In Phase 1 clinical studies conducted in Japanese and Caucasian subjects, droxidopa was well tolerated and no differences were noted in oral absorption between the two groups. Apart from a moderate increase in heart rate in one Caucasian subject (receiving 600 mg droxidopa), which was considered to be possibly related to study medication, there were no other adverse events (AEs) that were considered to be related to droxidopa treatment. The maximum plasma concentration (Cmax) was reached between 2 and 3 hours after single, oral doses of droxidopa (100 to 900 mg). The plasma elimination half-life (t½) of droxidopa was 1.4 - 1.5 hours and approximately 15% of the drug was recovered unchanged in the urine. No drug accumulation was observed after multiple oral dosing with droxidopa (300 mg twice daily for 5 days).