THE PET PHARMACY By Wendy C. Brooks, DVM, DipABVP Educational Director, VeterinaryPartner.com

(for veterinary information only)

Brand Name: Zithromax

Available as 250 mg, 600 mg tablets and oral suspension

Background

Azithromycin is a semi-synthetic antibiotic of the macrolide class, the same class as erythromycin and tylosin. This class of antibiotics acts to inhibit bacterial protein synthesis by inhibiting a cellular structure called a 50S ribosome, a structure that only certain bacteria have and use to make internal proteins. Because non-bacterial cells, like mammal cells, use a different type of ribosome (called a 60S ribosome), this difference in the ribosome structures can thus be exploited. In other words, macrolide antibiotics will interfere with the 50S ribosome but will have no effect on the 60S ribosome, meaning disruption in protein manufacture for bacteria with no effect on mammal cells.

How this Medication is Used

Azithromycin has activity against many bacterial species including Staphylococcus, Streptococcus, Bartonella henselae, and even Borrelia burgdorferi, the agent of Lyme disease.

Azithromycin is often compared to its cousin, erythromycin, and found to have a longer half life in dogs and cats as well as better absorption of oral dosages.

Side Effects

At higher doses, vomiting has been reported though generally this is felt to be less of a problem than with erythromycin. Azithromycin overdose manifests as diarrhea, vomiting, and abdominal cramps.

Interactions with other Drugs

Macrolide antibiotics interact with cisapride and should not be used together.

Cyclosporine blood levels can increase when azithromycin is used concurrently.

Oral antacids interfere with intestinal absorption of azithromycin after oral dosing.

Concerns and Cautions

Because azithromycin is largely removed from the body via the liver (in bile), normal liver function is needed to remove the drug from the body. If liver function is impaired, dosing adjustments may be required.

The oral suspension should not be refrigerated and spoils after 14 days (and should be discarded after this time)

It is our policy not to give dosing information over the Internet.

Date Published: 1/9/2009 5:36:00 PM