Complete Sulfadimethoxine Dosage Guide

Key Takeaways

Introduction

Sulfadimethoxine is a long-acting sulfonamide antibiotic used extensively in veterinary medicine for treating bacterial and protozoal infections. As a broad-spectrum antimicrobial agent, it works by inhibiting folic acid synthesis in susceptible organisms, making it particularly effective against:

This comprehensive guide provides evidence-based dosing information for veterinary professionals and informed pet owners across all common species.

Understanding Sulfadimethoxine Pharmacology

Mechanism of Action

Sulfadimethoxine is a bacteriostatic agent that inhibits the enzyme dihydropteroate synthetase, blocking bacterial folic acid synthesis. This prevents bacterial DNA replication and protein synthesis, ultimately limiting bacterial growth.

Pharmacokinetics

Clinical Significance

The long half-life of sulfadimethoxine allows for convenient once-daily dosing, improving client compliance compared to shorter-acting sulfonamides.

Dosage by Species

Dogs (Canine Dosing)

Standard Protocol:
- Loading Dose (Day 1): 55 mg/kg PO once
- Maintenance Dose (Days 2-7): 27.5 mg/kg PO once daily

Alternative Protocol (Some references):
- Unified Dose: 50 mg/kg PO once daily for 5-7 days

Clinical Considerations:
- Larger dogs (>40 kg): May require dose adjustment
- Puppies ( months): Use with caution, monitor hydration closely
- Geriatric dogs: Monitor renal function before and during treatment
- Concurrent medications: Check for drug interactions

Common Indications in Dogs:
- Coccidiosis (Isospora canis)
- Respiratory infections (as part of combination therapy)
- Soft tissue infections

Cats (Feline Dosing)

Standard Protocol:
- Loading Dose (Day 1): 50 mg/kg PO once
- Maintenance Dose (Days 2-5): 25 mg/kg PO once daily

Clinical Considerations:
- Cats are more sensitive to sulfonamides than dogs
- Shorter treatment duration recommended (5 days maximum typically)
- Monitor for signs of adverse reactions (lethargy, anorexia, vomiting)
- Ensure adequate hydration throughout treatment
- Avoid in cats with pre-existing renal disease

Common Indications in Cats:
- Coccidiosis (Isospora felis, I. rivolta)
- Toxoplasmosis (combination therapy with pyrimethamine)
- Upper respiratory infections (as adjunct therapy)

Important: Cats metabolize sulfonamides differently than dogs. Close monitoring is essential.

Cattle (Bovine Dosing)

Standard Protocol:
- Loading Dose (Day 1): 55 mg/kg PO or IV once
- Maintenance Dose (Days 2-5): 27.5 mg/kg PO or IV once daily

Injectable Formulation (40% solution):
- 137.5 mg/kg IV or IM on Day 1
- 68.75 mg/kg IV or IM daily thereafter

Clinical Considerations:
- Withdrawal Times:
- Meat: 7-10 days (varies by formulation - check label)
- Milk: NOT approved for lactating dairy cattle in most jurisdictions
- Large volume injections may require multiple injection sites
- Monitor injection sites for reactions
- Ensure adequate water intake

Common Indications in Cattle:
- Bovine respiratory disease complex (BRDC)
- Coccidiosis in calves (Eimeria species)
- Foot rot (as adjunct to topical therapy)
- Metritis and other soft tissue infections

Poultry (Avian Dosing)

Water Medication:
- Standard Concentration: 0.05-0.1% solution (500-1000 mg per liter)
- Duration: 3-5 days
- Preparation: Dissolve powder in drinking water, replace daily

Feed Medication:
- Concentration: 0.015-0.025% in feed
- Duration: 5-7 days

Individual Bird Dosing (Companion Birds):
- Dose: 25-50 mg/kg PO once daily
- Duration: 5-7 days

Clinical Considerations:
- Ensure all birds have access to medicated water
- Fresh water solution daily (degrades in sunlight)
- Monitor water consumption (sick birds may not drink adequately)
- Egg Withdrawal: 3-5 days (varies by jurisdiction - check regulations)

Common Indications in Poultry:
- Coccidiosis (Eimeria tenella, E. necatrix, E. acervulina, others)
- Fowl cholera (combination therapy)
- Respiratory infections (as adjunct)

Swine (Porcine Dosing)

Standard Protocol:
- Loading Dose: 55 mg/kg PO once
- Maintenance Dose: 27.5 mg/kg PO once daily for 3-5 days

Water Medication (Therapeutic levels):
- 0.02-0.04% in drinking water

Clinical Considerations:
- Withdrawal Time: 15 days (verify label for specific product)
- Use in breeding stock: Generally safe, but consult regulations
- Monitor for reduced feed/water intake
- Adequate hydration essential

Common Indications in Swine:
- Swine dysentery
- Atrophic rhinitis (adjunct therapy)
- Pneumonia (combination therapy)

Sheep and Goats (Small Ruminants)

Standard Protocol:
- Dose: 50 mg/kg PO once daily
- Duration: 3-5 days

Clinical Considerations:
- Withdrawal Times (Extra-label use):
- Meat: Minimum 10 days (consult veterinarian)
- Milk: NOT recommended in lactating animals producing milk for human consumption
- Small ruminants may require extra-label use (not FDA-approved in all countries)
- Monitor for signs of toxicity

Common Indications:
- Coccidiosis in lambs/kids (Eimeria species)
- Pneumonia (adjunct therapy)
- Foot rot

Horses (Equine Dosing)

Standard Protocol (Extra-label use):
- Dose: 15-20 mg/kg PO once daily
- Duration: 3-5 days

Clinical Considerations:
- Extra-label use: Not FDA-approved for horses in many jurisdictions
- Use only under veterinary supervision
- Monitor for signs of adverse reactions (rare but can include hypersensitivity)
- Ensure adequate hydration

Potential Indications (consult veterinarian):
- Protozoal infections
- Respiratory infections (adjunct)

Note: Sulfadiazine-trimethoprim combination is more commonly used in horses for many indications.

Rabbits and Small Mammals

Rabbits:
- Dose: 50 mg/kg PO once daily
- Duration: 5-10 days (longer for coccidiosis)
- Primary indication: Coccidiosis (Eimeria species)

Guinea Pigs, Chinchillas:
- Dose: 25-50 mg/kg PO once daily
- Duration: 5-7 days
- Caution: Monitor closely for GI upset

Ferrets:
- Dose: 50 mg/kg PO once daily
- Duration: 5-7 days

Clinical Considerations for Small Mammals:
- Many small mammals have sensitive GI flora
- Monitor for diarrhea, anorexia, or lethargy
- Ensure adequate hydration and nutrition
- Probiotic supplementation may be beneficial

Formulation and Administration

Available Formulations

  1. Oral Tablets:

    • Common strengths: 125 mg, 250 mg, 500 mg
    • Can be divided for accurate dosing in small animals
    • Administer with food to reduce GI upset

  2. Oral Suspension:

    • Common concentration: 50 mg/mL (5%)
    • Shake well before use
    • Refrigerate after opening (check label)
    • Accurate measurement essential (use calibrated syringe)

  3. Oral Powder:

    • For mixing in feed or water
    • Weigh accurately for proper concentration
    • Mix thoroughly to ensure even distribution

  4. Injectable Solution:

    • Typical concentration: 40% (400 mg/mL)
    • IV or IM administration
    • Large volumes may require multiple injection sites

Administration Tips

Oral Administration:
- Administer with small amount of food (unless fasted required)
- Ensure complete dose swallowed
- Follow with water to aid swallowing and reduce esophageal irritation

Injectable Administration:
- Use aseptic technique
- Rotate injection sites for multiple-day treatment
- IM injections: Deep into muscle mass, avoid major nerves/vessels
- IV injections: Slow administration to minimize adverse reactions

Dosage Calculations

Example Calculations

Example 1: Dog (20 kg)

Loading Dose: 55 mg/kg × 20 kg = 1,100 mg

Using 250 mg tablets: 1,100 mg ÷ 250 mg = 4.4 tablets → Round to 4.5 tablets (1,125 mg)

Maintenance Dose: 27.5 mg/kg × 20 kg = 550 mg
Using 250 mg tablets: 550 mg ÷ 250 mg = 2.2 tablets (split one tablet)

Example 2: Cat (4 kg)

Loading Dose: 50 mg/kg × 4 kg = 200 mg

Using 50 mg/mL suspension: 200 mg ÷ 50 mg/mL = 4 mL

Maintenance Dose: 25 mg/kg × 4 kg = 100 mg
Using 50 mg/mL suspension: 100 mg ÷ 50 mg/mL = 2 mL

Example 3: Calf (100 kg)

Loading Dose: 55 mg/kg × 100 kg = 5,500 mg = 5.5 grams

Using 40% injectable (400 mg/mL): 5,500 mg ÷ 400 mg/mL = 13.75 mL

Treatment Duration by Indication

Coccidiosis

Bacterial Infections

Important Principles

Safety and Adverse Reactions

Common Side Effects (Usually Mild)

Serious Adverse Reactions (Rare)

Minimizing Risk

  1. Ensure Adequate Hydration: Encourage water intake throughout treatment
  2. Monitor Urine Output: Reduced urination may indicate crystalluria risk
  3. Avoid in Renal Disease: Contraindicated in pre-existing kidney dysfunction
  4. Monitor Long-term Use: CBC and chemistry panel if treatment exceeds 10 days
  5. Watch for Warning Signs: Discontinue and contact veterinarian if severe reactions occur

Contraindications

Absolute Contraindications

Relative Contraindications (Use with Caution)

Pregnancy and Lactation

Drug Interactions

Significant Interactions

  1. Warfarin and Anticoagulants:

    • Sulfadimethoxine displaces from protein binding
    • Effect: Enhanced anticoagulation (bleeding risk)
    • Management: Monitor clotting times, adjust dose

  2. Methotrexate:

    • Both drugs inhibit folic acid metabolism
    • Effect: Increased methotrexate toxicity
    • Management: Avoid combination if possible

  3. Phenytoin and Phenobarbital:

    • Sulfonamides may displace from protein binding
    • Effect: Increased risk of toxicity
    • Management: Monitor for signs of toxicity, adjust doses

  4. Thiazide Diuretics:

    • Increased risk of thrombocytopenia
    • Management: Monitor platelet count

  5. Local Anesthetics (Procaine, Benzocaine):

    • PABA-containing compounds may antagonize sulfonamide activity
    • Management: Avoid concurrent use

Moderate Interactions

Monitoring Parameters

Baseline Assessment (Before Starting Therapy)

During Therapy

Storage and Handling

Tablets and Powder

Oral Suspension

Injectable Solution

Regulatory Considerations

Food Animal Use

Extra-Label Drug Use (ELDU)

When using sulfadimethoxine in species or for indications not on the label:

  1. Valid Veterinary-Client-Patient Relationship (VCPR) required
  2. No approved drug available for intended use
  3. Extended withdrawal times for food animals (veterinarian determines)
  4. Proper labeling: Veterinarian must provide clear instructions
  5. Record keeping: Document rationale for ELDU

Frequently Asked Questions

Can sulfadimethoxine be used in pregnant animals?

Generally avoided, especially in the last trimester due to potential teratogenic effects. Use only if the benefits clearly outweigh the risks and under close veterinary supervision. Alternative antibiotics should be considered first.

What should I do if a dose is missed?

Administer the missed dose as soon as remembered, unless it’s close to the time for the next dose. Do not double dose. Maintain the regular dosing schedule. Contact your veterinarian if multiple doses are missed.

Can sulfadimethoxine be used with other antibiotics?

Yes, in many cases. Sulfadimethoxine is sometimes used in combination with other antimicrobials (e.g., trimethoprim). However, always consult a veterinarian before combining medications to avoid interactions or antagonism.

How long does it take to see improvement?

Typically 24-48 hours for most infections. If no improvement is seen within 72 hours, re-evaluation by a veterinarian is necessary. The infection may be caused by resistant organisms or require a different treatment approach.

Can I stop treatment early if my animal seems better?

No. Completing the full prescribed course is essential, even if symptoms resolve earlier. Premature discontinuation can lead to:
- Relapse of infection
- Development of antibiotic resistance
- Incomplete eradication of the causative organism

What are signs of overdose?

Signs of sulfadimethoxine overdose may include:
- Severe vomiting and diarrhea
- Lethargy or depression
- Crystalluria or hematuria (blood in urine)
- Seizures (severe cases)

Action: Contact veterinarian or animal poison control immediately.

Is sulfadimethoxine the same as Albon?

Albon is a brand name for sulfadimethoxine. Generic sulfadimethoxine contains the same active ingredient and is bioequivalent to Albon.

References

  1. Plumb DC. Plumb’s Veterinary Drug Handbook. 9th ed. Wiley-Blackwell; 2018.
  2. Papich MG. Saunders Handbook of Veterinary Drugs. 4th ed. Elsevier; 2016.
  3. Riviere JE, Papich MG. Veterinary Pharmacology and Therapeutics. 10th ed. Wiley-Blackwell; 2018.
  4. FDA Center for Veterinary Medicine. Animal Drugs @ FDA Database. Accessed October 2025.
  5. Boothe DM. Small Animal Clinical Pharmacology and Therapeutics. 2nd ed. Elsevier; 2012.
  6. Giguère S, Prescott JF, Dowling PM. Antimicrobial Therapy in Veterinary Medicine. 5th ed. Wiley-Blackwell; 2013.

Disclaimer

This guide is intended for educational purposes and should not replace professional veterinary advice. Dosage recommendations may vary based on individual patient factors, formulation differences, and regional regulations. Always consult a licensed veterinarian before administering any medication and follow their specific dosing instructions.

Sulfadimethoxine should only be used under the supervision of a veterinarian who can properly diagnose the condition, determine appropriate dosing, and monitor for adverse reactions.

Article Information:
- Medical Review: This article has been reviewed by board-certified veterinary pharmacologists
- Evidence Base: All dosing recommendations are supported by peer-reviewed veterinary pharmacology references
- Last Updated: October 23, 2025
- Next Review Due: April 2026

For questions about sulfadimethoxine dosing specific to your animal, please consult your veterinarian.

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