Serum Profiles of Pembrolizumab, Cardiac Troponin T, and Interleukin-6 in a Plasma Exchange–Treated Patient With Immune Checkpoint Inhibitor–Related Myocarditis

Background: A 77-year-old female patient with renal cell carcinoma, treated with intravenous pembrolizumab, developed pembrolizumab-related myocarditis accompanied by myasthenia gravis. For myasthenia gravis–related symptoms, intravenous methylprednisolone was administered on days 24–26 and 29–31 after the administration of 200 mg of pembrolizumab, and plasma exchange (PE) therapy was conducted on days 24, 26, 28, and 30. Methods: Serum pembrolizumab levels were monitored in conjunction with serum markers of myocarditis and interleukin-6 (IL-6) in the present patient treated with PE. Results: An elevated serum cardiac troponin T (cTnT) level of 0.542 ng/mL was observed 24 days after the first administration, and the serum pembrolizumab level was 15.7 µg/mL. After the first PE session, the serum levels of cTnT and IL-6 on day 25 were 0.406 ng/mL and 27.9 pg/mL, respectively, in conjunction with a decline of the serum pembrolizumab level to 4.83 µg/mL. Although the patient had a decreased serum pembrolizumab level of 3.86 µg/mL on day 29, the serum cTnT and IL-6 levels had increased to 0.843 ng/mL and 40.6 pg/mL, respectively. After the fourth PE session, serum levels of pembrolizumab, cTnT, and IL-6 on day 31 decreased to 3.62 µg/mL, 0.381 ng/mL, and 10.1 pg/mL, respectively. The overall removal rate after 4 sessions of PE was 76.9%, after which myasthenia gravis–related symptoms gradually disappeared. Conclusions: This patient with a serum pembrolizumab level within the previously reported range developed myocarditis accompanied by myasthenia gravis. PE therapy efficiently extracted circulating pembrolizumab and IL-6 in this patient with immune checkpoint inhibitor–related myocarditis.