TEGSEDI causes reductions in platelet count at any time during treatment that may result in sudden and unpredictable thrombocytopenia that can be life-threatening. In Study 1 [see Clinical studies (14)] , platelet counts below 100 x 109/L occurred in 25% of TEGSEDI-treated patients, compared with 2% of patients on placebo. Platelet counts below 75 x 109/L occurred in 14% of TEGSEDI-treated patients, compared to no patient on placebo. In Study 1 and its extension study, 39% of TEGSEDI-treated patients with a baseline platelet count below 200 x109/L had a nadir platelet count below 75 x 109/L, compared to 6% of patients with baseline platelet counts 200 x109/L or higher.

Three TEGSEDI-treated patients (3%) had sudden severe thrombocytopenia (platelet count below 25 x 109/L), which can have potentially fatal bleeding complications, including spontaneous intracranial or intrapulmonary hemorrhage. One patient in a clinical trial experienced a fatal intracranial hemorrhage.

In clinical trials, all 3 patients with severe thrombocytopenia had treatment-emergent antiplatelet IgG antibodies detected shortly before or at the time of the severe thrombocytopenia. In 2 patients, platelet clumping caused uninterpretable platelet measurements that delayed the diagnosis and treatment of severe thrombocytopenia. Platelet clumping can be caused by a reaction between antiplatelet antibodies and ethylenediaminetetraacetic acid (EDTA) [see Warnings and Precautions (5.8)]. 

Monitoring and Dosing

Patients who are not able to adhere to the recommended laboratory monitoring or to the related treatment recommendations must not receive TEGSEDI. Do not initiate TEGSEDI in patients with a platelet count below 100 x 109/L. Follow recommended monitoring and treatment recommendations for platelet count [see Dosage and Administration (2.4)]. If a patient develops signs or symptoms of thrombocytopenia, obtain a platelet count as soon as possible, and hold TEGSEDI dosing unless the platelet count is confirmed to be acceptable. Recheck the platelet count as soon as possible if a platelet measurement is uninterpretable (e.g., clumped sample) [see Warnings and Precautions (5.8)]. Hold TEGSEDI dosing until an acceptable platelet count is confirmed with an interpretable blood sample.

Concomitant Medications with Platelet Effects

When considering use of TEGSEDI concomitantly with antiplatelet drugs or anticoagulants, be aware of the risk of potential bleeding from thrombocytopenia with TEGSEDI, and consider discontinuation of these drugs in patients with a platelet count less than 50 x 109/L [see Drug Interactions (7.1)]. 

Symptoms of Thrombocytopenia

Symptoms of thrombocytopenia can include unusual or prolonged bleeding (e.g., petechiae, easy bruising, hematoma, subconjunctival bleeding, gingival bleeding, epistaxis, hemoptysis, irregular or heavier than normal menstrual bleeding, hematemesis, hematuria, hematochezia, melena), neck stiffness or atypical severe headache. Patients and caregivers should be instructed to be vigilant for symptoms of thrombocytopenia and seek immediate medical help if they have concerns.

Severe Thrombocytopenia: Treatment with Glucocorticoids

Glucocorticoid therapy is strongly recommended in patients with a platelet count below 50 x 109/L, and in patients with suspected immune-mediated thrombocytopenia. Avoid using TEGSEDI in patients for whom glucocorticoid treatment is not advised.