SHR6390 is an oral, potent and selective small-molecule CDK4/6 inhibitor for the treatment of human breast, ovarian and colon cancer. Previous studies have shown that SHR6390 in combination with rifampicin, a potent inducer of CYP3A4, significantly reduces exposure levels. Therefore, we further investigated the effect of efavirenz, a moderate CYP3A4 inducer, on a single oral dose of SHR6390 in healthy volunteers.Twenty healthy subjects were enrolled in this single-center, open, single-dose, self-controlled DDI study. On Day 1, subjects received a single oral dose of 150mg SHR6390; on Day 8-26, subjects received 600 mg efavirenz orally at night, with a single dose of 150 mg SHR6390 on Day 22. Blood samples for pharmacokinetic analyses were collected.The geometric mean ratios of the maximum concentration(Cmax) and the area under the concentration curve from zero to infinity (AUC0-inf) between combination therapy and SHR6390 monotherapy (combination therapy/SHR6390 monotherapy) and their 90% confidence intervals were 0.562 (0.482, 0.654) and 0.328 (0.278, 0.386), respectively. This indicates that the Cmax and AUC0 inf of SHR6390 decreased by approximately 43.8% and 67.2%, respectively. Oral administration of 150 mg SHR6390 alone or together with efavirenz was safe and tolerable in healthy subjects.It is suggested that under the action of the moderate CPY3A4 inducer efavirenz, the exposure AUC of SHR6390 exhibits a moderate level of induction. It is recommended to avoid concomitant administration of moderate inducers of CYP3A4 during treatment with SHR6390.http://www.chinadrugtrials.org.cn/index.html, CTR20211571/ https://classic.clinicaltrials.gov, NCT04973020.© 2024 Wang et al.