A 35-year-old client is being discharged on metronidazole 500 mg PO three times daily for bacterial vaginosis. Which client teaching is most important?

Metronidazole is used for anaerobic infections, bacterial vaginosis, trichomoniasis, C. difficile (oral vancomycin or fidaxomicin now preferred for CDI), Helicobacter pylori, intra-abdominal and pelvic infections, and giardiasis. Key teaching: (1) disulfiram-like reaction with alcohol — even small amounts in mouthwash, cough syrup, or food cooked with wine can cause flushing, severe nausea and vomiting, headache, palpitations, hypotension, dyspnea, and rarely fatal arrhythmia; avoid alcohol during therapy and for at least 48 hours after the last dose (some sources extend to 72 hours); educate patient and family thoroughly; (2) common side effects — metallic taste, nausea, GI upset, dry mouth, dark or reddish-brown urine (harmless from drug metabolites but report any change to ensure no other cause); (3) CNS — dizziness, headache, peripheral neuropathy with prolonged use, rarely seizures or aseptic meningitis; (4) drug interactions — warfarin (INR up), lithium (toxicity), phenytoin, busulfan; (5) avoid in first trimester pregnancy when possible; (6) complete the full course on schedule. Drinking alcohol, mixing with vodka, and stopping for dark urine are unsafe.

No alcohol with metronidazole, including 48 hours after the last dose. Disulfiram-like reaction is the high-yield NCLEX answer. Dark urine is harmless.