Long-Acting Antibiotics Can be Both Wonderful and Wrong

Published Dec. 12, 2013

Giving pets oral medications is not always easy, particular when they have to be administered multiple times a day. The combination of an uncooperative patient and a busy schedule can make missed doses the rule, rather than the exception. When owners are unable to follow the recommended treatment schedule, the pet’s health can suffer.

Therefore, it isn’t too surprising that drug companies see an opportunity in developing medications that have very long durations of action.

An example that is in wide use in veterinary medicine today is the antibiotic Convenia (cefovecin sodium). It is labeled for the treatment of skin infections, wounds, and abscesses in dogs and cats but can also be prescribed off label to treat susceptible infections in other parts of the body (e.g., the respiratory or urinary tract). One injection, given by a veterinarian or veterinary technician, provides up to 14 days of antibiotic therapy, which in many cases eliminates the need for owners to give their pets medications at home.

Zoetis, the makers of Convenia, list the following as “key benefits” of their product:

Professionally administered injection provides an assured course of treatment — no missed or off-schedule doses, no interruption of treatment, no leftover pills.

Reaches peak plasma levels quickly and has a distinctly long half-life.

Provides sustained and uninterrupted therapeutic drug concentrations.

Demonstrated efficacy in treating the most common skin infections in dogs and cats.

Gives owners peace of mind that their pets are receiving the treatment they need without the stress of administering daily oral medications.

Aqueous, non-depot injection for rapid release.

What’s not to like about that? Well, as is almost always the case, any form of therapy has its downsides as well as its upsides. Convenia is a cephalosporin, a class of antibiotics that also includes cephalexin (Keflex), cefadroxil (Cefa-Drops), cefpodoxime (Simplicef) … the list goes on. Many of these products are available as generics and are therefore exceedingly cheap. The same cannot be said for Convenia, especially for big dogs. While the cost of a two week supply of an oral cephalosporin and a single injection of Convenia is similar for cats and small dogs, a Convenia injection for a big dog can easily run over $100 dollars.

Other than cost, are there other potential downsides to using long acting medications like Convenia? I can think of two.

Pets can have adverse reactions to any type of drug. The first thing that a veterinarian will recommend when he or she suspects that a dog or cat is reacting poorly is to stop giving that drug. You can’t do that with a long acting product like Convenia. Once it’s in, it’s in. Like all cephalosporin antibiotics, Convenia can cause vomiting, diarrhea, poor appetite, and sometimes even make at-risk pets more susceptible to seizures.

Convenia doesn’t disappear from the body after 14 days. Sub-therapeutic levels of the medication remain in circulation for approximately 65 days after injection. I worry that this could promote antibiotic resistance.

None of this is to say that Convenia or other long acting products are inherently bad. They certainly have their place, and I routinely prescribe them under appropriate circumstances, say when pilling a “feisty” cat would put an owner’s well-being at risk. But, if giving your pet oral medications is a reasonable option, think twice about going with a long acting injection.