Dihydroxyphenylglycol as a Biomarker of Norepinephrine Transporter Inhibition by Atomoxetine: Human Model to Assess Central and Peripheral Effects of Dosing.

To assess the primary metabolite of norepinephrine, 3,4-dihydroxyphenylglycol (DHPG), as a sensitive biomarker for norepinephrine transporter (NET) function and the relationship of DHPG measured peripherally and centrally, NET was antagonized with 80 mg/d atomoxetine for 18 days. Twelve healthy subjects were treated with atomoxetine in an open-label, multiple-dose exploratory study. Plasma atomoxetine reached steady state by day 6, and the pharmacokinetic results demonstrated availability of atomoxetine to the central nervous system. The cerebrospinal fluid (CSF)/plasma ratios of atomoxetine based on area under concentration-time curve from 0 to 12 hours postdose (AUC0-12), maximum concentration (Cmax), and predose were 0.3%, 0.2%, and 11%, respectively. Plasma from atomoxetine-treated subjects (ex vivo) significantly inhibited radioligand binding to human NET (P < 0.001) only 1 hour after dosing. Plasma DHPG and DHPG/norepinephrine (ratio) during repeated posture tests were reduced significantly (P < 0.001) on day 5 and stayed significantly reduced up to 1 day after treatment. In CSF, both DHPG and the ratio were significantly reduced (P < 0.001) on day 18. Urine results showed significant decreases for both DHPG and the ratio (P = 0.010 to P < 0.001). Brain-derived neurotrophic factor in CSF was lesser than the limits of detection. The findings suggest that NET blockade can be assessed with DHPG concentration or with the ratio in plasma, CSF, and urine. The data suggest that DHPG is a useful biomarker to proactively assess the pharmacological activity of compounds intended to inhibit NET activity within the brain. The study shows that CSF is a medium for early identification and quantification of biomarkers useful in assessing novel neuroscience targets.

Similarity of insulin detemir pharmacokinetics, safety, and tolerability profiles in healthy caucasian and Japanese american subjects.

The objective of this study was to compare the pharmacokinetics of insulin detemir in three ascending doses in healthy Japanese and Caucasian subjects. This was an open-label, single-center, parallel-group design evaluating 30 subjects (15 Japanese and 15 Caucasians). Subjects received a total of three subcutaneous injections (one injection per visit) of insulin detemir (0.19, 0.38, 0.75 U/kg [1 U = 24 nmol]) in ascending order. Following drug administration, subjects received intravenous glucose in 0.5-mg/kg/min increments every 30 minutes, followed by a constant rate of 2.0 mg/kg/min for up to 12 hours. For pharmacokinetic evaluations, serial blood sampling was performed over a period of 30 hours after dosing. Of the subjects, 36 were enrolled, and 30 completed the study. There was a linear dose-response relationship between the three ascending insulin detemir doses and serum insulin detemir AUC values for both the Japanese and Caucasian subjects. The two dose-response regression lines had equivalent slopes but slightly different intercepts (although not statistically significant). This difference may be due to variation in AUC, body weight differences, or chance. Six subjects discontinued the study, 2 as a result of adverse events (blood draw-related ecchymosis and hypoglycemia). The most frequent treatment-emergent adverse events (TEAE) were headache, dizziness, and reactions related to blood draws/infusion sites. All TEAEs were mild to moderate in severity. The results show that an increase in insulin detemir dose will result in a similar increase in insulin detemir concentration in the two ethnic groups. Therefore, therapeutic dosing of insulin detemir is expected to be similar in both ethnic groups, with no special dose adjustment or algorithm based on race. Insulin detemir at 0.19, 0.38, and 0.75 U/kg was generally well tolerated in both Japanese and Caucasian subjects.