Proof‐of‐concept studies demonstrated lonafarnib (LNF), a first‐in‐class oral prenylation inhibitor, efficacy in patients infected with HDV. The lonafarnib with ritonavir for HDV‐2 (LOWR‐2) study’s aim was to identify optimal combination regimens of LNF + ritonavir (RTV) ± pegylated interferon alpha (PEG‐IFNα) with efficacy and tolerability for longer‐term dosing. Here we report the safety and efficacy at end of treatment for up to 24 weeks.

Fifty‐five patients with chronic HDV were consecutively enrolled in an open‐label, single‐center, phase 2 dose‐finding study. There were three main treatment groups: high‐dose LNF (LNF ≥ 75 mg by mouth [po] twice daily [bid] + RTV) (n = 19, 12 weeks); all‐oral low‐dose LNF (LNF 25 or 50 mg po bid + RTV) (n = 24, 24 weeks), and combination low‐dose LNF with PEG‐IFNα (LNF 25 or 50 mg po bid + RTV + PEG‐IFNα) (n = 12, 24 weeks). The primary endpoint, ≥2 log₁₀ decline or < lower limit of quantification of HDV‐RNA from baseline at end of treatment, was reached in 46% (6 of 13) and 89% (8 of 9) of patients receiving the all‐oral regimen of LNF 50 mg bid + RTV, and combination regimens of LNF (25 or 50 mg bid) + RTV + PEG‐IFNα, respectively. In addition, multiple patients experienced well‐tolerated transient posttreatment alanine aminotransferase increases, resulting in HDV‐RNA negativity and alanine aminotransferase normalization. The proportions of grade 2 and 3 gastrointestinal adverse events in the high‐dose versus low‐dose groups were 49% (37 of 76) and only 22% (18 of 81), respectively.

LNF, boosted with low‐dose RTV, is a promising all‐oral therapy, and maximal efficacy is achieved with PEG‐IFNα addition. The identified optimal regimens support a phase 3 study of LNF for the treatment of HDV.