Bismuth Subsalicylate — Veterinary Vademecum Drug Reference

Dosage & Administration Guidelines

Species	Route	Dose	Frequency	Duration & Clinical Notes
Dog	PO	10-30 mg/kg	q6-8h	Duration: 2-5 days or until diarrhea resolves Notes: Use the lower end for large dogs. Administer with food to reduce GI upset. Do not use for more than 3 days without veterinary consultation.
Cat	PO	5-10 mg/kg (use with extreme caution)	q12-24h	Duration: 1-2 days maximum Notes: Cats are sensitive to salicylates; use only if no alternative and under veterinary supervision. Monitor for signs of salicylate toxicity.
Horse	PO	Not recommended	N/A	Duration: N/A Notes: Not indicated; other safer antidiarrheals are available.
Cattle	PO	Not recommended	N/A	Duration: N/A Notes: Not indicated for food animals due to lack of efficacy data and withdrawal concerns.

Clinical Indications & Species Uses

General Indications

Symptomatic treatment of acute diarrhea
Gastric mucosal protection
Antacid effect

Dog (Canine)

Treatment of acute diarrhea
Symptomatic relief of gastritis
Reduction of intestinal inflammation
Adjunct in treatment of Helicobacter pylori infection

Cat (Feline)

Treatment of acute diarrhea (use with caution due to salicylate sensitivity)
Symptomatic relief of gastritis (limited use)

Pharmacology & Mechanism of Action

Drug Class: Antidiarrheal, Gastroprotective | Pharmacological Group: Bismuth compound, Salicylate

Mechanism of Action: Bismuth subsalicylate exerts its effects through multiple mechanisms. The bismuth component has mild antimicrobial activity against certain enteropathogens (e.g., Escherichia coli, Salmonella spp.) and forms a protective coating over the gastric and intestinal mucosa, reducing inflammation and fluid secretion. The salicylate moiety, after hydrolysis in the gastrointestinal tract, provides prostaglandin synthesis inhibition (via cyclooxygenase inhibition), reducing intestinal inflammation and fluid secretion. Additionally, it may bind bacterial toxins and reduce intestinal motility.

Pharmacodynamics: Bismuth subsalicylate reduces the frequency and fluidity of diarrheal stools, decreases intestinal inflammation, and provides mild antacid and cytoprotective effects. It also has antiemetic properties. The salicylate component is absorbed systemically and can produce anti-inflammatory and analgesic effects, but at typical doses, systemic effects are minimal.

⚡ Pharmacokinetics Summary

Absorption: Bismuth subsalicylate is minimally absorbed from the gastrointestinal tract. The bismuth component remains largely in the gut, while the salicylate moiety is absorbed after hydrolysis. In dogs, salicylate absorption is variable and may be enhanced by concurrent food intake.

Distribution: Bismuth is distributed primarily in the gastrointestinal tract and is not significantly absorbed systemically. Salicylate, once absorbed, is distributed throughout the body, but at typical doses, plasma concentrations are low.

Metabolism: Bismuth subsalicylate is hydrolyzed in the stomach to bismuth and salicylic acid. Salicylic acid is metabolized in the liver to salicyluric acid and other metabolites. Bismuth is not metabolized.

Excretion: Bismuth is excreted in the feces. Salicylate and its metabolites are excreted primarily in the urine, with some biliary excretion. The elimination half-life of salicylate in dogs is approximately 8-12 hours, but may be longer in cats.

Half-Life: Salicylate: Dogs ~8-12 hours; Cats ~20-30 hours (due to slower metabolism). Bismuth: Not systemically absorbed, so no meaningful half-life.

Bioavailability: Bismuth subsalicylate has low systemic bioavailability due to poor absorption of bismuth and variable absorption of salicylate. Oral bioavailability of salicylate is approximately 50-80% in dogs.

Protein Binding: Salicylate is approximately 50-80% bound to plasma proteins, primarily albumin. Bismuth is not protein-bound.

Available Formulations & Strengths

Oral Suspension 87 mg/mL (Pepto-Bismol), 262 mg/15 mL (generic) (PO)

Chewable Tablet 262 mg, 525 mg (PO)

Caplet 262 mg (PO)

Contraindications & Clinical Warnings

Contraindications:

Hypersensitivity to bismuth subsalicylate or salicylates
Concurrent use with other salicylates or NSAIDs (increased risk of salicylate toxicity)
Known bleeding disorders (e.g., thrombocytopenia, coagulopathy)
Gastrointestinal ulceration or obstruction
Cats with renal or hepatic impairment (relative contraindication)
Pregnancy (especially third trimester) due to salicylate effects
Neonates and young animals (increased risk of salicylate toxicity)

Warnings & Clinical Precautions:

Use with caution in cats due to slow salicylate metabolism and increased risk of toxicity.
May cause blackening of the tongue and feces (bismuth sulfide formation), which is harmless but may interfere with diagnostic tests.
Salicylate may be absorbed systemically; avoid prolonged use or high doses.
Use with caution in animals with renal or hepatic disease.
Do not use in animals with suspected GI obstruction or perforation.
In food animals, observe withdrawal times; not approved for use in food animals.
Avoid use in animals with known bleeding disorders or those on anticoagulant therapy.

Adverse Effects & Reactions

Common:

Blackening of the tongue and feces
Constipation
Nausea
Vomiting (rare)

Serious / Severe:

Salicylate toxicity (tinnitus, hyperthermia, metabolic acidosis, respiratory alkalosis, seizures)
GI ulceration or bleeding (with high doses or prolonged use)
Renal toxicity (with high doses)

Rare:

Hypersensitivity reactions
Bismuth encephalopathy (with chronic high-dose use)

Key Drug Interactions

Interacting Drug / Class	Clinical Effect & Mechanism	Severity
Aspirin or other salicylates	Additive salicylate toxicity	High
NSAIDs (e.g., carprofen, meloxicam)	Increased risk of GI ulceration and bleeding	High
Anticoagulants (e.g., warfarin, heparin)	Increased risk of bleeding due to platelet inhibition	High
Tetracycline antibiotics	Reduced absorption of tetracycline due to bismuth binding	Moderate
Fluoroquinolones (e.g., enrofloxacin)	Reduced absorption of fluoroquinolones due to bismuth binding	Moderate
Methotrexate	Increased methotrexate toxicity due to reduced renal clearance	Moderate
ACE inhibitors	Reduced antihypertensive effect	Mild

Overdose & Toxicity Management

Signs of Toxicity:

Salicylate toxicity: hyperthermia, tachypnea, respiratory alkalosis, metabolic acidosis, vomiting, diarrhea, depression, seizures, coma
GI irritation and bleeding
Renal failure (with chronic overdose)

Emergency Treatment Protocol: Induce vomiting if recent ingestion and animal is stable. Administer activated charcoal to reduce absorption. Provide supportive care: IV fluids, correction of acid-base and electrolyte imbalances, cooling for hyperthermia. In severe cases, consider alkalinization of urine to enhance salicylate excretion. Monitor renal and hepatic function. There is no specific antidote for bismuth toxicity.

Food Animal Withdrawal Times

Not approved for use in food animals. If used off-label, a withdrawal period of at least 30 days for meat and 7 days for milk is recommended, but consult regulatory guidelines.

Storage, Handling & Regulatory Information

Storage Temperature: Store at room temperature (15-30°C)

Handling & Special Conditions: Keep container tightly closed. Do not freeze. Protect from excessive heat.

Dispensing Status: Over-The-Counter (OTC)

Approval Status: Not FDA-approved for veterinary use; available as an OTC human product.

Extra-Label (Off-Label) Use: In the US, bismuth subsalicylate is an OTC human drug that may be used in animals under the Animal Medicinal Drug Use Clarification Act (AMDUCA) for extra-label use, but it is not FDA-approved for veterinary use. Extra-label use in food animals is prohibited if it results in violative residues.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Bismuth subsalicylate is a useful adjunct for symptomatic treatment of acute diarrhea in dogs, but it is not a primary therapy and should be used with supportive care (fluid/electrolyte replacement). It is generally safe in dogs at appropriate doses, but caution is advised in cats due to their slow salicylate metabolism. It should not be used in animals with known bleeding disorders or those on anticoagulants. The blackening of feces is a harmless side effect but may be mistaken for melena. For chronic or severe diarrhea, investigate underlying causes. In food animals, avoid use due to lack of approval and withdrawal concerns.

References & Literature

📚 Plumb's Veterinary Drug Handbook
📚 Papich Veterinary Pharmacology and Therapeutics
📚 Compendium of Veterinary Products (CVP)