Ok, so here is what I have dug up:
(Prepare for a long post)
Carvacrol and thymol are both monoterpenes, and I know many of them make it through digestion but the class can have pretty different compounds. Fundentals of
Pharmacognosy and Phytotherapy states "Geranyl pyrophosphate can by cyclized to give cyclic monoterpenes, which may be fully saturated, partially saturates, or fully aromatic products of which menthol, piperiton, and carvacrol are examples, respectively. (So carvacrol, the prevalent monoterpene, is usually fully aromatic in its natural state. You wouldn't be digesting it, but rather inhaling it unless you used an extract somehow.)
Carvacrol isn't noted for being antimicrobial, but that it "shows strong antifungal and antihelminthic properties." Not really sure how that would work as a fully aromatic compound, so I assumed it is the thymol and other compounds that are effective as an antimicrobial.
In the chapter on infectious diseases, it states, "thymol has a range of antibacterial and antifungal properties and is likely to be produced by the plant to protect itself from plant pathogenic microbes..."
Oregano is again not mentioned in the chapters on specific species but thyme is. Under constituents, "The active principle is the volatile oil, which has the major constituent thynol, with lesser amounts of carvacrol, 1,8-ceneole, borneol, thymol methyl, and alpha-pinene. However, the flavanoids, (aligning, leveling, thymonon, etc.) and the polyphenol acids (labiatic, rosmarinic and caffeic) are expected to contribute to the anti-inflammatory and antimicrobial effects." It also goes on to mention that it relaxes the smooth muscles of the trachea and ileum. Ok, so now we know the specific compounds.
Buhner's
Herbal Antibiotics states:
"Thyme essential oil, in tiny doses, one or two drops, when taken directly by the mouth will enter the blood stream immediately. If combined with herbs such as crytolepis, it will potentially their action against Gram-negatice bacteria. Remember,
Tiny doses."
Nothing on oregano specifically.
In
Medical Herbalism, it says of thymol that it may irritate gastric mucosa. (I think that's why I didn't think it was broken down completely. I remembered that passage.)
It also has oreanum marjorana (but not vulgaris) listed as a mild antimicrobial with secondary action of diaphoretiv. Thymus vulgaris is listed as a strong antimicrobial with an affinity for the respiratory and skin tissues, with expectorant effects and these secondary actions: anticatarrhal, antispasmodic, astringent, carminative, and emmeagogogue.
Now, I dug a bit further and found these studies:
https://link.springer.com/article/10.1007/s00204-017-2062-2
This one shows that some monoterpenes can cause liver toxicity because they reach the liver and form toxic metabolites. It does not mention any of the oregano terpenes specifically, so I found this study, which finally gives us the answer:
https://www.frontiersin.org/articles/10.3389/fphar.2017.00380/full
It states:
"Pharmacokinetics of Thymol
Absorption
Previous reports have revealed the rapid absorption of thymol following oral administration and its degradation in the stomach or intestine (Michiels et al., 2008; Anderson et al., 2012). A report from Schroder and Vollmer (1932) has evidenced the presence of thymol in the stomach, intestine, and urine after its oral administration with sesame oil at a dose around 500 mg in rats and 1–3 g in rabbits. A single dose of thymol (1 or 3 g) encapsulated in gelatin capsule administered to dogs showed the presence of thymol conjugates in urine (22 or 34%) after 3–4 h following urine and fecal analysis (Robbins, 1934). Oral administration of a single dose of thymol (50 mg/kg) was rapidly absorbed and slowly eliminated approximately within 24 h (Nieddu et al., 2014). The maximum concentration (Tmax) was reached after 30 min, while approximately 0.3 h was needed for the half-life of the absorption phase (t1/2). The lower concentrations of thymol were recovered in the liver, lungs, kidneys, and muscles while its higher concentrations were detected in the mucosa and other inner contents of the intestines indicating its partial absorption (Nieddu et al., 2014). According to the report of Kohlert et al. (2002), after the intake of one Bronchipret® TP tablet that is equivalent to 1.08 mg of thymol, the plasma concentrations of thymol metabolites were detectable after 20 min. The rapid absorption of thymol indicates that it’s mainly absorbed in the upper component of the gut. In healthy volunteers, the oral administration of one Bronchipret® TP tablet resulted in a peak plasma concentration (Cmax) of 93.11 ng/ml, Tmax of 1.97 h, t1/2 of 10.2 h, area under time curve from time 0 to clast (AUC0→clast of 837.3 ngh/ml, mean residence time after extravascular administration (MRTabs) of 12.6 h and a mean absorption time (MAT) of 0.53 h (Kohlert et al., 2002). It also had a total body clearance of 1.2 l/h, volume of distribution at steady state of 14.7 l and a volume of distribution during the elimination phase of 17.7 h was reported in healthy humans (Kohlert et al., 2002).
Distribution
Free thymol is usually not detectable in human plasma. It is circulated as thymol sulfate, not glucuronide, in the blood stream as detected by liquid chromatography-mass spectrophotometry/mass spectrophotometry (LC-MS/MS). Thymol sulfate has been detected in plasma 20 min after administration. The maximum plasma levels (93.1 ± 24.5 ng/ml) of thymol were reported after 1.97 ± 0.77 h of administration. After administration the bioavailability of thymol measured in plasma as thymol sulfate was found to be about 16%. It is eliminated by kidneys and is measured in the urine as thymol conjugates. The volume of distribution (Vdss/f) of 14.7 L has revealed that thymol sulfate mainly resides in the extracellular space (Kohlert et al., 2002).
Metabolism
Thymol undergoes glucuronidation by uridine 5′-diphospho-glucuronosyltransferase (UGT) following secretion into the proximal tubule (Raoof et al., 1996; Shipkova et al., 2001). The absence of thymol glucuronide in plasma could be due to the lower activity of hepatic UGT compared to sulfotransferase and the formation of glucuronide was shown only at much higher doses (Ogata et al., 1995). In healthy human volunteers, thymol (0.6 g/kg) was metabolized to thymol sulfate, thymol glucronide and thymol thymohydroquinone sulfate and it was excreted in urine (Takada et al., 1979).
Elimination
The elimination of thymol conjugates in urine was detectable for the first 24 h, with the majority being eliminated after 6 h. The combined amount of both thymol sulfate and glucuronide excreted in urine during the first 24 h was 16.2 ± 4.5% of thymol intake. The renal clearance was calculated to be 0.271 ± 0.7 L/h (Kohlert et al., 2002). Takada et al. (1979) studied the metabolism of thymol in rabbits and humans, wherein thymol (0.5 g/kg) fed to rabbits metabolized to thymol glucuronide as the main metabolite of thymol and eliminated as glucuronic acid and sulfuric acid metabolites (Takada et al., 1979). Austgulen et al. (1987) reported the rapid excretion of thymol and its metabolites in the urine of male albino Wistar rats after thymol was dosed by gavage (1 mM/kg) as analyzed by capillary gas chromatography–mass spectrometry (GC-MS). Williams (1959) summarized the previous reports on the metabolism of thymol and reported its excretion as sulfate and glucuronide conjugates in the urine of dogs, rats and humans. Around 1g (one third) of the dose was excreted in the urine of dogs while feces were found to be devoid of thymol (Robbins, 1934)."
So, all that to say- it seems like it makes it through the body as thymol sulfate and is excreted through urine.
That last study is really interesting and goes into in vivo animal studies (not human) and other pharmacological applications. I learned a lot about how it reacts to cancer cells, actually, and I think I might add some oregano oil or thyme oil to my daily routine.
Sorry for writing such a long post. This is the kind of stuff I love and get geeky about.
