The Possibility of Therapeutic Drug Monitoring of the Most Important 
Interactions in Nursing Homes

BACKGROUND: Therapeutic drug monitoring is a relevant tool in drug treatment of elderly patients. The aim of this study was to assess the possibility of therapeutic drug monitoring of the most important potential interactions in nursing homes. METHODS: A material of prescribed drugs to 446 patients in three nursing homes in Bergen, Norway from a single day in March 2016 was analysed. Clinically relevant drug interactions (pharmacodynamic or pharmacokinetic) were identified and classified with Stockley`s Interaction Alerts. The most important interaction among several in each patient were ranked by recommended action > severity > evidence according to Stockley`s. The possibility of therapeutic drug monitoring of drug combinations involved in the most important interactions was retrieved from a database of all laboratories performing clinical pharmacology in Norway (the Pharmacology Portal). RESULTS: Two or more drugs were used by 443 (99.3%) of 446 patients. Three-hundred and eighty-four patients (86.1%) had > 1 interaction. About 95% of the most important interactions were pharmacodynamic. In 280 (72.9%) of these interactions, Stockley`s recommended adjust dose or monitoring. Among the 384 most important interactions, 93% involved one drug and 41% involved two drugs available for therapeutic drug monitoring. CONCLUSION: In this pilot study, therapeutic drug monitoring was possible in the majority of the most important interactions in Norwegian nursing homes. This option is of importance since adjust dose or monitoring were frequently recommended actions associated with these interactions.