A 56-year-old alcoholic male consumes a six-pack of beer before going to bed. After being absorbed from his gut, blood carries the alcohol through the portal vein into the liver where it can be metabolized. Phase I metabolism of ethanol is carried out by cytochrome P450 2E1. Which of the following is true of phase I metabolism? * (A) Always precedes phase II metabolism (B) Are carried out largely in the plasma (C) Examples are oxidation and reduction reactions (D) Includes such reactions as glucuronidation and sulfation (E) Produces very polar metabolites

The correct answer is (C) Examples are oxidation and reduction reactions. Phase I metabolism involves chemical reactions such as oxidation, reduction, and hydrolysis. In the case of alcohol metabolism, the enzyme cytochrome P450 2E1 oxidizes ethanol to acetaldehyde, which is a toxic metabolite and a known carcinogen. This is an example of an oxidation reaction, which is a type of Phase I reaction.

The correct answer is (C) Examples are oxidation and reduction reactions. Phase I metabolism involves chemical reactions such as oxidation (most common), reduction and hydrolysis. Most of these reactions are carried out by the cytochrome P450 group of enzymes. These reactions result in increased polarity of the drug and often involve a functional group being added or uncovered, which will serve as the site of phase II reactions.