Filgotinib: Selective JAK1 Inhibitor for Rheumatoid Arthritis and Ulcerative Colitis

Filgotinib (brand name Jyseleca, Galapagos and Alfasigma) is an oral Janus kinase inhibitor (JAK inhibitor) with preferential inhibition of the JAK1 isoform. EMA approval was granted in 2020 for moderate to severe active rheumatoid arthritis and in 2021 for moderate to severe active ulcerative colitis. Filgotinib thus belongs to the newer generation of targeted small molecule immunotherapy (targeted synthetic disease-modifying antirheumatic drugs, tsDMARD) that does not require intravenous administration.

The substance is part of a competitive market with Tofacitinib, Baricitinib, and Upadacitinib. Essential for clinical decision-making is the question of which JAK isoforms a drug more potently inhibits, because the safety profile and breadth of action depend on this. Filgotinib is considered JAK1 selective, which theoretically provides a more favorable profile for hematological effects and VTE risk, although data from large comparative studies are lacking.

Mechanism of Action

Janus kinases (JAK1, JAK2, JAK3, TYK2) are intracellular tyrosine kinases that bind to the intracellular domain of class I and II cytokine receptors. When a cytokine such as interleukin 6, interferon alpha, or interferon gamma binds to its receptor, the associated JAKs phosphorylate signal molecules of the STAT family. These migrate to the cell nucleus and regulate the transcription of proinflammatory genes.

Filgotinib inhibits JAK1 approximately 30 times more potently than JAK2 and 25 times more potently than JAK3. This preferential selectivity theoretically reduces effects on erythropoietin signaling pathways (JAK2) and lymphocyte development (JAK3). Clinically, filgotinib shows clear effects on rheumatoid arthritis within a few weeks, with ACR20/50/70 response comparable to Adalimumab and Tofacitinib in studies (FINCH 1 to 3).

Pharmacokinetically, filgotinib is converted to its active major metabolite GS 829845, which has a longer half-life. The combined effect allows once-daily oral administration.

Indications

• Moderate to severe active rheumatoid arthritis (RA): for inadequate response to conventional disease-modifying antirheumatic drugs or biologics, as monotherapy or combined with methotrexate
• Moderate to severe active ulcerative colitis: for inadequate response, intolerance, or contraindication for conventional therapy or biologics
• Off-label discussion: spondyloarthritis, psoriatic arthritis (approved for other JAK inhibitors in these indications)

Dosage and Administration

Standard dose: 200 mg once daily orally, with or without food. Dose adjustment: 100 mg for moderate renal impairment (creatinine clearance 15 to 60 ml/min); for severe renal impairment and dialysis, filgotinib is currently not recommended.

Elderly patients 75 years and older: EMA recommends special caution in this group and for rheumatoid arthritis preferably to consider alternatives, based on safety data from the ORAL Surveillance study with Tofacitinib. This recommendation was made in 2022 for the entire class of JAK inhibitors.

Severe hepatic impairment (Child Pugh C): not recommended due to insufficient data.

Adverse Effects

Frequent: upper respiratory tract infections, urinary tract infections, nausea, dizziness, headache, elevation of liver transaminases, lipid increase (LDL and HDL).

Occasional to rare, but important: herpes zoster reactivation, severe infections including opportunistic pathogens and tuberculosis reactivation, venous thromboembolism (deep vein thrombosis, pulmonary embolism), cardiovascular events (myocardial infarction, stroke), malignancies including lymphoma and skin cancer.

Important, EMA Safety Warning 2023: the class of JAK inhibitors is under increased safety surveillance. In patients with cardiovascular risk factors (hypertension, obesity, hyperlipidemia, smoking status, diabetes, previous cardiovascular events), known malignancy in history, or advanced age, filgotinib should only be used when no therapeutic alternatives are available.

Drug Interactions

• Other immunosuppressive agents (biologics, other JAK inhibitors, high-dose glucocorticoids): additive infection risk, avoid combination
• Live vaccines: contraindicated during therapy
• Rifampicin and other strong CYP3A4 inducers: reduced filgotinib levels, possible loss of efficacy
• Probenecid: filgotinib is excreted via OAT3, clinically relevant interaction rarely described but should be considered
• Methotrexate: combination is possible and tested in studies, note additive hepatotoxicity

Special Precautions

Pregnancy: contraindicated because filgotinib has shown testicular damage in animals in preclinical studies. Reliable contraception during and for at least one week after therapy completion. In men, therapy is currently not recommended for the reproductive phase; discussion with the treating rheumatologist is advisable.

Before therapy initiation: tuberculosis screening (IGRA test, chest X-ray), hepatitis B and C serology, HIV test, current vaccinations review, lipid status and blood count as baseline values.

Monitoring: blood count and liver transaminases at four and twelve weeks, lipid status at twelve weeks, thereafter individually. Patients must be informed about symptoms of unusual infections, signs of thrombosis, and cardiovascular warning symptoms.

You Might Also Be Interested In

• Tofacitinib, the first approved JAK inhibitor
• Baricitinib, JAK1/2 inhibitor
• Upadacitinib, another preferential JAK1 inhibitor
• Methotrexate, classic disease-modifying antirheumatic drug
• Adalimumab, TNF alpha antibody as alternative therapy

Frequently Asked Questions

Sources

• EMA, Jyseleca (Filgotinib) EPAR
• DGRh Guideline Rheumatoid Arthritis
• Gelbe Liste, Filgotinib Active Ingredient Profile
• BfArM, Dear Healthcare Professional Letter JAK Inhibitors 2023