When ethanol is metabolized, which compound is produced first?

Ethanol metabolism primarily occurs in the liver through a well-established pathway that consists of two main steps. The first step involves the conversion of ethanol into acetaldehyde, catalyzed by the enzyme alcohol dehydrogenase (ADH). This step is crucial as acetaldehyde is a highly reactive and toxic compound that can contribute to many of the harmful effects associated with ethanol consumption.

Following this initial conversion, acetaldehyde is further metabolized into acetic acid by another enzyme, aldehyde dehydrogenase (ALDH). This second step is essential for detoxifying acetaldehyde, which is necessary to mitigate potential cellular damage.

The other compounds listed, such as formic acid and ethylene glycol, are not direct products of ethanol metabolism. They are associated with the metabolism of other substances (formic acid with methanol, and ethylene glycol is a completely different compound) and do not arise from ethanol metabolism. Therefore, the answer is acetaldehyde, as it is the immediate product formed when ethanol is metabolized.