A 44-year-old male with severe alcohol use disorder has been maintained on disulfiram 250 mg daily for four months as part of a comprehensive treatment program. He reports strict abstinence until two days ago when he consumed three beers at a social gathering. Within 15 minutes of his first drink, he experienced severe facial flushing, throbbing headache, nausea, profuse vomiting, diaphoresis, chest tightness, and palpitations. He presents to the clinic the following day to discuss the experience. Which of the following best explains the biochemical mechanism responsible for this aversive reaction?