Black stools from bismuth are expected
The client is on day 6 of bismuth quadruple therapy for Helicobacter pylori and has had black stools since day 2. Bismuth reacts with sulfur in the bowel to form bismuth sulfide, which turns the stool black and may darken the tongue. Formed, non-sticky, odorless black stools with stable vital signs are a harmless drug effect, so he should finish the full course.
Distinguishing bismuth stools from melena
The nurse must still rule out bleeding, because an ulcer can bleed. Melena, black stool from upper gastrointestinal bleeding, is typically tarry, sticky, and foul-smelling because digested blood changes its texture and odor. It is often accompanied by signs of blood loss such as dizziness, tachycardia, pallor, or weakness. This client's stools are formed, not sticky, and without a foul odor; his pulse is 76/min, and he has no dizziness or abdominal pain.
| Feature | Bismuth stools | Melena |
|---|
| Color | Black | Black |
| Consistency | Formed | Tarry and sticky |
| Odor | Not foul | Foul |
| Associated signs | None | Dizziness, tachycardia, pallor |
| Action | Reassure; complete therapy | Urgent evaluation |
Why the other conclusions are wrong
Slow upper GI bleeding would show the features of melena or signs of anemia, which he does not have. Metronidazole, part of the regimen, causes a metallic taste and a disulfiram-like reaction with alcohol, not black stools, so there is no reason to stop it. Watch out! Stool color does not indicate antibiotic resistance; eradication is confirmed with a urea breath test or stool antigen test after treatment is completed, as directed by the prescriber.
Why completing the course matters
Stopping H. pylori therapy early because of an expected effect leads to treatment failure and promotes antibiotic resistance, making future treatment harder. The nurse reassures him, reinforces taking all medicines as prescribed for the full 14-day course, reminds him to avoid alcohol while taking metronidazole, and teaches him to call if stools become tarry, sticky, or foul-smelling, or if he develops dizziness, fainting, vomiting of blood, or severe abdominal pain.
Exam takeaway
Key point! Bismuth causes harmless black stools. Melena is tarry, sticky, foul-smelling, and often comes with signs of blood loss. If the stool is formed and the client is stable, reassure and continue the full course.