This is a Phase 1, 2-period, multiple-dose, open-label, single fixed sequence study of the effect of ritlecitinib on tolbutamide pharmacokinetics in healthy participants.

A total of approximately 12 healthy male and/or female participants will be enrolled in the study to obtain at least 10 evaluable participants who complete the study. This is an open-label study not requiring an assessment of efficacy or pharmacodynamics markers, but it will include pharmacokinetic estimation drug-drug interactions.

Inclusion Criteria:

• Male and/or female participants who are healthy as determined by medical evaluation including medical history, full physical examination (including BP and pulse rate measurements), clinical laboratory tests, and 12-lead ECG.
• BMI of 17.5 to 30.5 kg/m2; and a total body weight >50 kg (110 lb).

Exclusion Criteria:

• Past/present clinically significant hematological, renal, endocrine, pulmonary, GI, CV, hepatic, psychiatric, neurological, dermatological or allergic disease (including drug allergies).
• Any condition possibly affecting drug absorption (eg, gastrectomy, cholecystectomy).
• Infection with hepatitis B or C viruses.
• Participants with any of the following acute or chronic infections or infection history: any infection requiring treatment within 2 weeks prior to the start of study participation; any infection requiring hospitalization or parenteral antimicrobial therapy within 60 days of the first dose of investigational product; any infection judged to be an opportunistic infection or clinically significant within the past 6 months of the first dose of investigational product; known active or history of recurrent bacterial, viral, fungal, mycobacterial or other infections; history of recurrent localized dermatomal herpes zoster, or history of disseminated (single episode) herpes simplex or disseminated herpes zoster.
• History of any lymphoproliferative disorder such as EBV related lymphoproliferative disorder, history of lymphoma, history of leukemia, or signs or symptoms suggestive of current lymphatic or lymphoid disease.
• Known presence or a history of malignancy other than a successfully treated or excised non-metastatic basal cell or squamous cell cancer of the skin or cervical carcinoma in situ.

Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical\_trials/trial\_data\_and\_results/data\_requests.

Baseline analysis population included all participants assigned to the study intervention.

From screening up to a follow-up phone call between 28 and 35 calendar days after the last administration of the investigational product and early termination (if applicable)

The same event may appear as both an AE and a serious adverse event (SAE). An event may be categorized as serious in 1 participant and as non-serious in another participant, or 1 participant may have experienced both a serious and non-serious event during the study. Total number at risk below refers to the number of participants evaluable for SAEs or AEs.