We would only recommend this as a last resort. Tetracycline can cause seriously upset stomachs and has to be eliminated through the kidneys. It is best to save an antibiotic for when it is really needed. And then always use enzymes and friendly bacteria to reseed the intestinal tract. We also use to spray on cotton balls for cleaning the eye and mouth area as needed.
Some people use powders or corn starch under the eyes and on the moustache.
Corn starch is fine, talc is not advised. Some dogs will tear and react to powders of any sort coming near their eyes. So use your own judgment here. Some people use a baby toothbrush or use their fingers to work the cornstarch in. A plastic bottle with a pointed snipped tip is okay, too.