{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,6]],"date-time":"2026-09-06T04:10:59Z","timestamp":1788667859643,"version":"build-2803163510"},"reference-count":28,"publisher":"SAGE Publications","license":[{"start":{"date-parts":[[2026,9,4]],"date-time":"2026-09-04T00:00:00Z","timestamp":1788480000000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/journals.sagepub.com\/page\/policies\/text-and-data-mining-license"}],"content-domain":{"domain":["journals.sagepub.com"],"crossmark-restriction":true},"short-container-title":["J Oncol Pharm Pract"],"abstract":"<jats:sec>\n                    <jats:title>Background<\/jats:title>\n                    <jats:p>Ribociclib, a cyclin-dependent kinase (CDK) 4\/6 inhibitor used in metastatic breast cancer, is a time-dependent inhibitor of cytochrome P450 (CYP) 3A4. While interactions with direct oral anticoagulants (DOACs) are recognized, interactions with warfarin may be underrecognized.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Case Presentation<\/jats:title>\n                    <jats:p>A woman in her late 70's taking warfarin for atrial fibrillation developed a critically elevated international normalized ratio (INR) of 16.4 and epistaxis approximately 2 weeks after initiation of ribociclib for breast cancer. She had been transitioned from apixaban to warfarin approximately 2 months earlier due to concern for a potential interaction between apixaban and ribociclib. Her INR had remained stable prior to ribociclib initiation, with a time in therapeutic range (TTR) of 78%.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Management and Outcome<\/jats:title>\n                    <jats:p>The patient required reversal with vitamin K and 4-factor prothrombin complex concentrate (4F-PCC). Ribociclib-associated CYP3A4 inhibition was considered the most plausible contributing factor to the critically elevated INR. Warfarin was resumed at a reduced dose with close outpatient monitoring.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Discussion<\/jats:title>\n                    <jats:p>This case highlights the risk of a clinically significant anticoagulant interaction following ribociclib initiation. Although warfarin allows monitoring via INR, insufficient early monitoring may increase patient risk. Weekly INR monitoring during the first 2 cycles of ribociclib may improve safety.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1177\/10781552261483495","type":"journal-article","created":{"date-parts":[[2026,9,4]],"date-time":"2026-09-04T15:55:05Z","timestamp":1788537305000},"update-policy":"https:\/\/doi.org\/10.1177\/sage-journals-update-policy","source":"Crossref","is-referenced-by-count":0,"title":["Severe Supratherapeutic international normalized ratio (INR) following concomitant Ribociclib and warfarin therapy"],"prefix":"10.1177","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-2601-7260","authenticated-orcid":false,"given":"Melanie","family":"Maine-Timbs","sequence":"first","affiliation":[{"name":"Baylor, Scott & White Hospital"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"179","published-online":{"date-parts":[[2026,9,4]]},"reference":[{"key":"e_1_3_2_2_2","unstructured":"Novartis Pharmaceuticals Corporation. Kisqali (Ribociclib) package insert. 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