Amoxicillin × Metronidazole

There is no interaction that calls for action. Amoxicillin and metronidazole are cleared by different routes, share no relevant transporters, and the interaction sections of their labels do not pit them against each other. The combination is prescribed on purpose in more than one setting: Helicobacter pylori eradication, odontogenic infection and abscess, mixed intra-abdominal and pelvic infection, where amoxicillin covers aerobes and metronidazole anaerobes.

What shows up with this pair are each drug's own effects, mostly gastrointestinal: nausea, metallic taste and diarrhoea. Watery diarrhoea starting during the course or weeks later calls for ruling out Clostridioides difficile infection, a risk that belongs to antibiotics in general.

The regimen runs as prescribed, for the intended duration. What does matter is alcohol: the metronidazole label asks for alcoholic drinks to be avoided during treatment because of a disulfiram-like effect with dizziness and vomiting, and that warning holds for a few days after the course. The rest of the regimen depends on the indication: in H. pylori eradication the third component is a proton pump inhibitor or bismuth.