Bioavailability and Pharmacokinetics of Natural Volatile Terpenes in Animals and Humans

Abstract

Herbal medicinal products containing natural volatiles are used in the treatment of gastrointestinal diseases, pain, colds and bronchitis. Many pharmacological studies report a wide variety of in vitro effects, with anti-inflammatory and antimicrobial activities investigated most frequently. In comparison, relatively few studies on the bioavailability and pharmacokinetics have been carried out. Thus, the relevance of the in vitro activity to the therapeutic effects found in individual studies or documented in textbooks of phytotherapy is still not established. Further studies with essential oils and their single compounds providing supporting evidence of efficacy and demonstrating systemic availability are necessary. Such data could also be important in the context of safety.Key words: Terpenes, volatiles, herbal medicinal products, bioavailability, pharmacokinetics. IntroductionEssential oils are mixtures of lipophilic, liquid, volatile, and often terpenoid compounds present in higher plants. More than 3000 compounds have been described so far (1). The clinical efficacy of volatiles is particularly well-established for chronic pulmonary obstruction and acute bronchitis. For these indications clinical trials have been carried out with products containing 1,8-cineole (2), (3), (4), standardised myrtol (1,8-cineole, a-pinene, limonene) (5) and thyme extract (6), (7). Further clinical studies have been carried out with peppermint oil for the treatment of irritable bowel syndrome (8), (9), non-ulcer dyspepsia (10), and tension-type headache (11). Numerous essential oils and their components have shown antimicrobial or antimycotic activity in in vitro studies (12), (13), (14), (15), (16).Various other in vitro activities of volatile oils or compounds have been reported. However, the clinical relevance of these activities depends on the systemic availability of these compounds in the respective target organs. Thus, investigation of absorption, distribution and metabolism is necessary to link in vitro with in vivo data. They may also be important in context of the safety of herbal medicinal products containing natural volatiles. However, pharmacokinetics of volatile natural compounds have not yet been investigated satisfactorily. For several monoterpenoid and phenylpropanoid compounds there is a large amount of experimental data, but crucially ± especially with respect to humans ± pharmacokinetic data are lacking.This article reviews the data currently available on the systemic fate of natural volatile terpenes and phenylpropanes. Unfortunately, methodological details, particularly concerning validation of the analytical methods used have not been published for most of the studies. Therefore the results of those studies discussed here have to be considered cautiously, since the assays used might not match the requirements for analytical validation. Absorption and Systemic Availability Dermal absorptionPreparations of eucalyptus oil or mountain pine oil containing a-and b-pinene, camphor, 3-carene, and limonen...

Terpene accumulation in muscle and fatty tissues of calves supplemented with essential oils

“…The excess terpene may have failed to be absorbed through the digestive tract, or may have been readily eliminated. This low accumulation is consistent with the high clearance values observed by Kohlert et al (2000), who determined the average half-life of a variety of monoterpenes and oxygen-containing derivatives to be about one hour.…”

“…Nevertheless all this information has been provided by pharmacological studies in non-ruminant species (Kohlert et al, 2000), by studies on terpene elimination in milk (Viallon et al, 2000;Fernandez et al, 2003), or by studies in which terpene ingestion was not controlled (Cornu et al, 2001a,b;Priolo et al, 2004). Specific difficulties hinder the study of terpene fingerprints in ruminant meat products.…”

Biosynthesis and Therapeutic Properties ofLavandulaEssential Oil Constituents

“…Kohlert et al [38] found that there is little risk in accumulation of these compounds as they likely have a short half-life (hours) in the human body and are quickly eliminated. It was concluded that most of the essential oil constituents are metabolized into carbon dioxide by the body or excreted in conjugated form by the kidneys, with a small fraction of inhaled terpenoids released from the lungs during exhalation [38].…”

Essential oils in the initial phase of broodstock diets of Nile tilapia

“…The site of intestinal absorption of essential oils in monogastrics might influence its effect on the animal. Kohlert et al (2000) observed that the absorption of thymol in humans occurs in the upper intestine. In pigs, essential oils can be absorbed in the proximal portion of the intestine, and therefore, the antimicrobial activity in the distal portion of the intestine is limited (Muhl and Liebert, 2007).…”