Last reviewed 2026-04-20 · How we verify

Litfulo (Ritlecitinib Tosylate)

Ritlecitinib irreversibly inhibits JAK3 and TEC kinase family by blocking ATP binding site.

LITFULO (ritlecitinib tosylate) is a JAK3/TEC kinase inhibitor approved for severe alopecia areata in patients 12 years and older. The drug demonstrates dose-proportional pharmacokinetics with rapid absorption (Tmax 1 hour), moderate protein binding (14%), and short half-life (1.3-2.3 hours), requiring metabolism through multiple pathways. Key risks include CYP3A and CYP1A2 inhibition requiring dose adjustments of concomitant substrates, and contraindication in patients with hypersensitivity or severe hepatic impairment. Not recommended for combination use with other JAK inhibitors, biologic immunomodulators, cyclosporine, or potent immunosuppressants.

At a glance

Mechanism of action

Ritlecitinib is a kinase inhibitor that irreversibly inhibits JAK3 and the TEC kinase family by blocking the adenosine triphosphate (ATP) binding site. In cellular settings, ritlecitinib inhibits cytokine-induced STAT phosphorylation mediated by JAK3-dependent receptors and inhibits signaling of immune receptors dependent on TEC kinase family members. The relevance of inhibition of specific JAK or TEC family enzymes to therapeutic effectiveness is not currently known.

Approved indications

• Alopecia areata

Common side effects

• Headache
• Diarrhea
• Acne
• Rash
• Urticaria
• Folliculitis
• Pyrexia
• Dermatitis atopic
• Dizziness
• Blood creatine phosphokinase increased
• Herpes zoster
• Red blood cell count decreased

Drug interactions

• CYP3A substrates (where small concentration changes may lead to serious adverse reactions)
• CYP1A2 substrates (where small concentration changes may lead to serious adverse reactions)
• Strong CYP3A inducers (e.g., rifampin)

Patents

Primary sources

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