I did the every 4 days but my vet actually said one shot every week for 4 weeks and then once a month. I googled the question and right away found a published article saying the same. I will stick with the majority opinion of every 4 days for now but I am hoping the regiment my vet suggested turns out to be better...save me a lot of money.
We've used the label directions on multiple occasions with good results.
We tried the "periodic doses" and didn't really see any difference (still needed the label dose after several months; that suggests the "periodic doses" are ineffective and a waste of money as this stuff is not cheap).
With any medication the label dose is the dose that the regulators have found to be safe and effective. Going outside that protocol makes you vet. medicine experimental project. This is not necessarily illegal (a vet. can use meds in an "off label" way). But it's still an experiment.