Plasma and dermal pharmacokinetics of terpinen-4-ol in rats following intravenous administration

Terpinen-4-ol, a naturally occurring monoterpene, has been shown to possess antibacterial, antioxidant and anti-inflammatory activities. Furthermore, recent reports have demonstrated that terpinen-4-ol could be developed as new therapies against melanoma either in systemic administration or targeted drug delivery. The purpose of this study was to investigate the pharmacokinetics of terpinen-4-ol in rat plasma and dermal tissue following intravenous (i.v.) bolus injection of terpinen-4-ol at a dose of 2 mg/kg. Unbound concentrations of terpinen-4-ol in dermis were continuously determined by dermal microdialysis. Simultaneously, a conventional blood sampling was performed. The concentrations of terpinen-4-ol in plasma and microdialysates were determined by validated gas chromatography-mass spectrometry. Following i.v. bolus administration, terpinen-4-ol rapidly distributed into the dermis and reached relatively low levels with an average maximum concentration (Cmax) of 0.10 +/- 0.06 microg/ml in comparison with a plasma Cmax of 6.30 +/- 1.90 microg/ml. The free terpinen-4-ol concentrations in dermal tissue were lower than the corresponding total and free plasma concentrations for the entire length of study, indicating that plasma levels do not provide information of actual terpinen-4-ol concentrations in the skin. This study demonstrates that dermal microdialysis is an effective and minimally invasive tool to evaluate the dermal pharmacokinetics of terpinen-4-ol following systemic administration.