My ex-husband and I have a joint custody agreement (60:40, me:him) that includes 50/50 decision making power in regard to medical care, education, and religion. When we were married we usually agreed about everything related to parenting and care for the kids. My ex-husband has remarried and now many issues that we previously agreed on have become areas of disagreement. The biggest and most pressing issue relates to medical care for the kids. I feel it is important to follow our pediatrician's advice and thereby give the kids vaccinations and medicine when it is prescribed. My ex-husband has developed an alternative view and wishes to pursue alternative therapies at the exclusion of modern medical care. Right now my son has strep throat and is with his father (it is his parenting time). My son's doctor has written a prescription for Penicillin but my ex refuses to start him on the medication, preferring alternative treatments. I am very worried and upset because untreated Strep will keep my son out of school longer and puts him at risk for dangerous complications (scarlet fever, rheumatic fever). Because we have 50/50 power related to medical care have I reached a legal road block for demanding that my son receive proper medication and vaccinations? How difficult is it to make changes to parenting agreements (specifically decision making power)? Does something like this give me recourse for making a change?
Thanks for your help.

Real hard, you will have to hire an attorney and sue in court and prove why it needs to be changed ( unless you want to give up your part of it or unless your ex wants to give up his part of it.

So you go to court, spend 1000's of dollars fighting this,