Sulfasalazine

Sulfasalazine is an oral azo-linked prodrug that delivers the anti-inflammatory compound mesalamine to the colon. Its principal veterinary application is inflammatory large-bowel disease, particularly in dogs. Colonic bacterial metabolism is central to its delivery mechanism, making it pharmacologically different from systemic glucocorticoids or conventional antibacterial treatment.

Group

Colonic anti-inflammatory prodrug

Mechanism of Action

Colonic bacteria cleave sulfasalazine’s azo bond and release mesalamine, or 5-aminosalicylic acid, and sulfapyridine. Mesalamine acts locally on the colonic mucosa through several proposed mechanisms, including modulation of prostaglandin, leukotriene and inflammatory-cell signaling. This localized activity reduces inflammation in responsive colonic disease. The precise contribution of each pathway remains incompletely defined.

Dose Rates

Dogs

Use / stage	Dose	Route	Schedule	Instructions
Colitis	10–30 mg/kg	PO	Every 8–12 h
Inflammatory large-bowel disease	20–48.4 mg/kg	PO	Every 8 h	Maximum 1000 mg/dose; Maintain initial control for at least 4 weeks, then taper by response.
Inflammatory large-bowel disease low starting alternative	12.5 mg/kg	PO	Every 8 h
Chronic colitis	20–50 mg/kg	PO	Every 8 h	Maximum 1000 mg/dose; Often start 20-30 mg/kg and taper over weeks.
Chronic colitis	10–25 mg/kg	PO	Every 8 h	Up to 42 days; Reported initial 4-6 weeks, then taper.
Vasculitis adjunct	20–40 mg/kg	PO	Every 8 h
Vasculitis adjunct	25 mg/kg	PO	Every 8 h

Cats

Use / stage	Dose	Route	Schedule	Instructions
Colitis	20 mg/kg	PO	Every 12 h
Inflammatory large-bowel disease	10–20 mg/kg	PO	Every 24 h
Inflammatory large-bowel disease short course	10–20 mg/kg	PO	Every 8–12 h	Up to 10 days

Ferrets

Use / stage	Dose	Route	Schedule	Instructions
Inflammatory bowel disease	10–20 mg/kg	PO	Every 8–12 h
Inflammatory bowel disease	25 mg/animal	PO	Every 12 h

Indications

Treatment of selected chronic inflammatory colitis or idiopathic large-bowel disease in dogs.
Specialist treatment of selected inflammatory colonic disease in cats, with a smaller clinical evidence base.
Historical adjunctive treatment of selected canine vasculitis, with limited evidence of efficacy.

Contraindications

Sulfonamide hypersensitivity

Interactions

Potential sulfonamide interactions include warfarin and antifolate drugs; mesalamine can increase azathioprine toxicity by interfering with thiopurine metabolism.

Adverse effects

Dry eye, hypersensitivity, skin reactions and thyroid suppression.

Toxicity

Large exposure can cause sulfonamide and salicylate toxicity. Assess hydration, renal function, acid-base status and CBC; selected severe cases require enhanced elimination.

Preparations

Preparation	Form	Strength	Route
Sulfasalazine 500 mg	Tablet	500 mg / tablet	PO

Monitoring and Administration

Monitor tear production during chronic canine treatment and combine with dietary management when appropriate. Compounded stability is unestablished.

Response-linked canine taper alternatives reduce the daily frequency, then amount over 2-4-week intervals, or decrease 25% every 2 weeks after remission. One report gives 20-40 mg/kg every 8 hours for 3 weeks, then every 12 hours for 3 weeks, then 10-20 mg/kg every 12 hours for 3 weeks but omits the route. Do not assume all taper schedules are equivalent.