BISMUTH SUBSALICYLATE, METRONIDAZOLE AND TETRACYCLINE HYDROCHLORIDE
Clinical safety rating: avoid
Antacids and calcium supplements decrease absorption Can cause photosensitivity and tooth discoloration in children.
Bismuth subsalicylate exerts antimicrobial and anti-inflammatory effects via binding to gastrointestinal mucosa and inhibiting prostaglandin synthesis; metronidazole inhibits DNA synthesis by forming nitro radical anions; tetracycline inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit.
| Metabolism | Bismuth subsalicylate is hydrolyzed in the gut to bismuth and salicylate; salicylate undergoes hepatic glucuronidation and oxidation. Metronidazole is hepatically metabolized via oxidation and glucuronidation (CYP450 enzymes). Tetracycline is primarily excreted unchanged in urine and feces; limited hepatic metabolism. |
| Excretion | Bismuth subsalicylate: Renal excretion of salicylate and bismuth (bismuth largely fecal as insoluble sulfide); Metronidazole: Renal 60–80% (unchanged and metabolites), fecal 6–15%; Tetracycline HCl: Renal 60% unchanged, fecal 40% (biliary and direct excretion). |
| Half-life | Bismuth subsalicylate: Bismuth component ~5 days (accumulation risk), salicylate 2–3 hours; Metronidazole: 8 hours (increased in hepatic impairment); Tetracycline HCl: 6–12 hours (prolonged in renal impairment). |
| Protein binding | Bismuth subsalicylate: Bismuth >90% bound to plasma proteins; Metronidazole: <20%; Tetracycline HCl: 20–60% (mainly albumin). |
| Volume of Distribution | Bismuth subsalicylate: Bismuth 0.3–0.5 L/kg (bone, kidney); Metronidazole: 0.6–1.1 L/kg (wide tissue distribution); Tetracycline HCl: 1.3–1.7 L/kg (bone, teeth). |
| Bioavailability | Oral: Bismuth subsalicylate: Bismuth absorption <1%, salicylate ~90%; Metronidazole: 80–100%; Tetracycline HCl: 70–80% (decreased by food/dairy). |
| Onset of Action | Oral: Bismuth subsalicylate (antidiarrheal) 1–2 hours; Metronidazole (antibacterial) 2–4 hours; Tetracycline HCl (antibacterial) 2–4 hours. |
| Duration of Action | Bismuth subsalicylate: 3–4 hours; Metronidazole: 12–24 hours; Tetracycline: 6–12 hours. Clinical effect duration 10–14 days for H. pylori eradication. |
| Molecular Weight | Bismuth subsalicylate: 362.1 Da; Metronidazole: 171.15 Da; Tetracycline hydrochloride: 480.9 Da |
Each dose consists of 2 capsules (each containing bismuth subsalicylate 262.4 mg, metronidazole 250 mg, and tetracycline hydrochloride 375 mg) taken orally 3 times daily (after meals) for 10 days.
| Dosage form | TABLET, CHEWABLE, TABLET, CAPSULE |
| Renal impairment | For GFR 10-50 mL/min: use with caution and monitor renal function; for GFR <10 mL/min: contraindicated due to tetracycline accumulation. |
| Liver impairment | Child-Pugh A: no adjustment; Child-Pugh B: reduce metronidazole dose by 50%; Child-Pugh C: contraindicated. |
| Pediatric use | Not recommended for children less than 8 years old due to tetracycline-induced permanent tooth discoloration and bone growth inhibition. For children ≥8 years: weight-based dosing not established; use only if benefits outweigh risks and under specialist guidance. |
| Geriatric use | Use with caution; monitor renal function as tetracycline clearance decreases with age; consider dose reduction or alternative therapy in patients with renal impairment. |
| 1st trimester | Avoid: Tetracycline causes fetal bone and tooth discoloration, and metronidazole is associated with cleft palate in animal studies. Bismuth subsalicylate contains salicylate linked to Reye syndrome and bleeding risks. |
| 2nd trimester | Avoid: Tetracycline crosses placenta and deposits in fetal bones/teeth; metronidazole is carcinogenic in some animal studies; salicylate risks persist. |
| 3rd trimester | Avoid: Tetracycline contraindicated in pregnancy (bone/tooth toxicity); metronidazole use in third trimester not recommended; salicylate may cause premature closure of ductus arteriosus and oligohydramnios. |
Clinical note
Antacids and calcium supplements decrease absorption Can cause photosensitivity and tooth discoloration in children.
| FDA category | Positive |
| Placental transfer | All components cross the placenta. Tetracycline accumulates in fetal bone and teeth. Metronidazole reaches fetal plasma levels 30-100% of maternal levels. Salicylate from bismuth subsalicylate crosses and may cause premature ductus closure. |
■ FDA Black Box Warning
Tetracycline should not be used during tooth development (last half of pregnancy, infancy, and childhood to age 8 years) because it may cause permanent yellow-gray-brown discoloration of teeth and enamel hypoplasia. Metronidazole has been shown to be carcinogenic in mice and rats.
| Common Effects | acne |
| Serious Effects |
PregnancyBreastfeedingChildren under 12 years (aspirin/Reye syndrome risk with bismuth subsalicylate)Hypersensitivity to any componentHistory of optic neuritis or peripheral neuropathy (metronidazole)Severe hepatic impairment (metronidazole, tetracycline)
| Precautions | May cause pseudomembranous colitis; avoid alcohol during metronidazole therapy (risk of disulfiram-like reaction); tetracycline may increase intracranial pressure; use caution in hepatic impairment; prolonged use may result in bacterial or fungal superinfection. |
| Food/Dietary |
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| Breastfeeding | Tetracycline is excreted into breast milk in low concentrations but may cause dental staining and bone growth suppression in nursing infants. Metronidazole is excreted in breast milk and may cause diarrhea or candidiasis. Bismuth subsalicylate is excreted as salicylate, which may increase bleeding risk. Use is not recommended during breastfeeding. |
| Lactation Rating | L4 (Hazardous) |
| Teratogenic Risk | First trimester: Tetracycline is associated with inhibition of bone growth and discoloration of deciduous teeth if used after 16 weeks; metronidazole has shown teratogenic effects in animal studies, but human data are conflicting; bismuth subsalicylate is generally avoided due to salicylate's association with fetal harm. Second trimester: Tetracycline risk persists for teeth and bones; metronidazole is generally avoided due to potential neurodevelopmental risks; bismuth subsalicylate is contraindicated due to salicylate effects. Third trimester: Tetracycline may cause skeletal abnormalities; metronidazole is contraindicated near term; bismuth subsalicylate is contraindicated due to risk of premature closure of ductus arteriosus and other salicylate effects. Overall: Contraindicated in all trimesters due to known risks of tetracycline (fetal bone and teeth), metronidazole (potential teratogenicity), and bismuth subsalicylate (salicylate effects). |
| Fetal Monitoring | If inadvertent exposure occurs, fetal monitoring should include ultrasound for skeletal abnormalities and tooth development assessment. Maternal monitoring for liver function, renal function, and electrolyte abnormalities due to bismuth and metronidazole. Complete blood count for metronidazole-related neutropenia. Prothrombin time/INR if high-dose salicylate exposure. |
| Fertility Effects | Metronidazole may cause reversible oligospermia in males; tetracycline can affect spermatogenesis at high doses; bismuth subsalicylate has no known significant fertility effects. Overall, transient impairment of male fertility possible. Female fertility not significantly affected. |
| Avoid alcohol and alcohol-containing products during metronidazole therapy and for 48 hours after completion. Tetracycline absorption is reduced by dairy products (milk, cheese, yogurt), calcium-fortified foods, antacids, and iron supplements; separate administration by at least 2 hours. Bismuth may cause dark stools but no specific food restriction. |
| Clinical Pearls | This three-drug regimen is a first-line treatment for Helicobacter pylori infection. Bismuth subsalicylate confers anti-inflammatory and antimicrobial effects, metronidazole provides anaerobic coverage, and tetracycline inhibits bacterial protein synthesis. Compliance is critical; bismuth may cause black stools and tongue, which is benign but must be distinguished from GI bleeding. Tetracycline should not be taken with dairy, antacids, or iron supplements due to chelation. Avoid alcohol during metronidazole therapy and for 48 hours after to prevent disulfiram-like reaction. |
| Patient Advice | Take all medications exactly as prescribed for the full course, even if symptoms improve. · Bismuth may cause temporary blackening of the tongue and stools; this is harmless. · Avoid alcohol during treatment and for at least 48 hours after completing metronidazole to prevent severe nausea, vomiting, and flushing. · Do not take tetracycline with milk, yogurt, cheese, antacids, or iron supplements; space by at least 2 hours. · Use sun protection; tetracycline can increase photosensitivity. · If severe diarrhea, rash, or signs of C. difficile infection occur, contact your healthcare provider. |