Olsalazine Sodium
Sodium 3,3'-azobis(6-hydroxybenzoate)
Also known as: Dipentum · Rasal · azodisal sodium · dimesalamine · CI mordant yellow 5 · CI No. 14130 · CJ-91B · olsalazinum natricum · sodium azodisalicylate
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| For dogs who cannot tolerate sulfasalazine | 10-20 mg/kg | PO | three times daily | — | 🌎 NA |
| Chronic colitis | 10-20 mg/kg | PO | q8h | — | 🌎 NA |
| Chronic colitis | 10-15 mg/kg | PO | q8-12h | — | 🌎 NA |
| Chronic colitis | 5-10 mg/kg | PO | three times daily | — | 🌎 NA |
- Chronic colitis: Has had limited use in dogs without causing apparent side effects.
- Chronic colitis: Initially, then reduce gradually.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Olsalazine sodium is a locally acting gastrointestinal anti-inflammatory agent primarily used in veterinary medicine to treat chronic colitis in dogs.
It serves as an alternative for patients that are unresponsive to or cannot tolerate sulfasalazine (often due to the sulfa moiety causing side effects like keratoconjunctivitis sicca). Structurally, it is a prodrug consisting of two molecules of 5-aminosalicylic acid (5-ASA, mesalamine) linked by an azo bond. Because it lacks the sulfapyridine moiety found in sulfasalazine, it generally has a lower risk of inducing immune-mediated side effects, though tear production issues can still occasionally occur.
Clinical Pearl: While olsalazine is more expensive than sulfasalazine, its targeted delivery and lack of a sulfa component make it a valuable second-line therapy for inflammatory bowel disease (IBD) localized to the large intestine.
Mechanism of action
Olsalazine is a prodrug that passes through the stomach and small intestine largely intact.
Upon reaching the colon, bacterial azoreductase enzymes (produced by normal colonic flora) cleave the azo bond, releasing two molecules of 5-ASA (mesalamine).
- 5-ASA acts locally on the colonic mucosa.
- It inhibits the cyclooxygenase (COX) and lipoxygenase (LOX) pathways → decreasing the production of pro-inflammatory prostaglandins and leukotrienes.
- It also acts as a free radical scavenger, reducing oxidative tissue damage in the inflamed colon.
Safety & warnings
Contraindications
- Hypersensitivity to olsalazine or salicylates
Adverse effects
- Keratoconjunctivitis sicca (KCS / dry eye) - less frequent than with sulfasalazine
- Diarrhea (paradoxical worsening reported in humans)
- Vomiting (especially with overdose)
- Decreased motor activity (with overdose)
- Elevated ALT or AST
Precautions
Important Note: While the risk of Keratoconjunctivitis Sicca (KCS) is lower than with sulfasalazine, baseline and periodic Schirmer Tear Tests (STT) are still highly recommended.
- Renal Disease: Use with caution in animals with pre-existing renal disease, as rare nephrotoxicity has been reported in human patients.
- Pregnancy (FDA Category C): High-dose rat studies showed some fetal abnormalities. Use during pregnancy only when benefits outweigh the risks.
- Lactation: Oral olsalazine given to lactating rats produced growth retardation in pups. Use with caution in nursing patients.
- Hepatic: May cause increases in ALT or AST; monitor liver enzymes if used long-term.
Drug interactions
Olsalazine may increase prothrombin times in patients receiving warfarin.
Monitoring
- Clinical efficacy (resolution of colitis signs)
- Adverse effects (especially signs of KCS/dry eye)
- Schirmer Tear Test (STT) periodically
- Serum ALT and AST
Pharmacokinetics
Half-life
Absorption
Poorly absorbed systemically; approximately 98% of an oral dose reaches the colon intact.
Distribution
Acts locally within the lumen and mucosa of the colon.
Metabolism
Cleaved in the large intestine by bacterial azoreductases into 5-aminosalicylic acid (5-ASA, mesalamine).
Elimination
The small amount of drug that is absorbed systemically is rapidly eliminated.
Overdose
Overdosage in dogs may cause vomiting, diarrhea, and decreased motor activity.
- Toxicity: Dosages up to 2 grams/kg were not lethal in dogs.
- Treatment: Treat symptomatically and supportively. GI decontamination may be considered if a massive overdose was recently ingested.
Available products
Formulations
- Oral capsules
Human-labeled
- Olsalazine Sodium Oral Capsules: 250 mg; Dipentum® (UCB Pharma); (Rx)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store capsules at room temperature. Olsalazine sodium is stable under physiologic acidic and alkaline conditions.
Client information
- Administration: Give this medication with food to minimize stomach upset. Try to space the doses evenly throughout the day.
- Monitor for Dry Eye: Watch for thick, yellow/green eye discharge, squinting, or redness. This drug can occasionally decrease tear production (a condition called "dry eye" or KCS).
- Monitor Stool: Contact your veterinarian if your dog's diarrhea worsens after starting this medication.
Do not stop abruptly unless directed by your veterinarian, but seek advice if adverse effects occur.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.