Q. What type of kinetics applies for alcohol in the body? Also, explain the clinical significance of this.

Ethanol or alcohol metabolism follow zero-order kinetics. This means, that a constant amount alcohol is metabolised per unit of time. By increasing the amount of alcohol, the metabolism rate will still remain constant. This means that an increase in alcohol consumption would not mean an increase in the rate of its metabolism. The body will continue to metabolize the alcohol at a constant rate. The accumulation of acetaldehyde in the body is what leads to individuals becoming intoxicated or drunk.

Q. Give a brief summary of the metabolic pathways of ethanol metabolism.

Alcohol is metabolised by 2 major systems in the liver: Alcohol dehydrogenase (ADH) system and the Microsomal Ethanol-Oxidizing system (MEOS).

Alcohol dehydrogenase system is responsible for metabolising low to moderate levels of alcohol. The primary pathway for alcohol metabolism involves alcohol dehydrogenase, about 80- 90%. These enzymes are located mainly in the liver (small amounts found in brain & stomach). These alcohol dehydrogenases are cytosolic enzymes in the liver that catalyze the conversion of ethanol (alcohol) to acetaldehyde, NADH and H⁺ ion. 

MEOS is induced during chronic alcohol consumption (high concentrations of alcohol). This enzyme system, also known as the mixed function oxidase system, uses NADPH as a cofactor in metabolism of ethanol. In this enzyme system alcohol is converted to acetaldehyde.

Acetaldehyde dehydrogenase converts the acetaldehyde into acetate, a non-toxic metabolite.

Q. Which drugs can affect this metabolism and what are the effects thereof?

Drugs that affect the metabolism of alcohol include: disulfiram, metronidazole, cephalosporins and hypoglycaemics. These drugs inhibit the enzyme aldehyde dehydrogenase, thus acetaldehyde cannot be converted into the non-toxic metabolite acetate. 

This causes acetaldehyde to accumulate causing an unpleasant reaction of:

• • Facial flushing
  • Nausea
  • Vomiting
  • Dizziness
  • Headaches

​​​​​​​Ex. Disulfiram is used to deter drinking by patients with alcohol dependence.