💊 Equisul-SDT Vet Guide 2025 by Dr Duncan Houston

Welcome to this professional equine antibiotic guide authored by Dr Duncan Houston BVSc. This comprehensive 2025 overview focuses on Equisul-SDT—a combination oral liquid antibiotic for horses. We’ll explore its usage, dosage, clinical applications, safety, monitoring protocols, and veterinarian-led recommendations to ensure your horse receives the most effective care. 🐴✨

🔍 What Is Equisul-SDT?

Equisul-SDT is an FDA-approved, veterinary-prescribed oral liquid combining two key antimicrobial agents:

• Sulfadiazine: 333 mg/mL
• Trimethoprim: 67 mg/mL

These components work synergistically to inhibit bacterial folate metabolism, rendering the product **bactericidal** against susceptible pathogens. It is flavored (apple) for palatability and labeled specifically for equine use. 🧪

💨 Indications for Use

• Equisul-SDT is indicated for **lower respiratory infections** in horses caused by Streptococcus equi subsp. zooepidemicus.
• Effective against other common respiratory pathogens in clinical scenarios, though off-label use requires veterinary discretion.

💊 Dosing Guidelines

• Dose: 24 mg/kg body weight per day, split into two doses.
• Frequency: Every 12 hours for 10 days.
• Example: 500 kg horse receives 2.7 mL/100 lb = 13.5 mL twice daily.
• Shake well before each dose. Administer using a dosing syringe directly onto the back of the tongue.

🧬 Pharmacology & Mechanism of Action

Equisul-SDT’s two components inhibit **two separate enzymes** in the folate synthesis pathway, which is critical for bacterial DNA replication:

• Trimethoprim blocks dihydrofolate reductase.
• Sulfadiazine blocks dihydropteroate synthase.

This **synergistic mechanism** makes Equisul-SDT effective in reaching plasma concentrations above MIC₉₀ values for common pathogens throughout dosing intervals. 🧠

📈 Effectiveness in Field Trials

Clinical studies demonstrate:

• ≈59–61% of horses show clinical improvement after full treatment course.
• Success defined by reduction in nasal discharge, fever resolution, and normalized respiratory auscultation.

📉 Safety & Side Effects

Equisul-SDT is generally well tolerated, but side effects include:

• Up to **38%**: transient loose stools or mild diarrhea.
• Less than **1%**: mild colic, transient anorexia, fever, or reluctance to swallow.
• Rare (<0.5%): elevation in liver enzymes, creatinine, or albumin—especially with prolonged high doses.

Stop treatment and contact your vet if signs worsen or persist. 💬

🚨 Contraindications & Warnings

• Do not use in horses allergic to sulfonamides.
• Not tested for foals <1 yr, pregnant or lactating mares—use caution.
• Not for use in horses intended for human consumption.

🩺 Monitoring Recommendations

• Veterinary check-ups recommended during treatment course.
• For long-term or repeat courses: monitor CBC, kidney (BUN/creatinine), and liver enzymes (ALT, GGT, ALP).
• Check for adverse GI signs or metabolic stress, especially in sensitive horses.

🧼 Storage & Handling

• Store between 59–86 °F (15–30 °C), upright, and tightly sealed.
• Do not freeze. Shake well before use.
• Wear gloves when handling—sulfonamides can trigger allergic reactions in humans.

🧾 Summary Table

✅ Practical Vet Advice

Equisul-SDT is a safe and effective first-line option for lower respiratory tract infections in horses. Always follow your vet’s instructions exactly, and complete the full treatment course to avoid resistance. Ensure good hydration, monitor appetite and manure, and don’t hesitate to call your vet if symptoms don’t improve in 48–72 hours. 🐎💬

📲 Need Help?

If you have questions about Equisul-SDT dosing, monitoring, or alternatives, our team at Ask A Vet is ready to help. Download the Ask A Vet app for 24/7 veterinary guidance, medication trackers, and safe usage support from your phone. 🩺