AIMS: The study aimed to investigate the clinical adherence to drug label 
recommendations on important drug-drug interactions (DDIs). Dispensing data on 
drug combinations involving selective serotonin reuptake inhibitor (SSRI) 
antidepressants could help to identify areas for intensified medical education.
METHODS: This was a retrospective, cross-sectional analysis of individual 
dispensing data regarding all individuals > or =15 years old in Sweden. The 
study analysed the prescribing and dispensing of CYP2D6 drugs (metoprolol, 
donepezil, galantamine, codeine, tamoxifen) together with CYP2D6-blocking SSRIs 
(paroxetine/fluoxetine) or SSRIs without significant CYP2D6 inhibition 
(citalopram/escitalopram/sertraline), and the related prescribing of 
CYP2D6-independent comparator drugs (atenolol, rivastigmine, propoxyphene, 
anastrozole). Odds were calculated between each CYP2D6 drug and the 
corresponding comparator drug in patients on fluoxetine/paroxetine and 
citalopram/escitalopram/sertraline, respectively. The odds ratio (OR) was 
calculated by dividing the obtained odds in patients on fluoxetine/paroxetine by 
the corresponding odds in patients on citalopram/escitalopram/sertraline.
RESULTS: Compared with patients that were dispensed 
citalopram/escitalopram/sertraline, patients dispensed fluoxetine/paroxetine had 
lower prescribing rates of metoprolol (adjusted OR 0.80; 95% confidence interval 
0.76, 0.85), donepezil (0.65; 0.49, 0.86) and galantamine (0.58; 0.41, 0.81). In 
contrast, the use of prodrugs codeine (compared woth propoxyphene) or tamoxifen 
(compared with anastrozole) was similar among patients on fluoxetine/paroxetine 
and citalopram/escitalopram/sertraline (adjusted OR 1.03; 0.94, 1.12 and 1.29; 
0.96, 1.73, respectively).
CONCLUSIONS: Clinically important DDIs that are associated with impaired 
bioactivation of prodrugs might be more easily neglected in clinical practice 
compared with DDIs that cause drug accumulation and symptomatic adverse drug 
reactions.