Alcohol Wipe Before Injection?
It's common for people to wipe injection sites in horses with alcohol before inserting the needle. It's so ingrained into some peoples' minds that they may complain if their veterinarian doesn't use an alcohol wipe before injecting. But what does that little swab really do, and is it needed?
Alcohol is a disinfectant and can kill many (but not all) bacteria and viruses. Therefore, wiping an injection site with alcohol could theoretically reduce bacterial counts and maybe reduce the risk of an injection site infection. However, alcohol does not work well in the presence of organic debris (i.e. dirt), and may not (and likely won't in most cases) penetrate through a horse's haircoat down to the skin. The best aspect of alcohol is some situations is wetting down the hair to help see the area you're injecting (for example, when visualizing the vein for an intravenous injection).
The risk of injection site infection is very low in the average horse, and the true benefit of wiping the site with alcohol is unknown. There is no clear evidence that this practice reduces infections. The most serious injection-associated infection, clostridial myonecrosis, is caused by either inoculation of clostridial spores (which are resistant to alcohol) or by spores that are dormant in the muscle tissue. In either case, wiping the skin with alcohol won't help prevent it.
Bottom line: There's no evidence that alcohol wiping is needed, or useful. There's also no reason not to do it, so it's really a matter of personal preference. Not using alcohol wipes is not an indication of poor practice, but a lot of people will use them on the chance that they are effective, knowing that at worst they will do no harm.
More information about clostridial myonecrosis can be found on the equIDblog Resources page.
Clostridial myonecrosis (also called clostridial myositis or gas gangrene) is a very serious infection caused by growth of Clostridium bacteria in muscle. Clostridia are anaerobic spore-forming bacteria, meaning they only grow in environments without oxygen and they can stay dormant in the form of very tough (e.g. difficult to kill) spores. Clostridal spores can be found in healthy muscle. Presumably they enter the bloodstream periodically from the intestinal tract, but aren't able to grow because of the presence of oxygen in healthy muscle. They lie dormant, waiting for the right conditions to start growing - which in most horses never occurs. Clostridial spores can also be introduced into muscle during injections (e.g. vaccines, medications), surgery or trauma.
