I'm taking 18mg Ivermectin for a disseminated infection in tablet form [1 + 1/2 tabs] for usually 7 days, have not tried it for longer yet but have not had any ill effects. Although, Ivermectin can be taken for periods of upto a month at the 12mg dose.
If you are taking the tablets [white 12mg tab] it's best to grind these tabs to powder as there is a tough exterior coating which may not dissolve and pass straight through you although this is not necessary with the equine paste.
Also there should always be break periods with any of these anthelminthic meds to give the liver a chance to detox the drug and it helps the liver if one takes Milk Thistle, it's has kept my liver in check, whilst taking these meds, going by the results of my liver enzyme and WBC tests.