Janus Kinase (JAK) Inhibitors

Reviewed by: HU Medical Review Board | Last reviewed: June 2022 | Last updated: August 2022

Janus kinase (JAK) inhibitors are a new class of drugs used to treat moderate to severe atopic dermatitis (the most common form of eczema). These drugs may be used topically (on the skin) or taken orally (by mouth).1-3

Before 2021, JAK inhibitors were only used to treat some chronic inflammatory conditions, such as rheumatoid arthritis and ulcerative colitis.1-3

How do JAK inhibitors work?

Cytokines are immune system messengers that cause inflammation. People with eczema have higher levels of cytokines. Some cytokines use pathways called the Janus Kinase-Signal transducer and activators of transcription (JAK-STAT). Cytokines use these pathways to drive abnormal immune responses in conditions like atopic dermatitis.2,3

JAK inhibitor drugs block overactive JAK pathways. This lowers the cytokines that turn on eczema symptoms like redness, itching, and inflammation.2,3

JAK inhibitors for atopic dermatitis (eczema)

The JAK inhibitors currently approved by the U.S. Food and Drug Administration (FDA) to treat atopic dermatitis are:1,4,5

Baricitinib is another JAK inhibitor for eczema being studied in a clinical trial.1-3

Other JAK inhibitors are expected to be developed in the next several years since the JAK pathway is a major area of drug study.2,3

What are the possible side effects of JAK inhibitors?

Side effects can vary depending on the specific drug you are taking. Generally, common side effects of JAK inhibitors include:1-4

  • Nausea
  • Swelling of the nasal passages and back of the throat
  • Diarrhea
  • Headache
  • Upper respiratory infections

These are not all the possible side effects of JAK inhibitors. Talk to your doctor about what to expect when taking a JAK inhibitor. You should also call your doctor if you have any changes that concern you when taking one of these drugs.

Things to know about JAK inhibitors

JAK inhibitors work on the immune system. They can lower your body’s ability to fight infections. Your doctor will monitor you for signs of infection during and after treatment with these drugs. Get medical help right away if you have signs of an infection, including:3,4

  • Fever
  • Muscle pain
  • Cough
  • Shortness of breath
  • Diarrhea
  • Extreme tiredness
  • Pain while urinating

There is an increased risk of heart attack, stroke, or death in people with risk factors who smoke or used to smoke while using JAK inhibitors. Seek medical help right away if you have any of these symptoms:3,4

  • Chest pain or tightness
  • Pain in the chest, throat, neck, or jaw
  • Shortness of breath
  • Cold sweats
  • Nausea
  • Vomiting
  • Weakness on 1 side of the body
  • Slurred speech.

JAK inhibitors can cause blood clots in leg veins. This is called deep vein thrombosis (DVT). These clots can travel to the lungs. This is called pulmonary embolism (PE). DVT and PE can be life-threatening. Get medical help right away if you have any of these symptoms:3,4

  • Pain
  • Swelling or tenderness in the leg(s)
  • Sudden chest or upper back pain
  • Shortness of breath.

JAK inhibitors can cause low blood cell counts. Your doctor will order lab tests during treatment. Tell your doctor if you have unusual bruising or bleeding, shortness of breath, fever, or tiredness.3,4

Before beginning treatment for atopic dermatitis (eczema), tell your doctor about all your health conditions and any other drugs, vitamins, or supplements you take. This includes over-the-counter drugs.

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