Effects of Palmijihwang-hwan: A Herbal Formula on the Pharmacokinetics of Tamsulosin in Rats

Background Tamsulosin is an alpha(1)-adrenoceptor antagonist used to treat lower urinary tract symptoms (LUTS) and benign prostatic hyperplasia (BPH). Palmijihwang-hwan (PMJHH) is a traditional herbal formula for treating prostatic disorders and is often used with tamsulosin for treating LUTS/BPH. The co-administration of herbal medicines and conventional drugs increases the potential for clinically considerable herb-drug interactions. Hence, it is important to evaluate the safety of such combinations of drugs. This study aimed to investigate the influence of PMJHH on the pharmacokinetics of tamsulosin in rats. Materials and Methods We developed and validated a simple and rapid method to determine the plasma levels of tamsulosin in rats using an ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) system. After oral administration of tamsulosin (2 mg/kg), either alone or in combination with PMJHH (930 mg/kg), to rats, blood samples were collected at various times and used for pharmacokinetic studies. The pharmacokinetic parameters were analyzed using a non-compartmental model. Results Compared to tamsulosin alone, co-administration of PMJHH had no significant effects on any pharmacokinetic parameters of tamsulosin, including maximal plasma concentration (C-max), time to C-max (T-max), terminal elimination half-life (t(1/2)), AUC from time 0 to the last observation (AUC(0-t)), mean residence from time 0 to infinity (MRT0-infinity), apparent oral clearance (Cl/F), and apparent volume of distribution during terminal elimination (Vz/F). Conclusion The pharmacokinetics of tamsulosin were not affected by the co-administration of PMJHH. Our findings, therefore, validate the safety of the combination of tamsulosin and PMJHH commonly used for treating LUTS/BPH.