Ethanol derives from the fermentation of naturally occurring sugars. The International Union of Pure and Applied Chemistry (IUPAC) nomenclature for the chemical compound ethanol is a structural composition consisting of a pair of carbon atoms with an alkyl group coupled with an -OH functional group; the -OH group makes it chemically an alcohol. Ethanol, unlike methanol, butanol, propanol, etc., can be consumed by humans without dying in its purest form.
Ethanol's uses include:
1. Ethanol in lieu of fomepizole in methanol poisoning 
2. Ethanol in lieu of fomepizole in ethylene glycol poisoning 
3. As a hand sanitizer for the prevention of healthcare-associated infections (HCAI) 
4. Ethanol lock therapy for reducing the incidence of bloodstream infections acquired through IV catheters 
Ethanol as an embolic, sclerosing and an ablative agent: 
1. As an ablative agent in hypertrophic obstructive cardiomyopathy by controlled septal infarction 
2. As an embolic agent for embolization of arteriovenous malformations 
3. As a sclerosing agent to reduce pain in musculoskeletal hemangiomas, as an alternative to surgery or to reduce the morbidity associated with the tumor resection 
4. As a sclerosant for lymphatic malformations occurring in the neck and the mediastinum under the guidance of CT 
5. As a sclerosing agent in the treatment of symptomatic simple renal cysts 
6. As an ablative agent against thyroid cystic nodules 
7. As an ablative agent in endoscopic ultrasound (EUS) guided ablation of a single insulinoma 
8. As an ablative agent for hepatocellular carcinomas 
9. Ethanol injected peripherally in abetting pain in trigeminal neuralgia 
10. For neurolysis of brachial plexus pain associated with cancers 
11. For neurolysis of splanchnic nerve to decrease cancer-associated upper abdominal pain 
As an antidote for:
As a hand sanitizer and preventing sepsis:
As an ablative/sclerosing/embolic agent:
For methanol and ethylene glycol poisoning, ethanol administration can be either through an IV line, a nasogastric tube, or even orally. Still, an IV ethanol infusion is always preferable to other routes. A plasma concentration of methanol exceeding 20 mg/dL is a reference for starting ethanol therapy.
Commercially available, 10% ethanol solution dosing is as follows:
This regimen can occur in an intensive care setting with the plasma concentrations of alcohol requiring hourly monitoring until reaching a desired plasma ethanol concentration of 100 mg/dL, following which the plasma sampling frequency is reducible to 2 to 4 hours. One must keep in mind that the FDA approved IV fomepizole for methanol/ethylene glycol poisoning, and it is a specific inhibitor of ADH. It has a far superior affinity for ADH than ethanol. Even though fomepizole is a superior antidote in comparison to ethanol, the availability and the limited knowledge of fomepizole has resulted in the continuance of ethanol infusions as a treatment in these cases.
Alcohol-based hand sanitizers (ABHS) are time-proven weapons for preventing nosocomial infections. However, the efficacy of the same against neutralizing microorganisms rests on the effectiveness of its use. Several studies dedicated to establishing complete disinfection on the surface of the hands have concluded that an amount of 2.4 to 3 mL is the recommendation with an application time of minimum 25 to 30 seconds to establish maximum disinfection.
Ethanol lock therapy (ELT) uses 70% ethanol over a minimum of 4 hours, reaching a maximum of 6 hours in conjunction with the regular antibiotic therapy has significantly brought down the rate of catheter-related bloodstream infection (CRBSI). This therapy is especially useful when there have been no reports of bacterias being resistant to ethanol.
Ethanol, as a chemical ablative/sclerosing agent, has been put to use rigorously, in treating varying neoplasms, cysts, vascular malformations, and even chemical neurolysis. Ethanol is injected into the parenchyma/lesion of the specific organ. It can utilize the guidance of endoscopic ultrasound, or in some cases, the injection can be under CT guidance.
When ethanol converts to acetaldehyde, NAD+ reduces to NADH. NAD+ serves as an electron carrier and donates 2 electrons in this reaction. This reaction increases the NADH/NAD+ ratio in the hepatocytes. This increase in ratio causes:
Ketoacidosis: Via inhibition of the citric acid (TCA) cycle, thereby increasing the levels of acetyl-CoA. This increased acetyl-CoA is shunted into the ketogenesis pathway resulting in ketoacidosis.
Fasting hypoglycemia: The increased ratio inhibits the conversion of malate to oxaloacetate (OAA). This inhibition changes the reaction equilibrium by starting to convert OAA back to malate, impairing gluconeogenesis because the meager amount of OAA is left to convert to phosphoenolpyruvate (PEP) for gluconeogenesis.
Hepatic steatosis: The increased NADH/NAD+ ratio increases the synthesis of fatty acid and glycerol-3-phosphate, thereby increasing the levels of TAGs resulting in fatty liver.
Ingested ethanol mainly metabolizes in the liver; hence hepatic damage is profoundly seen in chronic alcoholism. This damage includes steatosis, cirrhosis, and hepatic carcinoma. Other organs/organ systems involved are:
In cases of methanol/ethylene glycol toxicity:
The loading and the maintenance dose should be carefully monitored in an intensive care setting to prevent the patient from any toxic manifestation of the antidote-ethanol itself. Furthermore, ethanol must not be administered concurrently with fomepizole as the later will inhibit the metabolism of ethanol in the same way as it inhibits the metabolism of methanol/ethylene glycol. This inhibition will result in an exaggerated rise in ethanol level in the body as its half-life is now prolonged, and will inadvertently result in the manifestation of the intoxicating nature of ethanol. Contraindications to ethanol also include pregnancy and breastfeeding.
Though there is no clearcut contraindication in any particular medical setup, it has been well established that ABHS doesn't kill the spores of several microorganisms, including the likes of Clostridium difficile. It is also not effective against certain protozoan oocysts, for example, cryptosporidium. ABHS has also been inefficient against a certain non-enveloped virus-like Norovirus.
As an Ablative Agent:
Percutaneous ethanol injection is contraindicated when:
Ethanol follows zero-order kinetics. Alcohol absorption occurs mostly in the proximal part of the small intestine, but a little fraction is also absorbed by the mucosal layer of the mouth, esophagus, and stomach. Alcohol metabolism mostly takes place in the liver, with a rate of oxidation per unit time yielding a linear curve. Physiological conditions like starvation lower the rate of metabolism of ethanol, whereas insulin enhances it. Alcohol metabolism occurs via an oxidative and non-oxidative pathway. Various enzymes play a role in the oxidative pathway. They are alcohol dehydrogenase (ADH) (present in the cytosol), aldehyde dehydrogenase (ALDH) (present in mitochondria), cytochrome P450 (CYP2E1) (present in microsomes) and catalase (present in peroxisomes). The non-oxidative pathway includes the enzymes, fatty acid ethyl ester synthase (FAEES) and phospholipase D (PLD). Both of these pathways are interrelated since drugs inhibiting the enzymes in the oxidative pathway drives the metabolism through the non-oxidative pathway.
In the oxidative pathway, ethanol is first converted to acetaldehyde by alcohol dehydrogenase (ADH), present in the cytosol. NAD+ serves as an electron carrier for this reaction and gets reduced to NADH. This process significantly reduces hepatic cytosol, paving the way for the hepatocytes damage by reactive oxygen species (ROS) and other byproducts of alcohol metabolism. The drug fomepizole competitively inhibits ADH, thereby preventing the formation of toxic metabolites.
Acetaldehyde is further oxidized by acetaldehyde dehydrogenase to acetone. Acetone finally oxidizes to CO2 in the heart muscle, skeletal muscles, and the brain. Interestingly, a drug called disulfiram competitively inhibits acetaldehyde dehydrogenase, thereby delaying the clearance of acetaldehyde, causing dire symptoms like nausea, vomiting, chest and abdominal pain, dizziness, and worsening hangover. This mechanism of the drug has an application in treating alcohol use disorders. Several drugs exhibit the same property as disulfiram. They are metronidazole, sulfamethoxazole and trimethoprim, chloramphenicol, quinacrine, first-generation sulfonylureas, griseofulvin, and some cephalosporins like cefotetan and cefoperazone.
The non-oxidative pathway involves the formation of fatty acid ethyl esters (FAEE) and phosphatidyl ethanol in the end. FAEE causes tissue damage wherein phosphatidyl ethanol forms at the expense of depleting phospholipase D (PLD), which participates in cell signaling.
Alcohol intoxication results in CNS depression by enhancing the effect of GABA, an inhibitory neurotransmitter, on its receptors. It also inhibits the actions of 'glutamate' on the NMDA receptors, resulting in an incautious and dull state of mind. Intoxication by ethanol also gives rise to slurred speech, stupor, and gait abnormalities and may even result in a coma. Clinicians should correct thiamine deficiency, which can accompany chronic alcohol misuse, by supplementing B1. Electrolyte imbalance should be appropriately corrected through infusions. Extensive sympathetic counseling is essential for alcohol abuse. Some drugs focused on promoting alcohol cessation include 'naltrexone' (via antagonism of mu-opioid receptors), disulfiram (via creating negative conditioning through pathways mentioned above), topiramate, and gabapentin.
Alcohol withdrawal is another common morbidity which arises as a sequela to alcohol use disorder (AUD). It results from the abrupt cessation of alcohol consumption after binge drinking or long term dependence. The signs and symptoms usually arise by 6 to 24 hours of stopping alcohol consumption. It may range from milder symptoms like anxiety, headache, palpitations to severe symptoms like withdrawal seizures, and delirium tremens. The treatment should focus on providing supportive therapy for all the complaints. Any associated comorbidities should have therapy with a 'banana bag' therapy of essential vitamins. The severe symptoms require the use of benzodiazepines.
Ethanol has existed almost from the start of civilization as a drink for merriment, and only in the recent century, through extensive research, have we been able to use ethanol into treating diseases. Ethanol, as a constituent of hand sanitizers in a medical setup, has emerged to be indispensable in impeding hospital-acquired infections and practitioners to the patient and vice versa transfer of microorganisms. It is the duty of the care provider, including the clinician, nurse, pharmacists, and anyone involved in the overall case management, to ensure that they sanitize their hands, wear gloves before approaching and handling the patient, catheters, tubes, cannulas, etc. The same principle is necessary for choosing an ethanol lock therapy in an ICU setting to prevent sepsis associated with infected catheters.
Ethanol, as an ablative, is under ongoing research for different neoplastic conditions where surgery is not feasible. The surgeon must identify such patients by their age, financial status, and the patient's comorbid conditions to prefer an ethanol ablation over a classic surgery to prevent mortality. Ethanol, as an antidote to methanol or ethylene glycol poisoning, has been in use for decades now. Even though fomepizole has emerged to be a better drug due to reasons including, but not limited to, better neutralization of the offending agent, predictable pharmacokinetics, and decreased mortality, ethanol is still preferred by many owing to its low cost and greater physician familiarity.
Alcohol use disorder remains a global challenge in consideration of the mortality that correlates with misusing. More than 135 million people, age 12 and older in the USA, actively use alcohol. The clinician must identify such patients and counsel them, and if need be, they should be hospitalized and receive appropriate treatment.
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