Atomoxetine and Duloxetine: Evaluation of a Potential Pharmacokinetic Drug-Drug Interaction

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Objective: The present research aimed to investigate whether a pharmacokinetic drug interaction exists between atomoxetine, a substrate of CYP2D6 and duloxetine, an enzymatic inhibitor of the same metabolic pathway.

Methods: Twenty-three healthy volunteers were enrolled in an open-label, non-randomized, sequential, 2-period clinical study. During the trial, they received a single dose of atomoxetine 25 mg (Period 1:Reference) followed by a combination of atomoxetine 25 mg and duloxetine 30 mg, after a pretreatment regimen with duloxetine 30-60 mg/day for 4 days (Period 2:Test). The pharmacokinetic parameters of atomoxetine and its main metabolite (4-hydroxyatomoxetine-O-glucuronide) were estimated using a non-compartmental approach and statistical tests were used to compare these parameters between study periods.

Results: A total of 22 subjects, extensive metabolizers (EMs), were considered for the final report of the study findings. Duloxetine influenced the plasma concentration-time profile of both parent drug and its glucuronidated metabolite. The pharmacokinetic and statistical analysis revealed that pretreatment with the enzymatic inhibitor increased the mean atomoxetine AUC0–t (from 1151.19±686.52 to 1495.54±812.40 [ng*h/mL]) and AUC0–∞ (from 1229.15±751.04 to 1619.37±955.01 [ng*h/mL]) while kel was decreased and the mean t1/2 was prolonged. With regard to 4-hydroxyatomoxetine-O-glucuronide, Cmax was reduced from 688.76±270.27 to 621.60±248.82 [ng/mL] after coadministration of atomoxetine and duloxetine.

Conclusions: Duloxetine had an impact on the pharmacokinetics of atomoxetine as it increased the exposure to the latter by ~30%. Although the magnitude of this pharmacokinetic interaction is rather small, a potential clinical relevance cannot be ruled out with certainty without further investigation.

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