In short
Dasatinib is a tyrosine kinase inhibitor drug approved by the FDA for treating chronic myeloid leukemia and Philadelphia-chromosome-positive acute lymphoblastic leukemia, which was separately identified as having senolytic activity when combined with the flavonoid quercetin.
As an approved cancer drug, dasatinib has an extensive safety and pharmacokinetic profile at the continuous, higher doses used in oncology, where it works by inhibiting BCR-ABL and other tyrosine kinases that drive leukemic cell proliferation — a mechanism unrelated to its senolytic use. The senolytic application uses a much lower dose, given intermittently (for example, a few consecutive days per month) rather than continuously, based on the premise that senescent cells can be selectively cleared with brief exposure while sparing the ongoing side-effect burden of continuous cancer-treatment dosing.
This intermittent, low-dose senolytic regimen is the one used in the published D+Q human pilot studies discussed under "senolytics," and is meaningfully different from dasatinib's approved oncology dosing in both dose and schedule — meaning its long-term safety profile at senolytic doses is not the same well-established body of evidence as its oncology safety data, even though both use the same drug.
Using dasatinib for senolytic purposes outside a clinical trial is an off-label use of an approved chemotherapy drug, and it carries dasatinib's known class risks — including fluid retention, bleeding risk, and QT-interval prolongation — that a prescriber would need to weigh even at lower, intermittent doses, in a context where the senolytic efficacy evidence itself remains early-stage.