What is phthalylsulfathiazole used for in veterinary medicine?

Primary veterinary uses include: (1) bacterial enteritis and colibacillosis in calves, piglets, and poultry; (2) adjuvant therapy with anticoccidials to control secondary bacterial overgrowth during Eimeria infections; (3) preoperative bowel preparation before gastrointestinal surgery to reduce intestinal bacterial load; and (4) intestinal antisepsis for nonspecific diarrhea. It is most commonly administered orally as a powder mixed in feed or drinking water.

Why use phthalylsulfathiazole instead of other sulfonamides?

Three key advantages over systemic sulfonamides like sulfadiazine or sulfamethazine: (1) Minimal systemic absorption (<5%) means low tissue residues and short withdrawal periods, important for food-producing animals; (2) localized action in the gut lumen targets enteric infections directly without systemic exposure; (3) reduced risk of crystalluria and renal toxicity since the drug is not concentrated in the kidneys. It is the preferred sulfonamide when the infection is confined to the gastrointestinal tract.

What quality specifications should I check when sourcing phthalylsulfathiazole?

Key quality parameters include: assay (HPLC) of 98.0-102.0% on the dried basis per BP monograph; free sulfathiazole content (a degradation/process impurity) should be below 0.5%; loss on drying typically 0.5% maximum; residue on ignition 0.1% maximum; and heavy metals at 20 ppm or below. Request a batch-specific CoA, residual solvent statement per ICH Q3C, and GMP certificate. For food-producing animal use, confirm with your supplier that the product meets the relevant withdrawal period requirements in your market.

Phthalylsulfathiazole | CAS 85-73-4 | Veterinary API Supplier China

Name: Phthalylsulfathiazole
SKU: 85-73-4
Availability: InStock

Phthalylsulfathiazole pharmaceutical raw material

Quick Facts

CAS Number	85-73-4
Molecular Formula	C₁₇H₁₃N₃O₅S₂
Molecular Weight	403.44
Pharmacopoeia	BP
Packaging	25 KG/DRUM

GMP Certified BP Standard

Product Overview

Phthalylsulfathiazole emerged from a deliberate medicinal chemistry effort in the early 1940s to create sulfonamide antibiotics that remain confined to the gut lumen. Researchers at major pharmaceutical laboratories recognized that systemic sulfonamides like sulfathiazole carried risks of crystalluria and renal toxicity, while many enteric infections required only local antibacterial action. By adding a phthalyl group to the N4 position of sulfathiazole, they created a prodrug that passes through the stomach and small intestine intact, only releasing active sulfathiazole upon hydrolysis by colonic bacteria. The first clinical reports in The New England Journal of Medicine (1944) demonstrated its efficacy against enteric pathogens, and it has remained in veterinary use ever since.

The defining pharmacokinetic feature of phthalylsulfathiazole is its deliberately poor absorption profile. Approximately 95% of an oral dose remains within the gastrointestinal tract, achieving high luminal concentrations at the site of enteric infection while producing negligible serum levels. This is the opposite design goal of most oral pharmaceuticals, where high bioavailability is desirable. For gastrointestinal infections in livestock and poultry, this localized delivery provides effective antibacterial action without the systemic exposure, tissue residues, and milk/egg withdrawal concerns associated with absorbed sulfonamides.

Phthalylsulfathiazole is frequently used as an adjuvant to anticoccidial therapy. During clinical coccidiosis caused by Eimeria species, damage to the intestinal epithelium allows secondary bacterial invasion that compounds morbidity and mortality. Adding phthalylsulfathiazole to the treatment protocol suppresses bacterial overgrowth while the anticoccidial clears the protozoal infection, resulting in faster clinical recovery and reduced mortality compared to anticoccidial monotherapy. This combination approach has been standard practice in poultry production in Asia, Africa, and Latin America since the 1970s.

As of mid-2026, phthalylsulfathiazole occupies a specialized but stable niche in the veterinary API market. While overall sulfonamide volumes have declined in favor of newer antibiotic classes, the gut-targeted prodrugs (phthalylsulfathiazole and succinylsulfathiazole) retain strong demand in poultry and swine operations where low tissue residues and short withdrawal periods are essential. China is the dominant global producer, with manufacturing concentrated in Shandong and Jiangsu provinces. KingWish supplies GMP-certified phthalylsulfathiazole meeting BP specifications, supporting veterinary pharmaceutical manufacturers in emerging livestock markets worldwide.

Quality Specifications

Purity (HPLC)	≥ 98.0% (dried basis), per BP monograph
Free Sulfathiazole	≤ 0.5% (key degradation/process impurity per BP)
Related Substances	Individual impurity ≤ 0.5%, total impurities ≤ 1.0%
Residual Solvents	Compliant with ICH Q3C
Heavy Metals	≤ 20 ppm
GMP Status	Manufactured under ICH Q7 GMP conditions

Veterinary Applications

Bacterial Enteritis (Poultry & Swine)

Oral powder at 0.1-0.3 g/kg body weight for E. coli enteritis and colibacillosis. Includes salmonellosis and other enteric bacterial infections with minimal systemic exposure.

Coccidiosis Adjuvant Therapy

Adjunct to anticoccidials (toltrazuril, amprolium) for reducing secondary bacterial overgrowth during Eimeria infections. Improves clinical recovery and reduces mortality in broilers and layers.

Therapeutic Areas

Poultry: Enteric bacterial infections, colibacillosis, coccidiosis adjuvant therapy
Swine: Piglet scours, bacterial enteritis, pre-weaning diarrhea
Cattle & Calves: Calf scours, preoperative bowel antisepsis
Small Ruminants: Enteric infections, intestinal antisepsis

Sourcing Phthalylsulfathiazole: Key Checks

Documentation

Request CoA with HPLC purity data and free sulfathiazole content (BP requires this impurity test), residual solvent statement (ICH Q3C), heavy metals report, and GMP certificate. The BP monograph is the primary pharmacopoeia reference for this product.

Red Flags

Elevated free sulfathiazole above 0.5% (indicates degradation during storage or incomplete synthesis), missing specific BP impurity tests, reluctance to share batch CoA, and inconsistent powder color or odor between batches.

Packaging & Logistics

Standard: 25 KG/DRUM with PE liner. Store in a cool, dry place protected from light. Standard lead time 4-6 weeks. Sea freight is the most economical shipping method for bulk orders; air freight available for smaller quantities.

Market Context

Phthalylsulfathiazole is a niche but stable product in the global veterinary API market. It competes with newer gut-targeted antibiotics but retains strong demand in poultry and swine operations in Asia, Africa, and Latin America where cost-effectiveness and minimal withdrawal periods are prioritized. China dominates global production.

Frequently Asked Questions

Phthalylsulfathiazole is a prodrug designed for minimal absorption from the stomach and small intestine. When it reaches the large intestine, bacterial enzymes hydrolyze the phthalyl group, releasing active sulfathiazole locally at the site of enteric infection. This targeted delivery achieves high luminal concentrations while keeping systemic absorption below 5%. The result is effective local antibacterial action against enteric pathogens with minimal systemic side effects, low tissue residues, and short withdrawal periods for food-producing animals.

Primary veterinary uses include: (1) bacterial enteritis and colibacillosis in calves, piglets, and poultry — typically 0.1-0.3 g/kg body weight orally; (2) adjuvant therapy with anticoccidials (toltrazuril, amprolium) to control secondary bacterial overgrowth during Eimeria infections — this combination improves recovery rates compared to anticoccidial monotherapy; (3) preoperative bowel preparation before gastrointestinal surgery to reduce intestinal bacterial load; and (4) intestinal antisepsis for nonspecific diarrhea in livestock.

Three key advantages over systemic sulfonamides (sulfadiazine, sulfamethazine, sulfadimidine): (1) Minimal systemic absorption — less than 5% of an oral dose reaches the bloodstream, meaning low tissue residues and short withdrawal periods essential for food-producing animals; (2) localized luminal action — the drug concentrates where enteric infections occur rather than distributing throughout the body; (3) reduced crystalluria risk — since the drug is not concentrated in the kidneys, the risk of sulfonamide crystal precipitation in renal tubules is eliminated. It is the preferred sulfonamide when the infection is confined to the gastrointestinal tract.

Key quality parameters per the BP monograph: assay (HPLC) of 98.0-102.0% on the dried basis; free sulfathiazole content (a degradation and process impurity) should be 0.5% or below — values above this indicate either incomplete synthesis or degradation during storage; loss on drying 0.5% maximum; residue on ignition 0.1% maximum; and heavy metals at 20 ppm or below. Always request a batch-specific CoA, residual solvent statement per ICH Q3C, and GMP certificate (ICH Q7). For food-producing animal formulations, confirm the product meets the relevant MRL and withdrawal requirements in your target market.

Standards: BP | CAS: 85-73-4 | Quality data verified against pharmacopoeia monograph COA and MSDS available | DrugBank | July 2026