Pharmacokinetics of linalool and linalyl acetate, the two main constituents of silexan, an essential oil from Lavandula angustifolia flowers, in rats

Silexan is the active ingredient in Lasea^®, which has recently been approved for the treatment of restlessness and mild anxiety in Germany. The naturally occurring enantiomers R-(-)linalool L and R-(-)linalyl acetate (LA) are the main constituents of silexan representing 70–80% of the total oil. We investigated the bioavailability and organ distribution of L and LA in rats by headspace GC-MS after administration of silexan or the single constituents. The peak concentrations of L after 100mg/kg silexan was 77ng/ml in plasma, 2287ng/g in liver, 670ng/g in kidney, 2085ng/g in fat and 164ng/g in brain tissue. LA was only measured in the brain (31ng/g). Administration of 28,9mg/kg L which corresponds to the amount contained in 100mg silexan, resulted in peak concentrations of 33ng/ml in plasma, 218ng/g in liver, 541ng/g in kidney, 1140ng/g in fat and 43ng/g in brain tissue. The gavage of 36.8mg/kg of LA, the equimolar amount to 28.9mg L resulted in peak L concentrations of 10ng/ml in plasma, 274ng/g in liver, 255ng/g in kidney, 244ng/g in fat and 0ng/g in brain tissue. LA itself was only found in the brain and in fat tissue. The results indicate that the bioavailability of L is generally higher when applied as total oil in comparison to the application of the single constituents. Interestingly, LA is very rapidly metabolized into L and can only be detected in the brain and in fat tissue.

Keywords: Pharmakokinetics, Lavandula, Silexan, Bioavailability