IngredientsEthyl oleate (EO), systematically named 9-octadecenoic acid ethyl ester, carries the CAS registry number 111-62-6 and is the ethyl ester of oleic acid. Its IUPAC name is ethyl (E)-octadecenoate, with the molecular formula C₂₀H₃₈O₂ and the InChI Key LVGKNOAMLMIIKO-VAWYXSNFSA-N. Common synonyms listed in pharmacopeial and trade sources include oleic acid ethyl ester, ethylis oleas, ethyl cis-9-octadecenoate, Crodamol EO, and Kessco EO, among others.
Ethyl oleate appears as a colorless to pale yellow, viscous oily liquid at room temperature, possessing a faint fatty odor, a density of approximately 0.87 g/cm³, a boiling point of 216–218 °C (at 15 mm Hg), and low solubility in water but high solubility in organic solvents such as ethanol and chloroform. The molecular weight is 310.51 g/mol, and the substance is almost insoluble in water but miscible with ethanol, dichloromethane, and petroleum ether, and can be mixed with isopropanol in any proportion.
Ethyl oleate is described in the USP as consisting of esters of ethyl alcohol and high molecular weight fatty acids, principally oleic acid. Its properties are similar to those of almond oil and peanut oil; however, it has the advantage of being less viscous than fixed oils and more rapidly absorbed by body tissues.
Oleic acid, the parent fatty acid from which ethyl oleate is formed, is the most widely distributed and the most extensively produced of all fatty acids in nature. Ethyl oleate is found naturally in many plant oils, including olive oil, pecan oil, canola oil, peanut oil, macadamia oil, sunflower oil, grape seed oil, sea buckthorn oil, sesame oil, and poppy seed oil. It is also a natural product found in Artemisia argyi with data available.
Beyond plants, ethyl oleate is produced endogenously in animal tissues. Ethyl oleate is produced by the body during ethanol intoxication; it is one of the fatty acid ethyl esters (FAEEs) produced after ingestion of ethanol. In honey bees, this transition is also biologically relevant: ethyl oleate is a primer pheromone produced by foragers when exposed to ethanol from fermented nectar.
Ethyl oleate is synthesized through the esterification of oleic acid with ethanol in the presence of an acid catalyst, resulting in a stable, biodegradable product that resists oxidation under normal conditions. Industrial grades may also be prepared by reaction with oleoyl chloride. Quality standards recognized for ethyl oleate as a pharmaceutical excipient include CP2020 (Chinese Pharmacopoeia), USP2022, EP11.0 (European Pharmacopoeia), BP2020 (British Pharmacopoeia), and the food-grade standard GB 29938-2013.
Ethyl oleate is regulated as a food additive by the U.S. Food and Drug Administration under "Food Additives Permitted for Direct Addition to Food for Human Consumption," 21 CFR 172.515. It has been evaluated by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) and declared safe when used as a flavoring agent in food.
Ethyl oleate does not have an established record of deliberate isolation and use as a named compound in traditional ethnobotanical or phytotherapeutic systems. Unlike whole plant preparations whose use histories span centuries, ethyl oleate is a defined chemical entity whose characterization and intentional application are modern. Historically, ethyl oleate has been utilized primarily in the pharmaceutical and food industries, particularly as a solvent and vehicle for lipophilic compounds, and more recently it has gained attention as an ingredient in nutritional supplements and parenteral nutrition formulations.
The compound does, however, arise naturally in traditionally fermented foods and beverages containing ethanol and oleic acid-rich oils. The biosynthetic pathway of ethyl oleate via esterification of oleic acid with ethanol means it is a trace constituent of fermented plant products. Its recognition as a distinct molecular entity came in the twentieth century alongside advances in lipid analytical chemistry.
In pharmaceutical practice, the earliest use of ethyl oleate as a named injectable vehicle is documented in the mid-twentieth century. Ethyl oleate is primarily used as a vehicle in specific parenteral preparations intended for intramuscular administration. Notably, Louis Bouveault used ethyl oleate to demonstrate Bouveault–Blanc reduction, producing oleyl alcohol and ethanol, a method which was subsequently refined and published in Organic Syntheses.
In vivo studies have demonstrated that ethyl oleate and other fatty acid esters are rapidly hydrolyzed to ethanol and free fatty acid. The absorption, distribution, and excretion of radiolabeled EO was studied in Sprague–Dawley rats after a single, peroral dose of 1.7 or 3.4 g/kg body weight compared with a radiolabeled triacylglycerol containing only oleic acid. Both test materials were well absorbed, with approximately 70–90% of the EO dose absorbed and approximately 90–100% of the triacylglycerol dose absorbed. At sacrifice 72 hours post-dose, tissue distribution of EO-derived radioactivity and triacylglycerol-derived radioactivity was similar. Both test materials were rapidly and extensively excreted as CO₂ with no remarkable differences between their excretion profiles.
Overall, these results demonstrate that the absorption, distribution, and excretion of radiolabeled EO is similar to that of triacylglycerol, providing evidence that the oleic acid moiety of EO is utilized in the body as a normal dietary triacylglycerol-derived fatty acid.
Ethyl oleate is a suitable solvent for steroids and other lipophilic drugs. In pharmaceuticals, ethyl oleate serves as a key excipient and vehicle for lipophilic drugs, particularly in intramuscular injections, where it enhances solubility and bioavailability of substances like steroids and vitamins while minimizing tissue irritation. Its viscosity is low compared with fixed vegetable oils, and it is easily absorbed by body tissues.
Ethyl oleate's penetration-enhancing activity is linked to its parent fatty acid, oleic acid. Long-chain fatty acids, especially oleic acid, are among the most widely investigated skin penetration enhancers. It is now well accepted that the mechanism by which fatty acids and alcohols increase skin permeability involves an interaction with the intercellular lipids in the stratum corneum. Alteration of the lipid bilayers has been assessed using differential scanning calorimetry (DSC) and Fourier infrared spectroscopy (FTIR). These methods indicate that the enhancer system may cause disruption of the ordered lamellar structure of the bilayers in the stratum corneum, leading to increased fluidization of the intercellular medium.
According to the lipid-protein partitioning (LPP) concept, permeation enhancers employ one of three main mechanisms: disrupting the lipid matrix of the stratum corneum, interacting with intracellular proteins, or enhancing the ability of the medication or solvent to penetrate into the stratum corneum.
FAEEs are produced by an enzymatic esterification of ethanol with free endogenous fatty acids, triglycerides, lipoproteins, and phospholipids by means of two enzymes: FAEE synthase and acyl-CoA/ethanol O-acyl-transferase (AEAT). FAEE synthase activity is present in microsomes and cytosol of affected organs. A search for the molecular mechanism underlying alcohol-induced end-organ damage has led to the discovery of a nonoxidative pathway for the metabolism of alcohol in several human tissues including heart, brain, pancreas, and liver. It has been revealed that nonesterified fatty acids are esterified with ethanol to produce FAEEs, neutral molecules which can accumulate in mitochondria and impair cell function.
In honey bees, ethyl oleate delays the nursing-to-foraging transition and acts as a primer pheromone produced by foragers when exposed to ethanol from fermented nectar. Two secreted α/β-hydrolases (BeeBase ID: GB11403 and GB13365) are responsible for the reversible esterification of ethanol with oleic acid to give ethyl oleate. Ethyl oleate is a primer pheromone that delays the onset of foraging in young workers. Honey bee workers biosynthesize more EO during the growing season than during the fall and winter months, reaching peak levels at late spring or summer.
The most clinically documented application of ethyl oleate is as a pharmaceutical vehicle for injectable preparations. Ethyl oleate is primarily used as a vehicle in specific parenteral preparations intended for intramuscular administration. It has also been used as a solvent for drugs formulated as biodegradable capsules for subdermal implantation and in the preparation of microemulsions containing cyclosporin and norcantharidin.
Evidence strength: The safety profile of ethyl oleate as a vehicle for injection has been established through pharmacopoeial monographs (USP, EP, BP) and regulatory review. Ethyl oleate is generally considered to be of low toxicity, and it has been found to cause minimal tissue irritation, with no reports of intramuscular irritation during use. Ethyl oleate has also been evaluated as a vehicle for subcutaneous injection. However, it is important to note that ethyl oleate is not currently approved by the U.S. Food and Drug Administration for any injectable formulation as a stand-alone new drug application; rather, it is used as a compounded or pharmacopoeial excipient.
One of the most widely encountered clinical uses of ethyl oleate is as the oil vehicle for compounded intramuscular progesterone injections, particularly in in-vitro fertilization (IVF) cycles. Because some patients may be allergic to sesame oil (the most common conventional vehicle), compounding pharmacies may use ethyl oleate to prepare daily doses of progesterone in fertility treatments and other applications related to hormone replacement therapy.
Evidence strength: The evidence base here consists primarily of pharmacological rationale (low viscosity, good biocompatibility), pharmacopoeial status, and clinical practice experience rather than randomized controlled trials comparing ethyl oleate-based formulations with other vehicles in fertility outcomes. No head-to-head RCT specifically evaluating ethyl oleate-based progesterone versus sesame oil-based progesterone in IVF has been identified in the peer-reviewed literature as of the time of this writing.
Several formal toxicological and clinical studies have evaluated the safety of orally ingested ethyl oleate, motivated partly by its use as a food flavoring agent regulated under FDA 21 CFR 172.515.
Animal (subchronic) study: A 91-day feeding study in Sprague–Dawley rats examined the safety of ethyl oleate at levels of 0, 3.3, 6.7, and 10% by weight in AIN-93G purified diet (the high-dose males and females consumed 5.5 and 6.1 g/kg/day EO, respectively), with all diets calorie- and fat-matched using high oleic safflower oil as the control fat. EO in the diet was well tolerated and there were no toxicologically significant findings in any of the measured parameters, including clinical observations, body weight gains, fecal appearance, ophthalmic examinations, hematology, clinical chemistry, urinalysis, organ weights, histopathology, or male and female reproductive assessments.
Human clinical trial: To confirm the expected safety of EO in humans, a total of 235 subjects participated in a 12-week trial where two levels of ethyl oleate in a milk-based beverage were investigated: 8 g/day in a single serving (approximately 0.1 g/kg) and 16 g/day taken in two divided servings (approximately 0.2 g/kg). Results showed that the incidence of reported adverse events was similar between the EO and control groups. Analysis of comprehensive laboratory data revealed no EO exposure-related, clinically significant adverse changes in laboratory parameters. These studies demonstrated that EO has a highly favorable safety profile and is well tolerated in the diet.
Evidence strength: The oral safety database for EO is relatively robust for a food-additive excipient, with a well-conducted 91-day rat study and a randomized, controlled human trial (n=235, 12 weeks) supporting its tolerability at levels up to 16 g/day. These data underpinned JECFA's evaluation. The evidence is adequate for the conclusion of oral safety at intended food-flavoring use levels, but falls short of demonstrating any positive health effect.
Ethyl oleate is extensively studied as the oil phase in self-microemulsifying and self-nanoemulsifying drug delivery systems (SMEDDS/SNEDDS) intended to enhance the oral bioavailability of poorly water-soluble drugs. This is a pharmaceutical formulation role rather than a health-promoting role of EO itself, but is a significant area of applied research.
In an oleanolic acid SMEDDS study, an optimal formulation was established as 50% ethyl oleate as the oil, 35% Cremophor EL as the surfactant, and 15% alcohol as the cosurfactant. The results of a pharmacokinetic study showed that the relative bioavailability of oleanolic acid was markedly improved, being approximately 507% that of the oleanolic acid tablet.
In one study, two SMEDDS formulations of 9-nitrocamptothecin developed from a mixture of ethyl oleate with Tween 80 or Cremophor EL and PEG-400/ethanol represented significant enhancement of oral bioavailability (37.03% and 37.91%) in rats compared with suspension and solution forms.
In a relugolix SMEDDS study, S-SMEDDS were shown to enhance drug absorption through lymphatic absorption and inhibition of intestinal transporter, and in vivo pharmacokinetic evaluation demonstrated that the oral bioavailability of the solid SMEDDS formulation was 1.9 times higher than that of drug suspensions.
Evidence strength: All SMEDDS data cited here are animal pharmacokinetic studies (predominantly in rats). Ethyl oleate functions as an excipient oil in these systems; any bioavailability enhancement is a property of the complete formulation system, not of ethyl oleate per se. Human clinical data for ethyl oleate-based SMEDDS are limited, and the body of evidence remains at the preclinical stage.
Microemulsion formulations containing ethyl oleate have been proposed for topical and ocular delivery, and for liver targeting following parenteral administration. Ethyl oleate has been used in topical gel formulations and in self-microemulsifying drug delivery systems for oral administration.
Ethyl oleate is used as a solvent, a transdermal absorption enhancer, a lubricant, and a plasticizer in formulations. Its skin penetration-enhancing effect is attributed to the oleic acid moiety, which disrupts the ordered lamellar lipid structure of the stratum corneum.
Evidence strength: Evidence for ethyl oleate as a transdermal enhancer is based primarily on in vitro permeation studies and formulation research. Controlled human skin penetration data with ethyl oleate specifically are limited; the established mechanistic data are derived from the parent compound oleic acid.
One of the most scientifically significant areas in which ethyl oleate has received rigorous study is as a biomarker of prenatal alcohol exposure, analyzed from neonatal meconium (the first fecal material passed by newborns).
Ethyl oleate was the FAEE that correlated most strongly with maternal self-reported drinking, especially with the average ounces of absolute alcohol ingested per drinking day. Ethyl oleate concentration in meconium assayed by GC/MS/MS provides a highly sensitive and specific indicator of maternal alcohol use during pregnancy. Ethyl oleate was most strongly related to drinking in the second and third trimesters (Pearson r=.55 and .40, respectively).
At a threshold of 1.5 average ounces of absolute alcohol ingested per drinking day, the area under the receiver operating characteristic curve was 0.92 (95% confidence interval, 0.74–0.97). Using a cut-off value of 32 ng/g, sensitivity was 84.2% and specificity was 83.3%. Ethyl oleate concentration in meconium assayed by GC/MS/MS provides a highly sensitive and specific indicator of maternal alcohol use during pregnancy.
FAEEs do not cross the placenta into the fetal circulation, and because they can be detected in fetal matrices, must be produced in the fetus itself from the ethanol which crosses the placenta.
In a sheep model, ethyl oleate, ethyl linoleate, and ethyl arachidonate levels were significantly higher in ethanol-exposed fetuses, and ethyl oleate was the FAEE that correlated most strongly with alcohol ingestion during pregnancy, with the greatest area under the curve (0.94).
In fetal sheep, meconium FAEE could serve as a biomarker of daily ethanol exposure in late gestation and could identify fetuses with subtle ethanol-induced toxic effects in various organs, illustrating the potential for using meconium FAEE to identify neonates at risk for dysfunction of major organs following in-utero ethanol exposure that does not result in overt physical signs of ethanol teratogenicity.
In a national Canadian study, FAEE in meconium was quantified by headspace solid-phase microextraction coupled with GC-MS. Out of 1,315 samples collected in 10 Canadian obstetric units between 2008–2011, the estimated prevalence of positive meconium FAEE ranged between 1.16% and 2.40%, translating into at least 1,800 new cases of FASD in Canada each year.
Evidence strength: The biomarker evidence base is strong. Multiple prospective and validation studies across human and animal models support the use of meconium ethyl oleate quantified by GC/MS as a sensitive and specific biomarker of prenatal alcohol exposure, particularly in the second and third trimesters.
The scientific literature on ethyl oleate and organ toxicology is tightly linked to alcohol metabolism research, as ethyl oleate is a major endogenous FAEE formed when ethanol is consumed.
FAEEs are nonoxidative ethanol metabolites shown to produce toxic effects in the liver and pancreas in vivo and in vitro. Alcohol-intoxicated humans have high levels of FAEEs, nonoxidative products of ethanol metabolism, in blood, pancreas, and liver. FAEEs at concentrations found in human plasma produce a pancreatitis-like injury in rats, providing direct evidence that FAEEs can produce organ-specific toxicity. Thus, FAEEs may contribute to acute alcohol-induced damage to the pancreas.
Nonesterified fatty acids are esterified with ethanol to produce FAEEs, neutral molecules which can accumulate in mitochondria and impair cell function. The observation that FAEEs are synthesized at high rates in the heart and other organs that lack oxidative ethanol metabolism provides a plausible link between the observed tissue damage, the ingestion of alcohol, and the subsequent development of alcohol-induced heart muscle disease.
Ethyl oleate, ethyl stearate, and ethyl palmitate were the predominant FAEE formed in the intact organism. Ethanol-induced FAEE may play a role in the development of alcohol-related injuries to the lung.
Notably, the relative toxicity of FAEEs versus their parent free fatty acids has been examined. Unsaturated fatty acids at equimolar concentrations to FAEEs induced a larger increase in cytosolic calcium, mitochondrial depolarization, and necro-apoptotic cell death. Glyceryl tri-oleate, but not oleic acid ethyl ester, resulted in 70% mortality with increased serum oleic acid, a severe inflammatory response, worse pancreatic necrosis, and multisystem organ failure. These data show that fatty acids are more likely to worsen acute pancreatitis than FAEEs. These observations correlate well with the high pancreatic FAEE concentrations in alcoholics without pancreatitis and high fatty acid concentrations in pancreatic necrosis. Conversion of free fatty acids to FAEE may therefore ameliorate acute pancreatitis in alcoholics.
Some research literature implicates FAEEs such as ethyl oleate as the toxic mediators of ethanol in the body, affecting the pancreas, liver, heart, and brain. Ethyl oleate may be the toxic mediator of alcohol in fetal alcohol syndrome. This remains an active area of research with mechanistic hypotheses under continued investigation.
Ethyl oleate is employed across several dosage forms, each associated with distinct reported use levels:
The oral ingestion of ethyl oleate has been carefully studied and due to rapid degradation in the digestive tract, it appears safe for oral ingestion. As stated in a peer-reviewed safety assessment published in Regulatory Toxicology and Pharmacology (2003), "the safety of the use of ethyl oleate in food is supported by metabolism data in rats and clinical safety data in humans."
Ethyl oleate can dissolve some rubbers and cause swelling, and it can also react with oxidants. These properties are relevant to packaging and formulation design.
Ethyl oleate should be stored in a cool, dry place in a small, well-filled, well-closed container protected from light. When a partially filled container is used, the air should be replaced by nitrogen or another inert gas to minimize oxidation. Antioxidant materials have been used to stabilize ethyl oleate as a nonaqueous solvent for injections.
Although ethyl oleate is regarded as well-tolerated as a pharmaceutical vehicle, hypersensitivity reactions have been documented clinically, particularly in the context of its use as a vehicle for intramuscular progesterone. In a published case, following a round of IVF containing progesterone in ethyl oleate, a patient experienced a delayed diffuse maculopapular rash, pruritus, and mild lip and scalp swelling. Immediate and delayed skin testing to ethyl oleate, polyethylene glycol, sesame oil, polysorbate, and progesterone were negative in that case, suggesting the reaction may have been mediated by autoimmune progesterone sensitization rather than direct EO allergy. Distinguishing reactions to the oil vehicle from reactions to the active hormone requires careful clinical evaluation.
The safety considerations regarding ethyl oleate as an endogenous FAEE are fundamentally different from those related to its exogenous administration as a pharmaceutical excipient or dietary substance. Several studies have proposed varied theories to explain the deleterious effects of alcohol-generated FAEEs, including release of free fatty acids by FAEE, increased intracellular Ca²⁺, mitochondrial dysfunction, increased oxidative stress, and shift of acinar cell apoptosis to necrosis. These effects are relevant only in the context of significant alcohol consumption, not from pharmaceutical or dietary exposure to exogenous ethyl oleate.
The half-life of plasma FAEE is approximately one minute; they undergo hydrolysis in plasma and uptake by organs. FAEEs bind to myocardial mitochondria in vitro and in vivo, where the mitochondria hydrolyze FAEEs to fatty acids, which are uncouplers of oxidative phosphorylation. This may account for the impaired mitochondrial function and inefficient energy production associated with the toxic effects of ethanol on the heart.
Because ethyl oleate contains an unsaturated fatty acid chain, oxidative degradation to peroxides is a potential concern during storage or formulation, particularly for injectable use. A suitable antioxidant may be included in pharmacopoeial preparations. Peroxide content monitoring is a relevant quality indicator for ethyl oleate preparations intended for parenteral use.
Health conditions that Ethyl oleate may help support.
Body systems that Ethyl oleate may help support.
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