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Precautions and Side Effects

• While azithromycin is generally safe and effective when prescribed by a veterinarian, it can cause side effects in some animals. Most importantly, azithromycin should not be used in animals with known hypersensitivity or an allergy to azithromycin or other macrolide antibiotics. Note: Other macrolides include clarithromycin, erythromycin, and roxithromycin. If your pet has had a reaction to any of these medications, inform your veterinarian immediately.
• It is important to understand the general principles of antibiotic usage and that frequent or prolonged administration can lead to resistant infections. Your veterinarian will help guide you to what is appropriate for your pet.
• Although azithromycin is commonly used in dogs and cats, it was created for and is licensed for use in humans only. Therefore, most available research focuses on human use and side effects. There is substantial documentation of liver problems including hepatotoxicity and cholestatic jaundice in humans. Additional side effects in humans include hearing abnormalities, taste or smell loss, angioedema, severe diarrhea caused by Clostridium difficile, and aggravation of myasthenia gravis symptoms.
• In dogs and cats, azithromycin should be used with great caution (if at all) when there is a pre-existing hepatic (liver) or renal (kidney) disease and avoided with the failure of these organs. The most common side effects relate to the gastrointestinal tract, such as vomiting, diarrhea, or abdominal pain. Cardiac arrhythmias, including ventricular tachycardia, may be precipitated by azithromycin. Renal dysfunction, including interstitial nephritis and acute renal failure, may occur secondary to azithromycin treatment and liver function may be affected. Eye irritation may occur in pets receiving the ophthalmic formulation. Ergot toxicity may occur when ergotamine or dihydroergotamine are concurrently administered with azithromycin.
• Note: Call your vet for recommendations if you believe your pet is suffering from an adverse reaction.

Drug Interactions

Azithromycin can interact with certain medications that include:

• Azithromycin may elevate serum digoxin levels in cardiac patients taking digoxin. It can also increase serum levels of theophylline and methylprednisolone.
• Azithromycin can cause a decrease in the clearance of triazolam and midazolam, increasing pharmacologic effects.
• Pimozide is contraindicated in patients receiving azithromycin, and vice versa (death may result).
• Animals being treated with cisapride should not be given azithromycin or other macrolide antibiotics.
• Drugs metabolized by cytochrome P450 (e.g., carbamazepine, terfenadine, cyclosporine, hexobarbital, and phenytoin) will have their serum levels elevated by azithromycin.
• Oral antacids reduce the absorption of azithromycin. When used, drugs should be separated from each other by 2 to 3 hours.
• Azithromycin is incompatible with chloramphenicol when given via subcutaneous route.
• Phenobarbital, a common seizure medication, can alter metabolic enzymes, resulting in ineffective azithromycin therapy.
• Other drugs that should be used with caution include sotalol, ondansetron, dolesetron, ketoconazole, itraconazole, and enrofloxacin.
• If your pet is taking any of the medications listed above, discuss the use of azithromycin with your veterinarian. They can help you understand the risk relative to the benefit and if this is the right medication for your pet.

How Azithromycin Is Supplied and Stored

Most veterinary and human pharmacies inventory tablet sizes (250 and 500 mg) and powder for oral suspension (200 mg/5 mL). Other formulations are generally available by special order.

Azithromycin is supplied as:

• Tablets: 250 mg, 500 mg, and 600 mg film-coated oral tablets. Can be stored at room temperature.
• Capsules: 250 mg. Can be stored at room temperature.
• Powder for injection: 500 mg (lyophilized) in 10 mL vials. Stable for 7 days when reconstituted and stored under refrigeration and for 24 hours when stored at or below 86 degrees Fahrenheit.
• Powder for oral suspension: 100 mg/5 mL, 200 mg/5mL, & 1 g/packet. Store between 41- and 86-degrees Fahrenheit.
• Ophthalmic solution: 1% in 2.5 mL bottle. Should be refrigerated and discarded 14 days after opening. For topical use only.
• Toothpaste: Azithromycin toothpastes may be made at compounding pharmacies in strengths that range from 5% to 8.5% in a variety of flavors. For oral use only.

Dosing Information on Azithromycin for Dogs and Cats

• Azithromycin should never be administered without first consulting your veterinarian. It is a prescription product and cannot be purchased over the counter. It may be given with or without food. For pets that suffer from nausea, vomiting, or diarrhea, it is better to give medication with food. If you miss a dose of azithromycin, give the next dose as scheduled. Do not double the dose.
• The dosage recommended for your pet will vary depending upon the underlying condition being treated. For example, it may be dosed at 15 mg/kg twice daily for 7 days in dogs with a coccidiosis infection or dosed at 5 mg/kg once daily for dogs with a Giardia infection.
• While there is a substantial variation in dosages, the usual dosage in dogs is 2.5 to 5 mg per pound (5 to 10 mg/kg) orally once daily for up to 7 days. In cats, the usual dosage is 2.5 to 7.5 mg per pound (5 to 15 mg/kg) orally every 12 to 24 hours for up to 7 days. Some veterinarians may recommend gradually decreasing the frequency to every 3 to 5 days for a series of doses when treating some conditions (such as respiratory infections in cats).
• Again, the dosage and duration of administration depends on the condition being treated, response to the medication, and the development of adverse effects. Be certain to complete the prescription unless specifically directed by your veterinarian. Even if your dog or cat feels better, the entire treatment plan should be completed to prevent relapse.