Gradual increase of avacopan dose with concomitant ursodeoxycholic acid use may help avoid the risk of C5a receptor inhibitor-induced liver injury in antineutrophil cytoplasmic antibody-associated vasculitis.

Microscopic polyangiitis is a necrotising vasculitis characterised by anti-neutrophil cytoplasmic antibodies against myeloperoxidase. The complement component 5a receptor inhibitor avacopan effectively sustains remission in microscopic polyangiitis with a reduction in prednisolone dosage. Liver damage is a safety concern for this drug. However, when it occurs and how to treat it remain unknown. A 75-year-old man developed microscopic polyangiitis and presented with hearing impairment and proteinuria. Methylprednisolone pulse therapy followed by 30 mg/day prednisolone and two doses of weekly rituximab were administered. Avacopan was initiated to taper prednisolone for sustained remission. After 9 weeks, liver dysfunction and sparse skin eruptions developed. The cessation of avacopan and the initiation of ursodeoxycholic acid improved liver function without discontinuation of prednisolone and other concomitant drugs. After 3 weeks, avacopan was rechallenged with a small dose that was gradually increased; ursodeoxycholic acid was continued. Full-dose avacopan did not induce recurrence of liver injury. Therefore, gradually increasing the dose of avacopan with concomitant ursodeoxycholic acid use may help avoid possible avacopan-induced liver injury.