Sotatercept

12.1 Mechanism of Action Sotatercept-csrk, a recombinant activin receptor type IIA-Fc (ActRIIA-Fc) fusion protein, is an activin signaling inhibitor that binds to activin A and other TGF- β superfamily ligands. As a result, sotatercept-csrk improves the balance between the pro-proliferative (ActRIIA/Smad2/3-mediated) and anti-proliferative (BMPRII/Smad1/5/8-mediated) signaling to modulate vascular proliferation. In rat models of PAH, a sotatercept-csrk analog reduced inflammation and inhibited proliferation of endothelial and smooth muscle cells in diseased vasculature. These cellular changes were associated with thinner vessel walls, partial reversal of right ventricular remodeling, and improved hemodynamics.

1 INDICATIONS AND USAGE WINREVAIR™ is indicated for the treatment of adults with pulmonary arterial hypertension (PAH, Group 1 pulmonary hypertension) to improve exercise capacity and World Health Organization (WHO) functional class (FC), and reduce the risk of clinical worsening events including hospitalization for PAH, lung transplantation and death [see Clinical Studies (14.1) ] . WINREVAIR is an activin signaling inhibitor indicated for the treatment of adults with pulmonary arterial hypertension (PAH, WHO Group 1 pulmonary hypertension) to improve exercise capacity and WHO functional class (FC), and reduce the risk of clinical worsening events, including hospitalization for PAH, lung transplantation and death. ( 1 )

2 DOSAGE AND ADMINISTRATION The recommended starting dose is 0.3 mg/kg by subcutaneous injection. ( 2.1 ) The recommended target dose is 0.7 mg/kg every 3 weeks by subcutaneous injection. ( 2.2 ) Dosage modifications due to increased hemoglobin (Hgb) and decreased platelets may be necessary. Check Hgb and platelets before each dose for the first 5 doses, or longer if values are unstable, and monitor periodically thereafter. ( 2.3 ) See full prescribing information for preparation and administration instructions. ( 2.4 ) 2.1 Recommended Starting Dosage WINREVAIR is administered once every 3 weeks by subcutaneous injection according to patient body weight. The starting dose of WINREVAIR is 0.3 mg/kg. Obtain hemoglobin (Hgb) and platelet count prior to the first dose of WINREVAIR. Do not initiate treatment if platelet count is <50,000/mm 3 (<50 x 10 9 /L) [see Dosage and Administration (2.3) ] . Injection volume for starting dose is calculated based on patient weight as follows: Injection Volume (mL) = Weight (kg) x 0.3 mg/kg 50 mg/mL Injection volume should be rounded to the nearest 0.1 mL. For example: (70 kg x 0.3 mg/kg) ÷ 50 mg/mL = 0.42 mL, rounds to 0.4 mL See Table 1 for selecting the appropriate kit based on calculated injection volume for starting dose. Table 1: Kit Type Based on Injection Volume for Dose of 0.3 mg/kg Injection Volume (mL) Kit Type 0.2 to 0.9 45 mg kit (containing 1 x 45 mg vial) 1 to 1.1 60 mg kit (containing 1 x 60 mg vial) 2.2 Recommended Target Dosage After verifying acceptable Hgb and platelet count, increase to the target dose of 0.7 mg/kg. Continue treatment at 0.7 mg/kg every 3 weeks unless dosage adjustments are required [see Dosage and Administration (2.3) ] . Injection volume for target dose is calculated based on patient weight as follows: Injection Volume (mL) = Weight (kg) x 0.7 mg/kg 50 mg/mL Injection volume should be rounded to the nearest 0.1 mL. For example: (70 kg x 0.7 mg/kg) ÷ 50 mg/mL = 0.98 mL, rounds to 1 mL See Table 2 for selecting the appropriate kit based on calculated injection volume for target dose. Table 2: Kit Type Based on Injection Volume for Dose of 0.7 mg/kg Injection Volume (mL) Kit Type 0.4 to 0.9 45 mg kit (containing 1 x 45 mg vial) 1 to 1.2 60 mg kit (containing 1 x 60 mg vial) 1.3 to 1.8 90 mg kit (containing 2 x 45 mg vials) 1.9 to 2.4 120 mg kit (containing 2 x 60 mg vials) Missed Dose, Overdose, and Underdose If a dose of WINREVAIR is missed, administer as soon as possible. If the missed dose of WINREVAIR is not administered within 3 days of the scheduled date, adjust the schedule to maintain 3-week dosing intervals. In case of an overdose, monitor for erythrocytosis [see Overdosage (10) ] . 2.3 Dosage Modifications Due to Hemoglobin Increase or Platelet Count Decrease Check Hgb and platelet count before each dose for the first 5 doses, or longer if values are unstable. Thereafter, monitor Hgb and platelet count periodically [see Warnings and Precautions (5.1 , 5.2) ] . Delay treatment for at least 3 weeks if any of the following occur: Hgb increases >2.0 g/dL from the previous dose and is above ULN. Hgb increases >4.0 g/dL from baseline. Hgb increases >2.0 g/dL above ULN. Platelet count decreases to <50,000/mm 3 (<50 x 10 9 /L). Recheck Hgb and platelet count before reinitiating treatment. For treatment delays lasting >9 weeks, restart treatment at 0.3 mg/kg, and escalate to 0.7 mg/kg after verifying acceptable Hgb and platelet count. 2.4 Preparation and Administration Administration is subject to monitoring of hemoglobin and platelet count [see Dosage and Administration (2.3) , Warnings and Precautions (5.1 , 5.2) ] . WINREVAIR is intended for use under the guidance of a healthcare professional. Patients and caregivers may administer WINREVAIR when considered appropriate and when they receive training and follow-up from the healthcare provider (HCP) on how to reconstitute, prepare, measure, and inject WINREVAIR [see Patient Counseling Information (17) ] . Confirm at subsequent visits that the patient and/or caregiver can correctly prepare and administer WINREVAIR, particularly if the dose changes or the patient requires a different kit [see Warnings and Precautions (5.1) ] . Refer to the Instructions for Use (IFU) for detailed instructions on the proper preparation and administration of WINREVAIR. Selecting the Appropriate Product Kit If a patient’s body weight requires the use of two 45 mg vials or two 60 mg vials of lyophilized product, use a 2-vial kit instead of two individual 1-vial kits. A 2-vial kit includes instructions to combine the contents of two vials, which aids in measuring the proper dosage and eliminates the need for multiple injections [see How Supplied/Storage and Handling (16.1) ] . Reconstitution Instructions Remove the injection kit from the refrigerator and wait 15 minutes to allow the prefilled syringe(s) and drug product to come to room temperature prior to preparation. Attach the vial adapter to the vial. Visua

6 ADVERSE REACTIONS The following clinically significant adverse reactions are described elsewhere in the labeling: Erythrocytosis [see Warnings and Precautions (5.1) ] Severe Thrombocytopenia [see Warnings and Precautions (5.2) ] Serious Bleeding [see Warnings and Precautions (5.3) ] Embryo-Fetal Toxicity [see Warnings and Precautions (5.4) ] Impaired Fertility [see Warnings and Precautions (5.5) ] The most common (≥10% in patients receiving WINREVAIR and 5% more than placebo) adverse reactions were infections, epistaxis, telangiectasia, diarrhea, headache, rash, increased hemoglobin, dizziness, erythema, and gingival bleeding. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Merck Sharp & Dohme LLC at 1-877-888-4231 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch 6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. STELLAR The following data reflect exposure to WINREVAIR in the STELLAR trial. Adult PAH patients with WHO FC II or III (n=323) were randomized in a 1:1 ratio to receive WINREVAIR or placebo in combination with background standard of care therapies. Patients received a starting dose of 0.3 mg/kg via SC injection and the dose was increased to the target dose of 0.7 mg/kg administered once every 3 weeks for 24 weeks. After completing the primary 24-week treatment phase, patients continued into a long-term double-blind (LTDB) treatment period, maintaining their randomized treatment assignment, until all patients completed the primary treatment period. The median duration of treatment was 273 days in the placebo group and 313 days in the WINREVAIR group [see Clinical Studies (14.1) ]. The most common adverse reactions occurring in STELLAR (≥10% for WINREVAIR and at least 5% more than placebo) are shown in Table 3 . Table 3: Adverse Reactions ≥10% in Patients Receiving WINREVAIR and at least 5% More Than Placebo in STELLAR Double-blind placebo-controlled period + Long-term double-blind period of STELLAR Adverse reaction WINREVAIR N=163 Placebo N=160 Headache 40 (24.5) 28 (17.5) Epistaxis 36 (22.1) 3 (1.9) Rash 33 (20.2) 13 (8.1) Telangiectasia 27 (16.6) 7 (4.4) Diarrhea 25 (15.3) 16 (10.0) Dizziness 24 (14.7) 10 (6.3) Erythema 22 (13.5) 5 (3.1) Increased Hemoglobin Increases in Hgb were managed by dose delays (10%), dose reductions (6%), or both (5%). Shifts in Hgb from normal to above normal levels occurred in 87 (53%) patients receiving WINREVAIR and in 23 (14%) patients receiving placebo. Thrombocytopenia Decreases in platelets were managed by dose delays (2%), dose reductions (2%), or both (2%). Shifts in platelet count from normal to below normal occurred in 40 (25%) patients receiving WINREVAIR and in 26 (16%) patients receiving placebo. Telangiectasia In patients exposed to WINREVAIR who experienced telangiectasia, the median time to onset was 36.1 weeks. Increased Blood Pressure In patients taking WINREVAIR, mean systolic/diastolic blood pressure increased from baseline by 2.2/4.9 mmHg at 24 weeks. In patients taking placebo, the change from baseline in mean blood pressure was -1.6/-0.6 mmHg. Treatment Discontinuation The incidences of treatment discontinuations due to an adverse reaction were 4% in the WINREVAIR group and 7% in the placebo group. No specific adverse reactions causing treatment discontinuations occurred with a frequency greater than 1% and more often in the WINREVAIR group. ZENITH The following data reflect exposure to WINREVAIR in the ZENITH trial. Adult PAH patients with WHO FC III or IV at high risk of mortality (n=172) were randomized in a 1:1 ratio to treatment with WINREVAIR or placebo in combination with background standard of care therapies. Patients who did not experience a primary endpoint event remained in the Double-Blind Placebo-Controlled (DBPC) Treatment Period, while patients who experienced an event of PAH worsening-related hospitalization of ≥24 hours were eligible to enroll into the open-label, long-term follow-up (LTFU) study SOTERIA. The median duration of exposure was longer in the WINREVAIR group (435 days) than in the placebo group (268 days) [see Clinical Studies (14.1) ]. The overall incidences of adverse reactions in both arms were higher in the ZENITH trial than in the STELLAR trial. Severe reduction in platelet count <50,000/mm 3 (<50.0 x 10 9 /L) occurred in 6% of patients taking WINREVAIR. In the WINREVAIR group, 1 patient (1%) discontinued study intervention due to an adverse event, compared with 4 patients (5%) in the placebo group. Table 4: Adverse Reactions ≥10% in Patients Receiving WINREVAIR and at least 5% More Than Placebo in ZENITH Adverse reaction WINREVAIR N=86 Placebo N=86 Infections 58 (67.4) 38 (44.2) Epistaxis 39 (45.3) 8 (9.3) Diarrhea 22 (25.6) 15 (17.4) Telangiectasia 22 (25.6) 3 (3