticum JAK Inhibitors [relates] Herpes Simplex Virus

Topical JAK inhibitors: ruxolitinib and delgocitinib. On 18 September 2025 the FDA extended Ruxolitinib Cream 1.5% to children aged 2–11. It is for short-term, non-continuous treatment of mild-to-moderate AD in non-immunocompromised children when topical prescription therapies have not controlled it or are not advisable. The approval was based on the TRuE-AD3 trial in more than 300 children aged 2 to under 12 (Incyte release via Contemporary Pediatrics/AJMC; confirmed by the FDA label, 2026). Children aged 2–11 may use no more than one 60 g tube per 2 weeks, on no more than 20% of body surface area. In the EU, Opzelura is licensed for moderate AD in adults only (EMA EPAR). Delgocitinib cream (Anzupgo) is licensed in both the EU and US only for moderate-to-severe chronic hand eczema in adults (EMA EPAR; FDA label, 2026). Its Japanese licence for paediatric AD (Corectim, from 6 months) was not verified against a primary Japanese regulatory source this round.

Conflict: [FDA Opzelura label, 2026] licenses ruxolitinib cream for AD from age 2. [EMA Opzelura EPAR, accessed 2026-10-03] licenses it for AD in adults only. Unresolved — add to open_questions.

Ruxolitinib Cream [treats] Atopic Dermatitis JAK Inhibitors [relates] Topical Calcineurin Inhibitors JAK Inhibitors [relates] Crisaborole

Where they fit for a 1–4-year-old. For most toddlers, JAK inhibitors are not yet a realistic option. Under age 2 nothing is licensed. For ages 2–4, the steroid-sparing options licensed in the US are ruxolitinib cream (from 2), Crisaborole (from 3 months) and Topical Calcineurin Inhibitors. In the EU, oral baricitinib (from 2) sits alongside Dupilumab (from 6 months, severe AD) as a specialist systemic choice. No NICE or AAD paediatric guidance placing JAK inhibitors ahead of dupilumab in under-5s was found this round.

JAK Inhibitors [relates] Crisaborole Dupilumab [precedes] JAK Inhibitors

What parents report (evidence: anecdotal). Toddler-specific reports are rare. One parent says a paediatric dermatologist’s ruxolitinib cream (Opzelura) cleared a small patch “within days”, and now “whenever the eczema starts to come back we go straight to that” (r/Mommit). Oral JAK inhibitors come up only in adult threads. See Parent Experiences.

JAK Inhibitors [relates] Parent Experiences

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