Final answer:
Metronidazole should not be combined with alcohol due to the risk of central nervous system toxicity and disulfiram-like reactions, which can cause unpleasant symptoms and pose a health risk.
Step-by-step explanation:
Metronidazole is contraindicated with alcohol because of CNS toxicity and disulfiram reactions. Metronidazole is an antimicrobial medication used to treat a variety of infections caused by bacteria and protozoa. These infections include those caused by Giardia lamblia, Entamoeba histolytica, and Trichomonas vaginalis.
Metronidazole works by interrupting DNA synthesis in these organisms, leading to their death. However, in humans, the combination of metronidazole and alcohol can result in increased central nervous system toxicity due to the similar pathways they affect in the body, which can be dangerous.