Objective: To determine the prevalence of the potential interactions attributed to concomitant use of fluoxetine (FLX) with other therapeutic agents commonly prescribed at Songkhla Rajanagarindra Hospital.

Method: Outpatient prescription data (June-August 2006) were retrospectively collected and analyzed. Information including patient's characteristics, number of events which FLX was co-prescribed with other drugs, dose and dosage regimen of FLX and those of the co-prescribed agents which can cause drug interactions (DIs) were recorded. The prevalence of potential DIs was reported as percentage and classified according to patient's age, gender, and significance level.

Results: Sixty percent of 1,539 prescriptions containing FLX were likely to cause DIs. Thisnumber corresponded to 1,176 out of 1,802 pairs of FLX co-prescriptions. Dose of 20 mg/day was mostly prescribed for FLX, and patients aged 20-40 years old were mostly receiving FLX co prescription. Significance level 4 interactions were mostly characterized (45.2% of the potential DIs). Among the total of 15 drugs potentially causing DI with FLX, propranolol was the most frequently co-prescribed agent. Other agents found to be frequently co-prescribed with FLX were haloperidol, clozapine, tricyclic antidepressants, and anticonvulsants.

Conclusion: Sixty percent of FLX co-prescription was likely to cause DI at Songkhla Rajanagarindra Hospital. Among the 15 identified agents potentially causing DI, frequently co-prescribed agents with FLX were propranolol, haloperidol, and clozapine.