Clarithromycin for Horses: Uses, Dosing & Side Effects

This information is for educational purposes only. Never give your pet any medication without your veterinarian's guidance. Dosing, frequency, and safety depend on your pet's specific health profile.

Clarithromycin is a macrolide antibiotic. In equine medicine, it is used extra-label, which means your vet may prescribe it even though it is not specifically FDA-approved for horses. This is common in veterinary medicine when published evidence and clinical experience support its use.

The drug is valued because it penetrates tissues and cells well, including areas where some bacteria can hide. That makes it especially useful for infections caused by intracellular organisms, most notably Rhodococcus equi in foals. Clarithromycin is usually given by mouth as tablets or an oral suspension.

A key safety point: clarithromycin is generally discussed for foals, not adult horses. Adult horses are much more sensitive to serious macrolide-related gastrointestinal complications, including potentially fatal colitis. Because of that risk, your vet will usually avoid clarithromycin in adults unless there is a very specific reason and close supervision.

The best-known use of clarithromycin in horses is treatment of Rhodococcus equi pneumonia in foals. Current equine guidance still lists clarithromycin as one of the macrolides used for this disease, most often combined with rifampin rather than used alone. Treatment plans are usually based on the foal's age, severity of lung disease, ultrasound findings, tracheal wash results when available, and local resistance patterns.

Your vet may also consider clarithromycin for other susceptible bacterial infections when culture results, tissue penetration needs, and the horse's age make it a reasonable option. Because antibiotic resistance is a growing concern in equine practice, clarithromycin should not be started casually or kept on hand for routine coughs or nasal discharge.

In many foals, the medication is only one part of care. Your vet may also recommend repeat lung ultrasound, bloodwork, fever control, environmental cooling, and careful monitoring for diarrhea or reduced sweating during treatment.

Clarithromycin dosing in horses should always come directly from your vet. A commonly cited equine dose for foals with Rhodococcus equi is 7.5 mg/kg by mouth every 12 hours. In practice, your vet may adjust the exact plan based on the foal's weight, response to treatment, concurrent medications, and whether culture or imaging suggests a prolonged course is needed.

For R. equi, clarithromycin is often paired with rifampin. Treatment commonly lasts 4 to 6 weeks or longer, depending on how quickly clinical signs and lung lesions improve. Stopping too early can increase the risk of relapse, while continuing too long can raise the chance of side effects and resistance.

Give the medication exactly as prescribed. Clarithromycin may be given with or without food, but your vet may suggest giving it with food if stomach upset occurs. If you miss a dose, contact your vet or follow their instructions rather than doubling the next dose. Foals on macrolides also need close observation in warm weather because reduced sweating and overheating can develop during therapy.

The most common side effects are digestive upset, including diarrhea, loose manure, reduced appetite, and abdominal discomfort. In foals, diarrhea may be mild and self-limiting, but it can also become significant enough to need supportive care. If your foal develops worsening diarrhea, depression, poor nursing, or signs of dehydration, call your vet promptly.

Macrolides, including clarithromycin, can also cause anhidrosis or reduced sweating in foals. That matters because a foal that cannot sweat normally may overheat, especially in hot or humid weather. Watch for increased body temperature, fast breathing, weakness, or heat intolerance. Your vet may recommend shade, fans, stall rest during the hottest part of the day, and close temperature checks.

A major safety warning is exposure of adult horses to clarithromycin. Even small accidental exposure can be dangerous because adult horses are at risk for severe, sometimes fatal, antimicrobial-associated colitis. Foals being treated should be handled carefully to reduce contamination of the mare or other adult horses. Rare but serious concerns with clarithromycin in animals and people include liver injury, allergic reactions, and blood count changes, so your vet may recommend monitoring in longer courses.

Clarithromycin has several important drug interactions, so your vet should review every medication and supplement your horse is receiving. The most relevant equine interaction is with rifampin. These drugs are commonly used together for Rhodococcus equi, but rifampin can markedly reduce clarithromycin absorption and lung distribution. Your vet may still choose the combination because of clinical experience and guideline support, but it is not a casual pairing.

As a macrolide, clarithromycin can also affect metabolism and transport of other drugs. Caution is advised with medications such as omeprazole, ranitidine, midazolam, opioids, sildenafil, ketoconazole, fluconazole, and some other CYP- or P-glycoprotein-related drugs. It may also have overlapping effects with other antibiotics that bind the 50S ribosomal subunit, such as chloramphenicol, which can make combinations less predictable.

Tell your vet if your horse is receiving ulcer medications, antifungals, sedatives, pain medications, or any compounded products. Do not start, stop, or combine antibiotics without veterinary guidance, especially in foals with pneumonia where resistance patterns and drug penetration matter.