A 45-year-old woman has been admitted to a substance abuse center for her alcoholism. As a first attempt to curb the patient's drinking, she is given a drug that will lead to an elevation of which one of the following metabolites if she drinks alcohol?

One treatment for chronic alcoholism is to inhibit the enzyme aldehyde dehydrogenase, which would lead to the accumulation of acetaldehyde if ethanol has been imbibed. Ethanol metabolism, at the first step, converts ethanol to acetaldehyde (the enzyme is alcohol dehydrogenase). Aldehyde dehydrogenase then converts the acetaldehyde to acetic acid, which is eventually converted to acetylCoA. The accumulation of acetaldehyde initiates the symptoms associated with a hangover, such as headache and nausea. The theory behind the treatment is that, if the individual drinks alcohol while on the drug, the buildup of acetaldehyde will make the person feel very uncomfortable and will lead to a reduction, or cessation, of drinking alcohol. Inhibiting aldehyde dehydrogenase will not lead to elevations of acetic acid, ethanol, carbon dioxide, or carbon monoxide.