Ritlecitinib

Table of contents

• What is ritlecitinib?
• How does ritlecitinib work?
• Which conditions is ritlecitinib used or studied for?
• How is ritlecitinib given?
• What do the clinical trials show?
• What side effects are known?

What is ritlecitinib?

Ritlecitinib is a chemically synthesised, small-molecule medicine that belongs to a class of drugs called Janus kinase (JAK) inhibitors. It is the active substance in Litfulo 50 mg hard capsules, a medicine authorised in the European Union and the United States.^[5][2] The European Medicines Agency (EMA) authorised Litfulo in 2023 for treating severe alopecia areata, an autoimmune disease that causes hair loss on the scalp or other parts of the body.^[5] The marketing authorisation in the EU is held by Pfizer Europe MA EEIG.^[1] In the EU clinical trial registry, the substance carries the ATC code L04AF08, which places it among immunosuppressants.^[1]

How does ritlecitinib work?

Ritlecitinib is an immunosuppressant, meaning it reduces the activity of the immune system. It works by blocking the action of enzymes called JAK3 and TEC kinases, which play an important role in inflammation.^[5] In alopecia areata, the immune system attacks hair follicles, causing hair growth to slow or stop. By blocking these enzymes, ritlecitinib reduces inflammation, which allows hair regrowth in people with this condition.^[5] The same anti-inflammatory mechanism is being explored in vitiligo, where the immune system attacks pigment-producing cells in the skin.^[1]

Which conditions is ritlecitinib used or studied for?

• Severe alopecia areata — an authorised use. Ritlecitinib is approved in the EU and US for adults and adolescents aged 12 and over with this autoimmune disease, which causes hair loss on the scalp or elsewhere on the body.^[5][2]
• Vitiligo — an investigational use. A Phase 2 trial is studying whether ritlecitinib, alone or combined with narrowband ultraviolet B (nbUVB) light therapy, can improve skin repigmentation in people with vitiligo.^[1]

How is ritlecitinib given?

Ritlecitinib is given by mouth as a hard capsule. The authorised product, Litfulo, is available as 50 mg capsules taken once daily.^[5][2] In the vitiligo trial, the intervention is described as Litfulo 50 mg hard capsules at a 100 mg dose taken orally.^[1] The NHS dm+d browser, a UK medicines database, lists ritlecitinib as an ingredient but notes that no virtual medicinal products were available for it at the time of the record.^[4]

What do the clinical trials show?

The EU Clinical Trials Information System lists one Phase 2 trial of ritlecitinib in vitiligo, with the status Authorised.^[1] The trial plans to enrol 80 participants and compares two approaches: ritlecitinib alone versus ritlecitinib combined with narrowband ultraviolet B light therapy (nbUVB).^[1] The main measure is the percentage change from baseline in the Facial Vitiligo Area Scoring Index (F-VASI) at week 52. F-VASI is a tool that assesses the extent of depigmentation on the face using fingertip units (FTU).^[1] The trial also compares the mean percentage change in F-VASI and the Total Vitiligo Area Scoring Index (T-VASI) between baseline and week 52.^[1]

What side effects are known?

The US prescribing information for Litfulo carries a boxed warning about serious risks, including serious bacterial, fungal, viral and opportunistic infections that may lead to hospitalisation or death, including tuberculosis. Treatment should be interrupted if a serious infection occurs until the infection is controlled.^[2] Malignancies, major adverse cardiovascular events such as heart attack and stroke, and thrombosis including pulmonary embolism have been reported in people treated with ritlecitinib.^[2] The Italian Medicines Agency (AIFA) has issued a Direct Healthcare Professional Communication on Litfulo, which is a safety communication distributed to healthcare professionals.^[3] The EMA product information states that treatment should be interrupted or stopped if patients experience serious infections or low blood cell levels, and stopped if no improvements are seen after 36 weeks.^[5]