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 eightyfour
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.