Background: Theobromine (3,7-dimethylxanthine) has various clinical properties including vasodilation, bronchodilation, and diuresis in humans. It is currently under clinical investigation for cough suppression. The aim of this study was to evaluate the safety and pharmacokinetic characteristics after

multiple oral administrations of theobromine 500 mg capsules in healthy male volunteers.

Methods: A single-arm, multiple-dosing study was conducted in 12 healthy male volunteers. All subjects orally received the study drug every 12 hours for 7 days. Blood samples were collected up to 12 hours after first dosing and up to 48 hours after last dosing. Plasma concentrations of theobromine were analyzed using high-performance liquid chromatography. Safety assessments, including monitoring adverse events, laboratory tests, vital signs, ECGs, and physical examinations, were performed throughout the study.

Results: Pharmacokinetic steady-state was achieved before the last dosing. Median time to peak concentration at steady state (Tmax,ss) was 1.8 hr. Mean terminal half-life was 13.4 hr, and mean peak-trough fluctuation was 47.5% at steady state. At steady state, mean peak concentration (Cmax,ss)

and area under the plasma concentration-time curve during a dosing interval (AUCτ,ss) was 22.0 μg/mL (coefficient of variation, CV: 13.8%) and 213.9 μg*h/mL (CV: 17.6%), respectively. Mean accumulation ratio ranged from 1.8 to 2.8 after multiple administrations. There were neither any serious adverse

events nor remarkable findings regarding safety.

Conclusion: Theobromine capsules were safe and well-tolerated when administered twice daily at dose of 500 mg for 7 days. This study showed the relatively low inter-individual variation in terms of Cmax and AUC, and moderate accumulation after multiple dosing. This study provided evidence for a twice-a-day dosing regimen of theobromine 500 mg capsules for treatment of chronic cough.