This article is about pharmacodynamics and pharmacokinetics of ethanol. For ethanol as a psychoactive drug, seealcohol (drug). For alcohols used in medicine, seealcohols (medicine). For the substance in general, seeEthanol.
Constant-rate elimination at typical concentrations:[5][6][4] • Range: 10–34 mg/dL/hour • Mean (men): 15 mg/dL/hour • Mean (women): 18 mg/dL/hr At very high concentrations (t1/2): 4.0–4.5 hours[3][2]
Thepharmacology of ethanol involves both pharmacodynamics (how it affects the body) and pharmacokinetics (how the body processes it). In the body,ethanol primarily affects the central nervous system, acting as a depressant and causing sedation, relaxation, and decreased anxiety. The complete list of mechanisms remains an area of research, but ethanol has been shown to affect ligand-gated ion channels, particularly theGABAA receptor.
After oral ingestion, ethanol is absorbed via the stomach and intestines into the bloodstream. Ethanol is highly water-soluble and diffuses passively throughout the entire body, including the brain. Soon after ingestion, it begins to be metabolized, 90% or more by the liver. Onestandard drink is sufficient to almost completely saturate the liver's capacity to metabolize alcohol.[citation needed] The main metabolite is acetaldehyde, a toxic carcinogen. Acetaldehyde is then further metabolized into ionic acetate by the enzyme aldehyde dehydrogenase (ALDH).Acetate is not carcinogenic and has low toxicity,[9] but has been implicated in causinghangovers.[10][11] Acetate is further broken down into carbon dioxide and water and eventually eliminated from the body through urine and breath. 5 to 10% of ethanol is excreted unchanged in the breath, urine, and sweat.
Beginning with theGin Craze, excessive drinking and drunkenness developed into a major problem for public health.[12][13] In 1874,Francis E. Anstie's experiments showed that the amounts of alcohol eliminated unchanged in breath, urine, sweat, and feces were negligible compared to the amount ingested, suggesting it was oxidized within the body.[14] In 1902, Atwater and Benedict estimated that alcohol yielded 7.1 kcal of energy per gram consumed and 98% was metabolized.[15] In 1922, Widmark published his method for analyzing the alcohol content of fingertip samples of blood.[16]Through the 1930s, Widmark conducted numerous studies and formulated the basic principles of ethanol pharmacokinetics for forensic purposes,[17] including the eponymous Widmark equation. In 1980, Watson et al. proposed updated equations based ontotal body water instead of body weight.[18] The TBW equations have been found to be significantly more accurate due to rising levels ofobesity worldwide.[19]
The principalmechanism of action for ethanol has proven elusive and remains not fully understood.[20][21] Identifyingmolecular targets for ethanol is unusually difficult, in large part due to its unique biochemical properties.[21] Specifically, ethanol is a very lowmolecular weight compound and is of exceptionally lowpotency in its actions, causing effects only at very high (millimolarmM) concentrations.[21][22] For these reasons, it is not possible to employ traditional biochemical techniques to directly assess the binding of ethanol toreceptors orion channels.[21][22] Instead, researchers have had to rely on functional studies to elucidate the actions of ethanol.[21] Even at present, nobinding sites have been unambiguously identified and established for ethanol. Studies have published strong evidence for certain functions of ethanol in specific systems, but other laboratories have found that these findings do not replicate with different neuronal types andheterologously expressed receptors.[23] Thus, there remains lingering doubt about the mechanisms of ethanol listed here, even for the GABAA receptor, the most-studied mechanism.[24]
In the past, alcohol was believed to be a non-specific pharmacological agent affecting manyneurotransmitter systems in the brain,[25] but progress has been made over the last few decades.[26][21] It appears that it affects ion channels, in particularligand-gated ion channels, to mediate its effects in the CNS.[20][26][27][21] In some systems, these effects are facilitatory, and in others inhibitory. Moreover, although it has been established that ethanol modulates ion channels to mediate its effects,[27] ion channels are complex proteins, and their interactions and functions are complicated by diversesubunit compositions and regulation by conserved cellular signals (e.g. signaling lipids).[20][21]
Alcohol is also converted intophosphatidylethanol (PEth, an unnatural lipid metabolite) byphospholipase D2. This metabolite competes withPIP2 agonist sites onlipid-gated ion channels.[28][29] The result of these direct effects is a wave of further indirect effects involving a variety of otherneurotransmitter andneuropeptide systems.[25] This presents a novel indirect mechanism and suggests that a metabolite, not the ethanol itself, could cause the behavioural or symptomatic effects of alcohol intoxication. Many of the primary targets of ethanol are known to bind PIP2 including GABAA receptors,[30] but the role of PEth needs to be investigated further.
List of known actions in the central nervous system
Many of these actions have been found to occur only at very high concentrations that may not be pharmacologically significant at recreational doses of ethanol, and it is unclear how or to what extent each of the individual actions is involved in the effects of ethanol.[21] Some of the actions of ethanol on ligand-gated ion channels, specifically the nicotinic acetylcholine receptors and the glycine receptor, aredose-dependent, with potentiationor inhibition occurring dependent on ethanol concentration.[22] This seems to be because the effects of ethanol on these channels are a summation of positive and negative allosteric modulatory actions.[22]
Ethanol has been found to enhance GABAA receptor-mediated currents in functional assays.[20][21] Ethanol has long shown a similarity in its effects topositive allosteric modulators of the GABAA receptor likebenzodiazepines,barbiturates, and variousgeneral anesthetics.[20][21] Some of these effects includeanxiolytic,anticonvulsant,sedative, andhypnotic effects, cognitive impairment, and motor incoordination.[46] In accordance, it was theorized and widely believed that the primary mechanism of action of ethanol isGABAA receptor positive allosteric modulation.[20][21] However, other ion channels are involved in its effects as well.[26][21] Although ethanol exhibits positiveallosteric binding properties to GABAA receptors, its effects are limited to pentamers containing the δ-subunit rather than the γ-subunit.[21] Ethanol potentiatesextrasynapticδ subunit-containing GABAA receptors at behaviorally relevant (as low as 3 mM) concentrations,[20][21][47] butγ subunit receptors are enhanced only at far higher concentrations (> 100 mM) that are in excess of recreational concentrations (up to 50 mM).[20][21][48]
GABAA receptors containing the δ-subunit have been shown to be located exterior to the synapse and are involved with tonic inhibition rather than its γ-subunit counterpart, which is involved in phasic inhibition.[46] The δ-subunit has been shown to be able to form the allosteric binding site which makes GABAA receptors containing the δ-subunit more sensitive to ethanol concentrations, even to moderate social ethanol consumption levels (30mM).[49] While it has been shown by Santhakumar et al. that GABAA receptors containing the δ-subunit are sensitive to ethanol modulation, depending on subunit combinations receptors could be more or less sensitive to ethanol.[50] It has been shown that GABAA receptors that contain both δ and β3-subunits display increased sensitivity to ethanol.[21] One such receptor that exhibits ethanol insensitivity is α3-β6-δ GABAA.[50] It has also been shown that subunit combination is not the only thing that contributes to ethanol sensitivity. Location of GABAA receptors within the synapse may also contribute to ethanol sensitivity.[46]
Ro15-4513, a closeanalogue of the benzodiazepine antagonistflumazenil (Ro15-1788), has been found to bind to the same site as ethanol and to competitively displace it in a saturable manner.[21][47] In addition, Ro15-4513 blocked the enhancement of δ subunit-containing GABAA receptor currents by ethanolin vitro.[21] In accordance, the drug has been found to reverse many of the behavioral effects of low-to-moderate doses of ethanol in rodents, including its effects on anxiety, memory, motor behavior, and self-administration.[21][47] Taken together, these findings suggest a binding site for ethanol on subpopulations of the GABAA receptor with specific subunit compositions via which it interacts with and potentiates the receptor.[20][21][47][51]
Research indicatesethanol is involved in the inhibition of L-type calcium channels. One study showed the nature of ethanol binding to L-type calcium channels is according to first-order kinetics with aHill coefficient around 1. This indicates ethanol binds independently to the channel, expressingnoncooperative binding.[41] Early studies showed a link between calcium and the release ofvasopressin by thesecondary messenger system.[52] Vasopressin levels are reduced after the ingestion of alcohol.[53] The lower levels of vasopressin from the consumption of alcohol have been linked to ethanol acting as an antagonist to voltage-gated calcium channels (VGCCs). Studies conducted by Treistman et al. in theaplysia confirm inhibition of VGCC by ethanol.Voltage clamp recordings have been done on the aplysia neuron. VGCCs were isolated and calcium current was recorded usingpatch clamp technique having ethanol as a treatment. Recordings were replicated at varying concentrations (0, 10, 25, 50, and 100 mM) at a voltage clamp of +30 mV. Results showed calcium current decreased as concentration of ethanol increased.[54] Similar results have shown to be true in single-channel recordings from isolated nerve terminal of rats that ethanol does in fact block VGCCs.[55]
Studies done by Katsura et al. in 2006 on mouse cerebral cortical neurons, show the effects of prolonged ethanol exposure. Neurons were exposed to sustained ethanol concentrations of 50 mM for 3 daysin vitro.Western blot and protein analysis were conducted to determine the relative amounts of VGCC subunit expression. α1C, α1D, and α2/δ1 subunits showed an increase of expression after sustained ethanol exposure. However, the β4 subunit showed a decrease. Furthermore, α1A, α1B, and α1F subunits did not alter in their relative expression. Thus, sustained ethanol exposure may participate in the development of ethanol dependence in neurons.[56]
Other experiments done by Malysz et al. have looked into ethanol effects on voltage-gated calcium channels ondetrusor smooth muscle cells in guinea pigs. Perforated patch clamp technique was used having intracellular fluid inside the pipette and extracellular fluid in the bath with added 0.3% vol/vol (about 50-mM) ethanol. Ethanol decreased theCa2+ current in DSM cells and induced muscle relaxation. Ethanol inhibits VGCCs and is involved in alcohol-induced relaxation of the urinary bladder.[57]
The reinforcing effects of alcohol consumption are mediated by acetaldehyde generated bycatalase and other oxidizing enzymes such ascytochrome P-4502E1 in the brain.[60] Although acetaldehyde has been associated with some of the adverse and toxic effects of ethanol, it appears to play a central role in the activation of themesolimbic dopamine system.[45]
With chronic alcohol intake, consumption of ethanol similarly induces CREB phosphorylation through the D1 receptor pathway, but it also alters NMDA receptor function through phosphorylation mechanisms;[61][62] an adaptivedownregulation of the D1 receptor pathway and CREB function occurs as well.[61][62] Chronic consumption is also associated with an effect on CREB phosphorylation and function via postsynaptic NMDA receptor signaling cascades through aMAPK/ERK pathway andCAMK-mediated pathway.[62] These modifications to CREB function in the mesolimbic pathwayinduce expression (i.e., increase gene expression) of ΔFosB in theNAcc,[62] where ΔFosB is the "master control protein" that, when overexpressed in the NAcc, isnecessary and sufficient for the development and maintenance of an addictive state (i.e., its overexpression in the nucleus accumbens produces and then directly modulates compulsive alcohol consumption).[62][63][64][65]
Central nervous system depression, anxiety suppression, stress suppression, sedation, nausea, possible vomiting. Impaired motor, memory, cognition and sensory function.
>140
30
>0.14%
Decreased blood flow to brain, slurred speech, double or blurry vision.
300
65
0.3%
Stupefaction, confusion, numbness, dizziness, loss of consciousness.
400
87
0.4%
Ethylic intoxication, drunkenness, inebriation, alcohol poisoning or possible death.
500
109
>0.55%
Unconsciousness, coma and death.
Recreational concentrations of ethanol are typically in the range of 1 to 50 mM.[48][20] Very low concentrations of 1 to 2 mM ethanol produce zero or undetectable effects except in alcohol-naive individuals.[48] Slightly higher levels of 5 to 10 mM, which are associated with light social drinking, produce measurable effects including changes in visual acuity, decreased anxiety, and modest behavioral disinhibition.[48] Further higher levels of 15 to 20 mM result in a degree of sedation and motor incoordination that is contraindicated with the operation of motor vehicles.[48] In jurisdictions in the U.S., maximum blood alcohol levels for legal driving are about 17 to 22 mM.[67][68] In the upper range of recreational ethanol concentrations of 20 to 50 mM, depression of the central nervous system is more marked, with effects including complete drunkenness, profound sedation, amnesia, emesis, hypnosis, and eventually unconsciousness.[48][67] Levels of ethanol above 50 mM are not typically experienced by normal individuals and hence are not usually physiologically relevant; however, such levels – ranging from 50 to 100 mM – may be experienced by alcoholics with high tolerance to ethanol.[48] Concentrations above this range, specifically in the range of 100 to 200 mM, would cause death in all people except alcoholics.[48]
As drinking increases, people become sleepy or fall into astupor. After a very high level of consumption[vague], the respiratory system becomes depressed and the person will stop breathing. Comatose patients may aspirate their vomit (resulting in vomitus in the lungs, which may cause "drowning" and laterpneumonia if survived). CNS depression and impaired motor coordination along with poor judgment increase the likelihood of accidental injury occurring. It is estimated that about one-third of alcohol-related deaths are due to accidents and another 14% are from intentional injury.[69]
In addition to respiratory failure and accidents caused by its effects on the central nervous system, alcohol causes significant metabolic derangements.Hypoglycaemia occurs due to ethanol's inhibition ofgluconeogenesis, especially in children, and may causelactic acidosis,ketoacidosis, andacute kidney injury. Metabolic acidosis is compounded by respiratory failure. Patients may also present with hypothermia.
Thepharmacokinetics of ethanol are well characterized by theADME acronym (absorption, distribution, metabolism, excretion). Besides the dose ingested, factors such as the person'stotal body water, speed of drinking, the drink's nutritional content, and the contents of the stomach all influence the profile ofblood alcohol content (BAC) over time. Breath alcohol content (BrAC) and BAC have similar profile shapes, so most forensic pharmacokinetic calculations can be done with either. Relatively few studies directly compare BrAC and BAC within subjects and characterize the difference in pharmacokinetic parameters. Comparing arterial and venous BAC, arterial BAC is higher during the absorption phase and lower in the postabsorptive declining phase.[13]
All organisms produce alcohol in small amounts by several pathways, primarily throughfatty acid synthesis,[70]glycerolipid metabolism,[71] andbile acid biosynthesis pathways.[72]Fermentation is a biochemical process during which yeast and certain bacteria convert sugars to ethanol, carbon dioxide, as well as other metabolic byproducts.[73][74] The average human digestive system produces approximately 3g of ethanol per day through fermentation of its contents.[75] Such production generally does not have any forensic significance because the ethanol is broken down before significant intoxication ensues. These trace amounts of alcohol range from 0.1 to0.3 μg/mL in the blood of healthy humans, with some measurements as high as 1.6 μg/mL (0.002 g/L).[76]
Auto-brewery syndrome is a condition characterized by significant fermentation of ingested carbohydrates within the body. In rare cases, intoxicating quantities of ethanol may be produced, especially after eating meals. Claims of endogenous fermentation have been attempted as a defense against drunk driving charges, some of which have been successful, but the condition is under-researched.[77]
People drinkingspritzers at a festival in Hungary. Carbonated alcoholic drinks seem to be absorbed faster.
Ethanol is most commonly ingested by mouth,[2] but otherroutes of administration are possible, such asinhalation,enema, or byintravenous injection.[4][78] Withoral administration, the ethanol is absorbed into the portal venous blood through the mucosa of the gastrointestinal tract, such as in the oral cavity, stomach, duodenum, and jejunum.[13] The oralbioavailability of ethanol is quite high, with estimates ranging from 80% at a minimum[2][3] to 94%-96%.[79] The ethanol molecule is small and uncharged, and easily crosses biological membranes by passive diffusion.[80] The absorption rate of ethanol is typically modeled as a first-order kinetic process depending on the concentration gradient and specific membrane. The rate of absorption is fastest in the duodenum and jejunum, owing to the larger absorption surface area provided by the villi and microvilli of the small intestines.Gastric emptying is therefore an important consideration when estimating the overall rate of absorption in most scenarios;[13] the presence of a meal in the stomach delays gastric emptying,[4][78] and absorption of ethanol into the blood is consequently slower.[81] Due to irregular gastric emptying patterns, the rate of absorption of ethanol is unpredictable, varying significantly even between drinking occasions.[13] In experiments, aqueous ethanol solutions have been given intravenously or rectally to avoid this variation.[13] The delay in ethanol absorption caused by food is similar regardless of whether food is consumed just before, at the same time, or just after ingestion of ethanol.[4] The type of food, whetherfat,carbohydrates, orprotein, also is of little importance.[78] Not only does food slow the absorption of ethanol, but it also reduces the bioavailability of ethanol, resulting in lower circulating concentrations.[4]
Regarding inhalation, early experiments with animals showed that it was possible to produce significant BAC levels comparable to those obtained by injection, by forcing the animal to breathe alcohol vapor.[82] In humans, concentrations of ethanol in air above 10 mg/L caused initial coughing and smarting of the eyes and nose, which went away after adaptation. 20 mg/L was just barely tolerable. Concentrations above 30 mg/L caused continuous coughing and tears, and concentrations above 40 mg/L were described as intolerable, suffocating, and impossible to bear for even short periods. Breathing air with concentration of 15 mg/L ethanol for 3 hours resulted in BACs from 0.2 to 4.5 g/L, depending on breathing rate.[83] It is not a particularly efficient or enjoyable method of becoming intoxicated.[4]
Ethanol is not absorbed significantly through intact skin. The steady state flux is0.08 μmol/cm2/hr.[84] Applying a 70% ethanol solution to a skin area of1000 cm2 for 1 hr would result in approximately0.1 g of ethanol being absorbed.[85] The substantially increased levels of ethanol in the blood reported for some experiments are likely due to inadvertent inhalation.[4] A study that did not prevent respiratory uptake found that applying 200 mL of hand disinfectant containing 95% w/w ethanol (150 g ethanol total) over the course of 80 minutes in a 3-minutes-on 5-minutes-off pattern resulted in the median BAC among volunteers peaking 30 minutes after the last application at 17.5 mg/L (0.00175%). This BAC roughly corresponds to drinking one gram of pure ethanol.[86] Ethanol is rapidly absorbed through cut or damaged skin, with reports of ethanol intoxication and fatal poisoning.[87]
The timing of peak blood concentration varies depends on the type of alcoholic drink:[88]
Also, carbonated alcoholic drinks seem to have a shorter onset compare to flat drinks in the same volume. One theory is that carbon dioxide in the bubbles somehow speeds the flow of alcohol into the intestines.[89]
Absorption is reduced by a large meal. Stress speeds up absorption.[81]
After absorption, the alcohol goes through theportal vein to the liver, then through thehepatic veins to the heart, then thepulmonary arteries to the lungs, then thepulmonary veins to the heart again, and then enterssystemic circulation.[13][90] Once in systematic circulation, ethanoldistributes throughout the body,diffusing passively and crossing allbiological membranes including theblood-brain barrier.[2][78] At equilibrium, ethanol is present in all body fluids and tissues in proportion to their water content. Ethanol does notbind to plasma proteins or other biomolecules.[13][2][3] The rate of distribution depends on blood supply,[4] specifically the cross-sectional area of the local capillary bed and the blood flow per gram of tissue.[13] As such, ethanol rapidly affects the brain, liver, andkidneys, which have high blood flow.[2] Other tissues with lower circulation, such as skeletal muscles andbone, require more time for ethanol to distribute into.[4][13] In rats, it takes around 10–15 minutes for tissue and venous blood to reach equilibrium.[91]Peak circulating levels of ethanol are usually reached within a range of 30 to 90 minutes of ingestion, with an average of 45 to 60 minutes.[4][2] People who have fasted overnight have been found to reach peak ethanol concentrations more rapidly, at within 30 minutes of ingestion.[4]
Thevolume of distributionVd contributes about 15% of the uncertainty to Widmark's equation[92] and has been the subject of much research. Widmark originally used units of mass (g/kg) for EBAC, thus he calculated the apparentmass of distributionMd or mass of blood in kilograms. He fitted an equation of the body weightW in kg, finding an average rho-factor of 0.68 for men and 0.55 for women. Thisρm has units of dose per body weight (g/kg) divided by concentration (g/kg) and is therefore dimensionless. However, modern calculations use weight/volume concentrations (g/L) for EBAC, so Widmark's rho-factors must be adjusted for the density of blood, 1.055 g/mL. This has units of dose per body weight (g/kg) divided by concentration (g/L blood) - calculation gives values of 0.64 L/kg for men and 0.52 L/kg for women, lower than the original.[93] Newer studies have updated these values to population-averageρv of 0.71 L/kg for men and 0.58 L/kg for women. But individualVd values may vary significantly - the 95% range forρv is 0.58-0.83 L/kg for males and 0.43-0.73 L/kg for females.[94] A more accurate method for calculatingVd is to usetotal body water (TBW) - experiments have confirmed that alcohol distributes almost exactly in proportion to TBW within the Widmark model.[95] TBW may be calculated usingbody composition analysis or estimated using anthropometric formulas based on age, height, and weight.Vd is then given by, where is the water content of blood, approximately 0.825 w/v for men and 0.838 w/v for women.[96]
These calculations assume Widmark's zero-order model for the effects of metabolization, and assume that TBW is almost exactly the volume of distribution of ethanol. Using a more complex model that accounts for non-linear metabolism, Norberg found that Vd was only 84-87% of TBW.[97] This finding was not reproduced in a newer study which found volumes of distribution similar to those in the literature.[79]
One pathway involvesalcohol dehydrogenase, particularly the IB (class I), beta polypeptide (ADH1B, EC 1.1.1.1) enzyme. The reaction uses NAD+ to convert the ethanol intoacetaldehyde (a toxic carcinogen). The enzymeacetaldehyde dehydrogenase (aldehyde dehydrogenase 2 familyALDH2, EC 1.2.1.3) then converts the acetaldehyde into the non-toxic acetate ion (commonly found inacetic acid or vinegar).[4][6] This ion is in turn is broken down intocarbon dioxide andwater.[4] Specifically, acetate combines withcoenzyme A (acetyl-CoA synthetase) to formacetyl-CoA, via the enzymes acyl-CoA synthetase short-chain family member 2ACSS2 (EC 6.2.1.1) and acetyl-CoA synthase 2 (ACSS1). acetyl-CoA then participates in thecitric acid cycle.[2][98] At even low physiological concentrations, ethanol completely saturates alcohol dehydrogenase.[4] This is because ethanol has high affinity for the enzyme and very high concentrations of ethanol occur when it is used as a recreational substance.[4]
Themicrosomal ethanol-oxidizing system (MEOS), specifically mediated by thecytochrome P450 enzymeCYP2E1, is another major route of ethanol metabolism.[4][6] CYP2E1 is predominantly active at higher concentrations.[2] Repeated or chronic use of ethanol increases the activity of CYP2E1.[4][6]
The activity of ADH and CYP2E1 alone does not appear sufficient to fully explain the increase in ethanol metabolism rate. There may be one or more additional pathways that metabolize as much as 25 to 35% of ethanol at typical concentrations.[3]
The reaction from ethanol tocarbon dioxide andwater proceeds in at least 11 steps in humans. C2H6O (ethanol) is converted to C2H4O (acetaldehyde), then to C2H4O2 (acetic acid), then toacetyl-CoA. Once acetyl-CoA is formed, it is free to enter directly into thecitric acid cycle (TCA) and is converted to 2 CO2 molecules in 8 reactions. The equations:
C2H4O2(acetic acid) + CoA + ATP → Acetyl-CoA + AMP + PPi
TheGibbs free energy is simply calculated from the free energy of formation of the product and reactants.[99][100] If catabolism of alcohol goes all the way to completion, then there is a very exothermic event yielding some1325 kJ/mol of energy. If the reaction stops part way through the metabolic pathways, which happens because acetic acid is excreted in the urine after drinking, then not nearly as much energy can be derived from alcohol, indeed, only215.1 kJ/mol. At the very least, the theoretical limits on energy yield are determined to be−215.1 kJ/mol to−1325.6 kJ/mol. The first with NADH is endothermic, requiring47.2 kJ/mol of alcohol, or about 3 molecules ofadenosine triphosphate (ATP) per molecule of ethanol.[original research?]
Variations in genes influence alcohol metabolism and drinking behavior.[101] Certain amino acid sequences in the enzymes used to oxidize ethanol are conserved (unchanged) going back to the last common ancestor over 3.5bya.[102] Evidence suggests thathumans evolved the ability to metabolize dietary ethanol between 7 and 21 million years ago, in a common ancestor shared withchimpanzees andgorillas but notorangutans.[103] Gene variation in these enzymes can lead to variation in catalytic efficiency between individuals. Some individuals have less effective metabolizing enzymes of ethanol, and can experience more marked symptoms from ethanol consumption than others.[104] However, those having acquiredalcohol tolerance have a greater quantity of these enzymes, and metabolize ethanol more rapidly. Specifically, ethanol has been observed to be cleared more quickly by regular drinkers than non-drinkers.[104]
Falsely high BAC readings may be seen in patients with kidney or liver disease or failure. Such persons also have impaired acetaldehyde dehydrogenase, which causes acetaldehyde levels to peak higher, producing more severehangovers and other effects such as flushing and tachycardia. Conversely, members of certain ethnicities that traditionally did not use alcoholic beverages have lower levels of alcohol dehydrogenases and thus "sober up" very slowly but reach lower aldehyde concentrations and have milder hangovers. The rate of detoxification of alcohol can also be slowed by certain drugs which interfere with the action of alcohol dehydrogenases, notablyaspirin,furfural (which may be found infusel alcohol), fumes ofcertain solvents, manyheavy metals, and somepyrazole compounds. Also suspected of having this effect arecimetidine,ranitidine, andacetaminophen (paracetamol).[citation needed]
An "abnormal" liver with conditions such ashepatitis,cirrhosis,gall bladder disease, andcancer is likely to result in a slower rate of metabolism. People under 25 and women may process alcohol more slowly.[105]
Food such asfructose can increase the rate of alcohol metabolism. The effect can vary significantly from person to person, but a 100 g dose of fructose has been shown to increase alcohol metabolism by an average of 80%. In people with proteinuria and hematuria, fructose can cause falsely high BAC readings, due to kidney-liver metabolism.[106]
During a typical drinking session, approximately 90% of the metabolism of ethanol occurs in the liver.[4][6] Alcohol dehydrogenase and aldehyde dehydrogenase are present at their highest concentrations (in liver mitochondria).[98][107] But these enzymes are widely expressed throughout the body, such as in thestomach andsmall intestine.[2] Some alcohol undergoes a first pass of metabolism in these areas, before it ever enters the bloodstream.[90]
Under alcoholic conditions, the citric acid cycle is stalled by the oversupply of NADH derived from ethanol oxidation. The resulting backup of acetate shifts the reaction equilibrium foracetaldehyde dehydrogenase back towards acetaldehyde. Acetaldehyde subsequently accumulates and begins to form covalent bonds with cellular macromolecules, forming toxic adducts that, eventually, lead to death of the cell.This same excess of NADH from ethanol oxidation causes the liver to move away from fatty acid oxidation, which produces NADH, towards fatty acid synthesis, which consumes NADH. This consequentlipogenesis is believed to account largely for the pathogenesis ofalcoholic fatty liver disease.
In human embryos and fetuses, ethanol is not metabolized via ADH as ADH enzymes are not yet expressed to any significant quantity in human fetal liver (the induction of ADH only starts after birth, and requires years to reach adult levels).[108] Accordingly, the fetal liver cannot metabolize ethanol or other low molecular weight xenobiotics. In fetuses, ethanol is instead metabolized at much slower rates by different enzymes from the cytochrome P-450 superfamily (CYP), in particular by CYP2E1. The low fetal rate of ethanol clearance is responsible for the important observation that the fetal compartment retains high levels of ethanol long after ethanol has been cleared from the maternal circulation by the adult ADH activity in the maternal liver.[109] CYP2E1 expression and activity have been detected in various human fetal tissues after the onset of organogenesis (ca 50 days of gestation).[110] Exposure to ethanol is known to promote further induction of this enzyme in fetal and adult tissues. CYP2E1 is a major contributor to the so-calledMicrosomal Ethanol Oxidizing System (MEOS)[111] and its activity in fetal tissues is thought to contribute significantly to the toxicity of maternal ethanol consumption.[108][112] In presence of ethanol and oxygen, CYP2E1 is known[by whom?] to release superoxide radicals and induce the oxidation of polyunsaturated fatty acids to toxic aldehyde products like 4-hydroxynonenal (HNE).[citation needed]
The concentration of alcohol in breast milk produced during lactation is closely correlated to the individual's blood alcohol content.[113]
Alcohol is removed from the bloodstream by a combination of metabolism, excretion, and evaporation. 90-98% of ingested ethanol is metabolized into carbon dioxide and water.[4] Around 5 to 10% of ethanol that is ingested is excreted unchanged inurine,breath, andsweat.[2] Transdermal alcohol that diffuses through the skin as insensible perspiration or is exuded as sweat (sensible perspiration) can be detected using wearable sensor technology[114] such as SCRAM ankle bracelet[115] or the more discreet ION Wearable.[116] Ethanol or its metabolites may be detectable in urine for up to 96 hours (3–5 days) after ingestion.[2]
Unlike most physiologically active materials, in typical recreational use, ethanol is removed from the bloodstream at an approximately constant rate (linear decay orzero-order kinetics), rather than at a rate proportional to the current concentration (exponential decay with a characteristicelimination half-life).[6][5] This is because typical doses of alcohol saturate the enzymes' capacity. In Widmark's model, the elimination rate from the blood,β, contributes 60% of the uncertainty.[92] Similarly toρ, its value depends on the units used for blood.[93]β varies 58% by occasion and 42% between subjects; it is thus difficult to determineβ precisely, and more practical to use a mean and a range of values. Typical elimination rates range from 10 to 34 mg/dL per hour,[6][4] with Jones recommending the range 0.10 - 0.25 g/L/h for forensic purposes, for all subjects.[117] Earlier studies found mean elimination rates of 15 mg/dL per hour for men and 18 mg/dL per hour for women,[6][4] but Jones found 0.148 g/L/h and 0.156 g/L/h respectively. Although the difference between sexes is statistically significant, it is small compared to the overall uncertainty, so Jones recommends using the value 0.15 for the mean for all subjects.[117] This mean rate is very roughly 8 grams of pureethanol per hour (one Britishunit).[118] Explanations for the gender difference are quite varied and include liver size, secondary effects of the volume of distribution, and sex-specific hormones.[119] A 2023 study using a more complex two-compartment model with M-M elimination kinetics, with data from 60 men and 12 women, found statistically small effects of gender on maximal elimination rate and excluded them from the final model.[79]
At concentrations below 0.15-0.20 g/L, alcohol is eliminated more slowly and the elimination rate more closely follows first-order kinetics. The overall behavior of the elimination rate is described well byMichaelis–Menten kinetics. This change in behavior was not noticed by Widmark because he could not analyze low BAC levels.[93] The rate of elimination of ethanol is also increased at very high concentrations, such as in overdose, again more closely followingfirst-order kinetics, with an elimination half-life of about 4 or 4.5 hours (a clearance rate of approximately 6 L/hour/70 kg). This is thought to be due to increased activity of CYP2E1.[3][2]
Eating food in proximity to drinking increases elimination rate significantly, mainly due to increased metabolism.[79]
In fasting volunteers, blood levels of ethanol increase proportionally with the dose of ethanol administered.[78] Peak blood alcohol concentrations may be estimated by dividing the amount of ethanol ingested by thebody weight of the individual and correcting for water dilution.[4] For time-dependent calculations, Swedish professor Erik Widmark developed a model of alcohol pharmacokinetics in the 1920s.[120] The model corresponds to a single-compartment model with instantaneous absorption andzero-order kinetics for elimination. The model is most accurate when used to estimate BAC a few hours after drinking a single dose of alcohol in a fasted state, and can be within 20%CV of the true value.[121][122] It is less accurate for BAC levels below 0.2 g/L (alcohol is not eliminated as quickly as predicted) and consumption with food (overestimating the peak BAC and time to return to zero).[123][93]
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