Hi Rene,

You can retest ACTH 3 weeks after reaching the target dose.  Waiting until September (which is the height of the rise) is NOT a good idea as at that point you would be 'chasing the rise'.  The idea is to have ACTH well controlled before the rise, not trying to play catch up by trying to bring elevated ACTH in line in the fall.  

Prascend dosage is not based on the size of the equine but on the amount needed to control ACTH.  With Isaac's ACTH already having been elevated in prior testing and quite a bit higher this year I would think he will need to be on a minimum of a .5mg/day dosage but possibly he may need a 1mg/day dosage.  If he were mine I'd get him to at least the .5mg dosage and then retest 3 weeks later. 

Once you do that test you can make a decision then on whether or not he needs a bump up to a full pill per day (1mg).  Do keep in mind that we want to see a PPID positive equine with an ACTH in the upper teens to low 20s outside of the seasonal rise to consider them well controlled. If his next test comes back at 30 that would indicate you're on the right track but still need a dose increase.