Potential interactions of methylphenidate and atomoxetine with dextromethorphan.

Objective: To examine the potential for drug-drug interactions to influence drug metabolism between the attention-deficit/hyperactivity disorder (ADHD) dl-methylphenidate and atomoxetine with dextromethorphan, a probe for interactions involving cytochrome P450 (CYP) 2D6 isoenzyme.

Design: In vitro and ex vivo analysis of changes in metabolism of study drugs.

Setting: Laboratory.

Synthesis and biological evaluation of the major metabolite of atomoxetine: elucidation of a partial kappa-opioid agonist effect.

The major human metabolite of atomoxetine (4-hydroxyatomoxetine) was tested against a panel of receptors and enzymes, and was found to interact with the mu, delta, and kappa-opioid receptors based upon studies involving both binding and functional assays. 4-hydroxyatomoxetine was determined to be a partial agonist of the kappa-opioid receptor.