Three days after completing a 5‑day course of cefuroxime and metronidazole, I have had one episode of loose stool and now have progressive fatigue, dysgeusia (bitter taste), nausea, and mild gastroesophageal reflux—are these residual antibiotic effects or a new problem, and if new, what could it be?

Post-Antibiotic Symptoms: Likely Metronidazole-Related Effects

Your symptoms of progressive fatigue, bitter metallic taste, nausea, and gastric reflux three days after completing cefuroxime and metronidazole are most likely residual effects from metronidazole, which commonly causes these specific adverse reactions and can persist for several days after discontinuation.

Understanding Metronidazole's Adverse Effect Profile

The constellation of symptoms you describe—particularly the bitter taste, nausea, and fatigue—are classic metronidazole side effects documented in FDA labeling:

• Metallic taste is explicitly noted as "not unusual" and described as "a sharp, unpleasant metallic taste" in the FDA drug label for metronidazole 1
• Gastrointestinal symptoms including nausea (reported by approximately 12% of patients), epigastric distress, and abdominal discomfort are among the most common adverse reactions to metronidazole 1
• Neuropsychiatric effects including weakness and fatigue can occur with metronidazole, particularly as the drug accumulates in tissues 2

Timeline and Resolution

Your symptoms appearing 3 days post-treatment align with metronidazole's pharmacokinetics:

• Metronidazole's neuropsychiatric and gastrointestinal effects typically resolve within 24-48 hours after discontinuation, though some patients experience symptoms for several days 2
• The single episode of loose stool you experienced is consistent with antibiotic-associated diarrhea, which is common with both cefuroxime and metronidazole 3, 1

When to Suspect a New Problem

You should seek immediate medical attention if:

• Diarrhea returns and becomes watery or bloody, especially with fever or abdominal cramps—this could indicate Clostridioides difficile infection (CDI), which can develop "even as late as 2 or more months after having taken the last dose of the antibiotic" 4
• Neurologic symptoms worsen or new symptoms develop (numbness, tingling, seizures)—metronidazole can cause peripheral neuropathy that requires immediate drug discontinuation 1
• Symptoms persist beyond 5-7 days from your last antibiotic dose
• You develop high fever (>38.5°C), severe abdominal pain, or signs of dehydration 3

Critical Pitfall: C. difficile Infection

While your current symptoms favor residual drug effects, remain vigilant for CDI:

• Both metronidazole and cefuroxime can trigger CDI 3
• CDI typically presents with watery diarrhea (≥3 unformed stools in 24 hours), but can initially manifest with nonspecific symptoms 3
• If diarrhea recurs or worsens, contact your physician immediately for stool toxin testing 3

Expected Recovery Pattern

Most patients experience complete resolution of metronidazole-related symptoms within 3-7 days of discontinuation 2. Your progressive fatigue during the day and persistent bitter taste should gradually improve over the next few days. The mild reflux may be managed with over-the-counter antacids if needed.

Monitoring Recommendations

• Track symptom progression daily—improvement should be evident within 48-72 hours
• Maintain adequate hydration and nutrition despite nausea
• Avoid alcohol completely, as metronidazole can cause a disulfiram-like reaction even days after discontinuation 1
• If symptoms plateau or worsen after 5 days total from your last dose, medical evaluation is warranted