SHR-A1811 + ritonavir

SHR-A1811 + ritonavir is an experimental **combination therapy** comprising SHR-A1811, a third-generation HER2-directed antibody-drug conjugate (ADC), and ritonavir, a known inhibitor of the cytochrome P450 3A (CYP3A) enzyme system most commonly used as a pharmacokinetic enhancer. SHR-A1811 consists of a trastuzumab backbone, a cleavable linker, and a novel topoisomerase I inhibitor payload (SHR169265), designed for potent tumor cell killing and bystander anti-tumor effect, especially in HER2-expressing cancers. Ritonavir is included here to potentially alter the pharmacokinetics of SHR-A1811 (e.g., to reduce clearance or increase exposure by inhibiting metabolism), as is being studied in drug–drug interaction trials. This combination is currently under clinical investigation for its safety and pharmacokinetics; it is not an approved therapeutic regimen. Primary indications under study for SHR-A1811 (as monotherapy and likely in this combo) include HER2-positive breast cancer, gastric cancer, colorectal cancer, and non-small cell lung cancer[1][2][3][4][5].