Abstract
Background: Naftopidil is a selective ${\alpha}_1$ adrenergic receptor antagonist which is used for the treatment of dysuria caused by benign prostatic hyperplasia. We investigated the pharmacokinetic characteristics and tolerability of naftopidil after a single oral dose in healthy Korean male volunteers. Methods: Sixteen subjects were allocated into two groups (8 for naftopidil 50 mg and 75 mg, 8 for naftopidil 25 mg and 100 mg). Serial blood samples for pharmacokinetics were collected up to 24 hours after drug administration. Naftopidil plasma concentrations were determined by HPLC. The pharmacokinetic parameters were calculated by noncompartmental methods. Tolerability assessments including vital signs, 12-lead ECG, clinical laboratory parameters, and adverse events were conducted. Results: The median time of maximum observed plasma concentration ($T_{max}$) was 0.5 h in all dose groups. The maximum plasma concentration ($C_{max}$) of 25, 50, 75 and 100 mg dose group were $44.0\;{\mu}g/L$, $88.9\;{\mu}g/L$, $114.3\;{\mu}g/L$, and $179.5\;{\mu}g/L$, respectively. The area under the concentration-time curve to the last measured concentration over the limit of quantitation ($AUC_{last}$) of respective dose groups were $71.1\;{\mu}g{\ast}h/L$, $178.7\;{\mu}g{\ast}h/L$, $298.3\;{\mu}g{\ast}h/L$, and $342.6\;{\mu}g{\ast}h/L$, respectively. Conclusion: The results of this study indicate that the systemic exposure of naftopidil expressed $AUC_{last}$ and $C_{max}$ was increased dose proportionally, and all doses. Up to 100 mg were well tolerated without serious adverse events in healthy Korean male volunteers.
