FWIW I have been giving my dog HIGH levels of CBD to control his epilepsy for like a year now. I'm talking 250 - 300mg PER DAY.
I once did the math on the cannapet capsules and they came out to approx 5-6mg of CBD each. So I am essentially giving an ENTIRE BOTTLE every day.
CBD does have side effects. Especially at the higher levels, though the do seem less pronounced than traditional medicines. In my own dog I have seen:
Increased Appetite (this is more pronounced when I use products derived from MMJ as opposed to industrial hemp)
Mild sedation (he still has his get up and go, but he is just a bit more mellow - less likely to get off the couch if he knocks the toy he was lightly playing with off)
I saw no side effects in him when he was at the lower levels of CBD most people use (Seizure control just seems to take more of the stuff)
Personally, I would NOT be comfortable using something like zyrtec as a prophylactic for staph. A 2015 study found a link between certain types of antihistamines and LONG TERM cognitive impairment. (Cumulative Use of Strong Anticholinergics and Incident Dementia) and of course with zyrtec in particular there is antihistamine dependence and the crappy side effects that go along with withdrawl when you go off of it.
I can see CBD oil helping, it's a good anti-inflammatory for skin conditions - so less overall itching and less chance of a scratch letting the buggers take hold on the skin. Personally though, I would do a 2 punch combo. Something like CBD oil internally for inflammation and also an essential oil skin and coat conditioner to reduce overall microbe numbers on the skin it's self. Lemongrass oil has been shown effective against MRSA in studies (Evaluation of Topical Gel Bases Formulated with Various Essential Oils for Antibacterial Activity against Methicillin- Resistant Staphylococcus Aureus - M Shukr, GF Metwally)
Look into wondercide's lemongrass formula. Protect against both the invisible bugs and the big ones