During a flare-up of recurrent airway obstruction (RAO), a combination of drugs may provide relief. “You need to get rid of the inflammation with the steroids, and then treat with a bronchodilator to open the air passages that are squeezed shut,” says Amy Johnson, DVM, DACVIM, of the University of Pennsylvania. “For an acute episode, we usually recommend systemic steroids administered either intravenously or in the muscle, or even orally, and bronchodilators.”
Clenbuterol (Ventipulmin) and ipratropium are the two bronchodilators most commonly prescribed for horses, and they are usually administered along with the corticosteroids dexamethasone and prednisolone. This drug protocol has been in use for a long time and is generally considered safe. “If the horse has a very severe, acute problem, dexamethasone is the way to go,” says Laurent L. Couetil, DVM, PhD, DACVIM, of Purdue University. “People worry about laminitis when using steroids, and certainly if you have a horse that has foundered previously, there is more risk. But otherwise it is a very safe drug. I’ve had many horses on dexamethasone over the years and have yet to see one founder. We usually treat them for four or five days with a high dose, to give relief and get them comfortable quickly. Then I switch them to oral prednisolone, and the dose can be decreased over time.”
The corticosteroids are available in inhaled as well as oral or injectable forms; clenbuterol is available as an oral syrup; ipratropium must be inhaled. The oral and injectable medications tend to be cheaper and easier to administer. Inhaled medications require the use of a device—either a nebulizer or an inhaler and mask—that covers one or both of a horse’s nostrils; when a vaporized form of the drug is inserted into the device, the horse breathes it in. Two general types of nebulizers and inhalers are available on the market. Typically, a horse might need to be acclimated to the mask and the process.
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“The aerosolized bronchodilators seem to work more quickly than the oral medication,” says Johnson. “An aerosolized bronchodilator has been shown to improve lung function significantly within about five minutes,
and the oral drugs can’t act that quickly.”
Steroids in pill form are often prescribed but they are also available in an inhaled form. “Dexamethasone works very well in a nebulizer, but the problem is that it is also well absorbed in the lungs, so if you are worried about laminitis, the risk is no different than giving it in the vein or giving it orally. It doesn’t really decrease the side effects,” says Couetil, who prefers intravenous use for acute episodes of RAO. “If a horse is in crisis, having a hard time breathing, there is nothing better than IV dexamethasone to give relief. It will give the quickest response.”
Another corticosteroid that can be used with an inhaler is fluticasone. “This is a human drug and expensive, but works very well,” says Virginia Buechner-Maxwell, DVM, MS, DACVIM, of the Virginia–Maryland Regional College of Veterinary Medicine in Blacksburg, Virginia. “I’ve used it in my own horses, and it’s a safe and effective way to control heaves without exposing their whole body to high levels of corticosteroids.” Studies that have compared the “whole body” effect of administering either oral prednisolone or inhaled fluticasone to RAO horses have shown that inhaled fluticasone is very effective with fewer side effects when compared to medications like oral prednisolone. If the cost is within the owner’s budget, providing inhaled fluticasone is a safer long-term treatment option for RAO horses.
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