Herbal Supplements and the Brain: Understanding Their Health Benefits and Hazards (Richard Stout's Library) by S. J. Enna & Stata Norton

Author:S. J. Enna & Stata Norton
Language: eng
Format: epub
Publisher: FT Press
Published: 2012-06-16T16:00:00+00:00

Pharmacokinetics

Only a few pharmacokinetic studies have been performed on lavender oil and its constituents. This is presumably because lavender oil has historically been systemically administered either by inhalation of its vapors or by the oral consumption of the small quantities present in lavender teas or in food. Only recently has the oil been packaged and sold in a formulation suitable for oral administration of a fixed dosage for medicinal purposes. Assuming these products are popularized, it is anticipated that detailed pharmacokinetic studies will in the future be performed to define more precisely the extent of absorption, distribution, and metabolism of what are believed to be the pharmacologically active constituents in lavender.

Because lavender oil is contained in a number of liniments and cosmetic creams, there have been studies to determine whether linalool and linalyl acetate are absorbed through the skin. In vitro experiments suggest that both compounds make their way into deeper layers of the skin shortly after topical application.11,12 The results indicate that linalool is more readily absorbed through skin than linalyl acetate.

In vivo studies of cutaneous absorption have been conducted with human subjects. Similar to the in vitro findings, these experiments indicate that linalool is absorbed through the intact skin. In one study, topical application of linalool was associated with a fall in blood pressure and skin temperature, suggesting a systemic response to this agent. These subjects did not display any signs of an increase in mood or in feelings of well being, indicating that the quantities absorbed were insufficient to affect the central nervous system.13 Linalool is detectible in deeper skin layers within an hour of its placement on human skin. These levels declined within one to two hours after linalool was removed from the surface of the skin.14 Evidence indicating that these compounds penetrate the skin completely is provided by the finding that both linalool and linalyl acetate are detected in blood following topical application of lavender oil.15

These data suggest that linalool and linalyl acetate, and perhaps other constituents of lavender oil, are sufficiently lipid soluble to cross the skin and accumulate in the systemic circulation. Assuming they are not rapidly metabolized in the intestine, these results suggest these compounds will readily cross from the gastrointestinal tract into blood when taken orally. It is not possible from these reports, however, to estimate the bioavailability, or fraction of an administered dose of these plant constituents, that will appear systemically, and whether either of these compounds penetrates into the brain in sufficient quantities to modify nervous system activity.

In vitro experiments indicate that linalool is metabolized by human liver enzymes.16 One of the resultant compounds, 6,7-epoxy-linalool, is thought to contribute to the skin irritation that some experience following the topical application of lavender oil. In vivo studies revealed that linalool was metabolically converted in rats to a number of different compounds following its continuous oral administration.17 Consumption of linalool increased significantly the levels of certain drug metabolizing enzymes in rat liver. These findings confirmed the results of earlier studies with

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