title: Co-Prescribing of Potentially Interacting Drugs during Warfarin Therapy - A Population-Based Register Study.
abstract: We analysed the occurrence of co-prescribing of potentially interacting drugs during warfarin therapy in the community-dwelling population of Finland. We identified drugs having interaction potential with warfarin using the Swedish Finnish INteraction X-referencing drug-drug interaction database (SFINX) and obtained data on drug purchases from the nationwide Prescription Register. We defined warfarin users as persons purchasing warfarin in 2010 (n = 148,536) and followed them from their first prescription in 2010 until the end of the calendar year. Co-prescribing was defined as at least 1-day overlap between warfarin and interacting drug episodes. In addition, we identified persons who initiated warfarin therapy between 1 January 2007 and 30 September 2010 (n = 110,299) and followed these incident users for a 3-month period since warfarin initiation. Overall, 74.4% of warfarin users were co-prescribed interacting drugs. Co-prescribing covered 46.4% of the total person-years of warfarin exposure. Interacting drugs that should be avoided with warfarin were co-prescribed for 13.4% of warfarin users. The majority of the co-prescriptions were for drugs that are not contraindicated during warfarin therapy but require special consideration. Among incident users, 57.1% purchased potentially interacting drugs during the 3-month period after initiation, while 9.0% purchased interacting drugs that should be avoided with warfarin. To conclude, the occurrence of co-prescribing of potentially interacting drugs was high during warfarin therapy. Our findings highlight the importance of close monitoring of warfarin therapy and the need for further studies on the clinical consequences of co-prescribing of interacting drugs with warfarin.
authors.affiliation: Department of Pharmacology, Drug Development and Therapeutics, University of Turku, Turku, Finland.
authors.forename: Maria
authors.initials: M
authors.lastname: Rikala
authors.affiliation: Department of Pharmacology, Drug Development and Therapeutics, University of Turku, Turku, Finland.|Unit of Clinical Pharmacology, Turku University Hospital, Turku, Finland.
authors.forename: Milka
authors.initials: M
authors.lastname: Hauta-Aho
authors.affiliation: Department of Pharmacology, Drug Development and Therapeutics, University of Turku, Turku, Finland.|Unit of Primary Health Care, Hospital District of Helsinki and Uusimaa, Helsinki, Finland.
authors.forename: Arja
authors.initials: A
authors.lastname: Helin-Salmivaara
authors.affiliation: Coagulation Disorders Unit, Hematology, Cancer Center and Laboratory Services HUSLAB, Helsinki University Central Hospital, Helsinki, Finland.
authors.forename: Riitta
authors.initials: R
authors.lastname: Lassila
authors.affiliation: Department of Pharmacology, Drug Development and Therapeutics, University of Turku, Turku, Finland.|Department of Public Health, University of Turku, Turku, Finland.
authors.forename: Maarit Jaana
authors.initials: MJ
authors.lastname: Korhonen
authors.affiliation: Department of Pharmacology, Drug Development and Therapeutics, University of Turku, Turku, Finland.|Unit of Clinical Pharmacology, Turku University Hospital, Turku, Finland.
authors.forename: Risto
authors.initials: R
authors.lastname: Huupponen
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000925:Anticoagulants / Q000008:administration & dosage* / Q000009:adverse effects; D016208:Databases, Factual; D004347:Drug Interactions; D016903:Drug Monitoring / Q000379:methods; D005260:Female; D005387:Finland; D006801:Humans; D008297:Male; D008875:Middle Aged; D010818:Practice Patterns, Physicians' / Q000592:standards / Q000706:statistics & numerical data*; D055553:Prescription Drugs / Q000008:administration & dosage* / Q000009:adverse effects; D012042:Registries; D014859:Warfarin / Q000008:administration & dosage* / Q000009:adverse effects
chemical_list: D000925:Anticoagulants; D055553:Prescription Drugs; D014859:Warfarin