BISMUTH SUBCITRATE POTASSIUM, METRONIDAZOLE AND TETRACYCLINE HYDROCHLORIDE
Clinical safety rating: avoid
Antacids and calcium supplements decrease absorption Can cause photosensitivity and tooth discoloration in children.
Bismuth subcitrate potassium forms a protective coating on gastric mucosa, binds to bile acids, and has antibacterial activity against Helicobacter pylori. Metronidazole inhibits nucleic acid synthesis by disrupting bacterial DNA, while tetracycline hydrochloride inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit.
| Metabolism | Metronidazole is metabolized primarily by hepatic oxidation via CYP450 enzymes (CYP2A6, CYP2B6, CYP2C9, CYP2D6, CYP3A4) to active metabolites. Tetracycline is not extensively metabolized and is excreted unchanged in urine and feces. Bismuth is not metabolized. |
| Excretion | Metronidazole: 60-80% renal (as unchanged drug and metabolites), 6-15% fecal; Tetracycline: 60% renal (glomerular filtration), 40% fecal (biliary and unabsorbed); Bismuth subcitrate: >99% fecal as insoluble bismuth sulfide. |
| Half-life | Metronidazole: 8 hours (range 6-10), prolonged in hepatic impairment; Tetracycline: 6-11 hours (normal renal function), 57-120 hours in anuria; Bismuth subcitrate: negligible systemic absorption, elimination follows transit (~24-72 hours). |
| Protein binding | Metronidazole: <20% bound; Tetracycline: 20-65% bound (decreasing with higher concentrations); Bismuth subcitrate: negligible binding. |
| Volume of Distribution | Metronidazole: 0.6-0.8 L/kg; Tetracycline: 1.3-1.7 L/kg; Bismuth subcitrate: not applicable (locally acting, minimal absorption). |
| Bioavailability | Metronidazole: >90% oral; Tetracycline: 75-80% oral (decreased by food/dairy); Bismuth subcitrate: <0.5% oral (as bismuth, mostly not absorbed). |
| Onset of Action | Metronidazole and tetracycline: therapeutic effect begins within 2-3 days of oral dosing; bismuth: local effect on H. pylori within hours of administration. |
| Duration of Action | Metronidazole and tetracycline: duration of bactericidal effect mirrors half-life (~12-24 hours); bismuth: local mucosal protection persists for 1-2 hours after dose. Clinical regimen duration: 7-14 days. |
| Molecular Weight | 148.34 |
For Helicobacter pylori eradication: 1 tablet (bismuth subcitrate potassium 140 mg, metronidazole 125 mg, tetracycline hydrochloride 125 mg) orally 4 times daily (with meals and at bedtime) for 14 days, plus a proton pump inhibitor.
| Dosage form | CAPSULE |
| Renal impairment | Contraindicated if CrCl <30 mL/min. For CrCl 30-60 mL/min: reduce metronidazole dose by 50% (use alternative components individually). Tetracycline and bismuth may accumulate; avoid combination product. |
| Liver impairment | Child-Pugh A: no adjustment. Child-Pugh B: reduce metronidazole dose by 50%. Child-Pugh C: contraindicated (metronidazole and tetracycline may precipitate hepatic encephalopathy). |
| Pediatric use | Safety and efficacy not established in children <12 years. For children ≥12 years: same as adult dosing (1 tablet orally 4 times daily for 14 days). |
| Geriatric use | Use with caution; consider renal function (CrCl may be reduced). No specific dose adjustment based solely on age, but monitor for tetracycline and metronidazole toxicity. Avoid if CrCl <30 mL/min. |
| 1st trimester | Contraindicated due to risk of tetracycline causing fetal bone and tooth development issues and metronidazole's potential carcinogenicity based on animal studies. |
| 2nd trimester | Contraindicated due to tetracycline's effects on fetal skeletal development and dental discoloration; metronidazole is generally avoided unless necessary. |
| 3rd trimester | Contraindicated due to tetracycline causing permanent tooth discoloration and inhibition of bone growth; metronidazole use in late pregnancy is associated with potential neonatal effects. |
Clinical note
Antacids and calcium supplements decrease absorption Can cause photosensitivity and tooth discoloration in children.
| FDA category | Positive |
| Placental transfer | Tetracycline and metronidazole cross the placenta; tetracycline binds to fetal tissues, and metronidazole achieves fetal concentrations similar to maternal. |
■ FDA Black Box Warning
Metronidazole is carcinogenic in animal studies; tetracycline may cause permanent discoloration of teeth during tooth development (last half of pregnancy, infancy, and childhood to age 8 years) and should not be used in these age groups unless other drugs are unlikely to be effective or are contraindicated.
| Common Effects | acne |
| Serious Effects |
Hypersensitivity to any componentPregnancyBreastfeedingChildren under 8 years (tetracycline)Severe hepatic impairment (metronidazole)Concurrent use of disulfiram or alcohol (metronidazole)
| Precautions | Tetracycline: May cause photosensitivity, avoid prolonged sun exposure., Metronidazole: Disulfiram-like reaction with alcohol; avoid alcohol during therapy and for 3 days after., Tetracycline: May increase intracranial pressure or impair bone growth in children., Metronidazole: Peripheral neuropathy (signs of numbness/tingling) may occur., Tetracycline: Use with caution in renal impairment; may accumulate., Bismuth: May cause darkening of tongue and stool., Pregnancy: Tetracycline contraindicated; metronidazole and bismuth are Category B. |
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| Breastfeeding | Tetracycline is excreted in breast milk and may cause dental staining and bone growth suppression in nursing infants. Metronidazole is also excreted and can cause a metallic taste, though the risk is low with single-dose therapy. Bismuth subsalicylate is contraindicated due to salicylate absorption. Avoid breastfeeding during therapy and for 3-5 days after last dose. |
| Lactation Rating | Avoid |
| Teratogenic Risk | First trimester: Metronidazole and tetracycline are associated with teratogenic effects. Tetracycline use is contraindicated after the first trimester due to risk of fetal skeletal and dental abnormalities. Metronidazole is generally avoided in first trimester but data are conflicting. Bismuth subcitrate potassium is minimally absorbed, likely low risk. Overall, combination is contraindicated in pregnancy. |
| Fetal Monitoring | Monitor for maternal gastrointestinal adverse effects, potential metronidazole neurotoxicity (peripheral neuropathy, CNS effects), and tetracycline hepatotoxicity. Fetal monitoring for growth and development if inadvertent exposure occurs. |
| Fertility Effects | No specific human data on fertility effects. Tetracycline may affect spermatogenesis in animal studies; metronidazole has minimal reported effects. Clinical significance unknown. |
| Food/Dietary | Avoid dairy products (milk, cheese, yogurt), antacids, iron supplements, and calcium-rich foods within 2-3 hours of tetracycline administration as they reduce absorption. Avoid alcohol during metronidazole therapy and for 48 hours after completion. Bismuth may be taken with or without food; however, to optimize adherence, take all four drugs together with a meal if tolerated, but separate tetracycline from dairy/antacids by at least 2 hours. |
| Clinical Pearls | This quadruple therapy regimen (bismuth subcitrate potassium, metronidazole, tetracycline) is a first-line option for Helicobacter pylori eradication, particularly in areas with high clarithromycin resistance. Avoid alcohol during metronidazole therapy and for 48 hours after completion due to disulfiram-like reaction. Tetracycline can cause esophageal ulceration; advise taking with a full glass of water and remaining upright for 30 minutes after dosing. Metronidazole may cause metallic taste, which is harmless but should be disclosed. Bismuth darkens stools and tongue; warn patients to avoid confusion with melena. Assess renal function before use; tetracycline is contraindicated in severe renal impairment. Avoid use in pregnancy (tetracycline category D; metronidazole category B but avoid in first trimester if possible). |
| Patient Advice | Take all medications exactly as prescribed for the full course (typically 10-14 days) even if symptoms improve. · Do not consume alcohol or alcohol-containing products during metronidazole treatment and for 48 hours after finishing; this can cause severe nausea, vomiting, and headache. · Take tetracycline on an empty stomach (1 hour before or 2 hours after meals) with a full glass of water; do not take with dairy products, antacids, or iron supplements. · Bismuth will turn your stools black and may darken your tongue; this is harmless and temporary. · Metronidazole may cause a metallic taste in your mouth; this is not harmful. · Avoid sun exposure or use sunscreen; tetracycline can increase sensitivity to sunlight. · Do not lie down for at least 30 minutes after taking tetracycline to prevent esophageal irritation. · Inform your doctor if you are pregnant, planning to become pregnant, or breastfeeding. |