A patient with microscopic polyangiitis (MPA)—a form of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV)—being treated with avacopan developed thrombocytopenia, researchers reported in the International Journal of Rheumatic Diseases.

AAV, which comprises a group of debilitating autoimmune disorders, can affect the small vessels of the lungs, kidneys, and neurologic system. AAV includes both MPA and granulomatosis with polyangiitis (GPA). Immunosuppressant therapy has been linked to major improvements in the prognosis of patients with AAV

The novel C5a receptor antagonist avacopan was recently approved in the United States and Japan for the treatment of MPA and GPA. It works by blocking the binding of C5a to its receptor, as well as neutrophil activation and recruitment, thus potentially mitigating vascular inflammation.

The current case report describes the first time that avacopan-induced thrombocytopenia has been reported in a patient treated with the agent. The patient was a 78-year-old Japanese man with a recent history of rapidly progressive glomerulonephritis (RPGN) and vasculitis neuropathy linked to MPA. He was admitted to the hospital for the development of severe anemia. He had been diagnosed with immunoglobulin A nephropathy 13 years prior to the current episode.

Learn more about ANCA-associated vasculitis

The patient received prednisolone for the treatment of his RPGN, which proved ineffective. With the weaning of his corticosteroid dosage, he developed impaired dorsiflexion of his left ankle, along with numbness and tingling in his feet—both of which are consistent with vascular neuropathy.

Following 3 days of methylprednisolone therapy, avacopan and prednisolone 20 mg/day were administered in an effort to decrease the steroid dosage. One week following the initiation of avacopan, the patient’s platelet counts began to decline, which eventually necessitated discontinuation of the therapy.

Heparin-induced thrombocytopenia and thrombotic microangiopathy were both considered unlikely causes of his anemia, based on the patient’s clinical disease course and laboratory tests. Following avacopan withdrawal for 3 weeks, his platelet counts began to rise, thus implying that avacopan was the most likely causative agent.

It is well recognized that the diagnosis of drug-induced thrombocytopenia presents a challenge, which is due, in part, to the lack of a standardized reliable test for confirmation of the condition. “As such, clinicians usually need to rely on clinical judgment by evaluating the platelet count trajectory before and after the use of the responsible drug, as was the case with our patient,” the researchers wrote.

“Our case highlights the importance of postmarketing surveillance of avacopan to identify [any] adverse events that were not reported in clinical trials,“ they added. Clinicians should carefully monitor platelet counts when using avacopan.”


Morimoto N, Mori T, Shioji S, et al. Thrombocytopenia during avacopan administration: a case report. Int J Rheum Dis. Published online March 7, 2023. doi:10.1111/1756-185X.14645