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.