Type of kinetics for alcohol in the body:

Alcohol is a small water-soluble molecule that has fast absorption and distribution in the body. Peak levels in the blood can be seen within 30minutes after consumption of alcohol, during a fasting blood test. 90% of alcohol is metabolised by the liver and the rest is metabolised by the lungs and kidneys. Alcohol can be metabolised in 3 ways, namely alcohol dehydrogenase system, microsomal ethanol-oxidizing system and acetaldehyde metabolism.

Summary of the metabolic pathways:

Alcohol can follow any of the 3 paths. The first pathway is alcohol dehydrogenase pathway and it involves alcohol dehydrogenase (ADH), which is a cytosolic enzyme that catalyses the conversion of alcohol to acetaldehyde. These enzymes are mainly located in the liver and small amounts in other organs. Some metabolism occurs in the stomach already, but only in people whom have lower levels of gastric enzymes. H+ is transferred from the ethanol to co-factor NAD+ (nicotinamide adenine dinucleotide).

The next pathway is the microsomal Ethanol-Oxidising System (MEOS), which is also known as the mixed function oxidase system. It makes use of NADPH as a cofactor in the metabolism of ethanol and consists primarily of cytochrome P450 2E1,1A2 and 3A4. During alcohol consumption, MEOS activity is induced. Ethanol metabolism is induced and the clearance of other drugs by the liver.

The third pathway is the acetaldehyde metabolism. Much of the acetaldehyde formed is oxidised in the liver and this reaction is catalysed by mitochondrial NAD-dependent aldehyde dehydrogenase. The products of this reaction is acetate, which is further metabolised to carbon dioxide and water, or it is used to form acetyl-CoA

Drugs that affect metabolism and the effect thereof:

Most drugs have reactions with alcohol; therefore, it is better to actually not consume alcohol while using medications. Fomepizole inhibits alcohol dehydrogenase. This inhibits the conversion of alcohol to acetaldehyde, consequently increase the alcohol levels.

Disulfiram inhibits the oxidation of acetaldehyde, which result in the accumulation of acetaldehyde which causes flushed skin, nausea, vomiting, dizziness and headaches. Metronidazole, Cephalosporins and Hypoglycaemic drugs inhibit aldehyde dehydrogenase which cause effects similar to those of Disulfiram.