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It was determined through genetic testing that he is an intermediate metaboliser of CYP2D6, the main enzyme contributing to the metabolism of timolol. This explains the development of the bradycardia after intranasal timolol use. The metabolising variants of CYP2D6 need to be considered when prescribing medications metabolised by this enzyme, so possible adverse effects can be avoided.<\/jats:p>","DOI":"10.1136\/bcr-2013-203056","type":"journal-article","created":{"date-parts":[[2014,2,11]],"date-time":"2014-02-11T05:19:35Z","timestamp":1392095975000},"page":"bcr2013203056","update-policy":"https:\/\/doi.org\/10.1136\/crossmarkpolicy","source":"Crossref","is-referenced-by-count":13,"title":["Topical timolol for treatment of epistaxis in hereditary haemorrhagic telangiectasia associated with bradycardia: a look at CYP2D6 metabolising variants"],"prefix":"10.1136","volume":"2014","author":[{"given":"Narendranath","family":"Epperla","sequence":"first","affiliation":[{"name":"Department of Internal Medicine and Clinical Research, Marshfield Clinic, Marshfield, Wisconsin, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Murray 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