Mouse, rat, and dog bioavailability and mouse oral antidepressant efficacy of ()-hydroxynorketamine.

BACKGROUND

()-ketamine has gained attention for its rapid-acting antidepressant actions in patients with treatment-resistant depression. However, widespread use of ketamine is limited by its side effects, abuse potential, and poor oral bioavailability. The ketamine metabolite, ()-hydroxynorketamine, exerts rapid antidepressant effects, without ketamine's adverse effects and abuse potential, in rodents.

METHODS

We evaluated the oral bioavailability of ()-hydroxynorketamine in three species (mice, rats, and dogs) and also evaluated five candidate prodrug modifications for their capacity to enhance the oral bioavailability of ()-hydroxynorketamine in mice. Oral administration of ()-hydroxynorketamine was assessed for adverse behavioral effects and for antidepressant efficacy in the mouse forced-swim and learned helplessness tests.

RESULTS

()-hydroxynorketamine had absolute bioavailability between 46-52% in mice, 42% in rats, and 58% in dogs. Compared to intraperitoneal injection in mice, the relative oral bioavailability of ()-hydroxynorketamine was 62%, which was not improved by any of the candidate prodrugs tested. Following oral administration, ()-hydroxynorketamine readily penetrated the brain, with brain to plasma ratios between 0.67-1.2 in mice and rats. Oral administration of ()-hydroxynorketamine to mice did not alter locomotor activity or precipitate behaviors associated with discomfort, sickness, or stereotypy up to a dose of 450 mg/kg. Oral ()-hydroxynorketamine reduced forced-swim test immobility time (15-150 mg/kg) and reversed learned helplessness (50-150 mg/kg) in mice.

CONCLUSIONS

These results demonstrate that ()-hydroxynorketamine has favorable oral bioavailability in three species and exhibits antidepressant efficacy following oral administration in mice.