GC376 is an inhibitor of 3C-like proteases (3CLpro) with IC50 values range from 0.49~4.35 μM.

3CLpro:0.49~4.35 μM.

GC376对冠状病毒（TGEV、FIPV、MHV、229E和BCV）、卡利西病毒（NV和MNV-1）以及皮克纳病毒（HRVs 18、51和68、EV71和PTV）表现出显著的抑制效果，IC50值达到纳摩尔或低微摩尔水平，除了FCV和HAV外。有趣的是，FCV对GC376的敏感性较低，其IC50值为35 μM [1]。

GC376以15 mg/kg的剂量，每12小时通过皮下注射给药。结果表明，在初始治疗后的2周内，20只接受GC376治疗的猫中有19只恢复了正常健康状况。然而，疾病迹象在初次治疗后1-7周内复发，复发和新发病例最终需要至少治疗12周。在初次或重复治疗后的1-7周内，13只中的19只猫发生了不再对治疗有反应的复发 [2]。

The toxic dose for 50% cell death (TD50) for each compound was determined for the various cells used in this study. Confluent cells grown in 96-well plates were treated with various concentrations (1 to 500 μM) of each compound for 72 h. Cell cytotoxicity was measured by a CytoTox 96 nonradioactive cytotoxicity assay kit and crystal violet staining. The in vitro therapeutic index was calculated by dividing the TD50 by the IC50 [1].

GC376 was synthesized in a highly pure form and formulated at a concentration of 53 mg/ml in 10% ethanol and 90% polyethylene glycol 400, as described previously. GC376 was administered subcutaneously (SC) at a dosage of 15 mg/kg q12h SC, unless stated otherwise. The effective dosage for cats with experimentally induced FIP was 10 mg/kg/ q12h SC, but the dosage was raised to 15 mg/kg after the first cat (CT01) failed to respond to a lower dose of 10 mg/kg suggested by earlier pharmacokinetic studies. This was a clinical decision based on this one cat's response to treatment [2].