I don't take Promacta, so I can't give you advice based on that. However, there are so many options when it comes to Medicare insurance and so many price levels, what works for one person won't work for all.
Will you be using standard Medicare with a gap policy? Or will you be using a Medicare Advantage all-in-one plan? (Significant money can be saved with an Advantage plan. I love mine.)
Each company that offers gap and/or Advantage plans has its own formulary, which is a list of the drugs they offer. You have to find plans that offer Promacta and then compare the costs. Drugs in a formulary are priced in "tiers"; Promacta is sure to be the highest tier and have the highest cost out-of-pocket. You could ask a company that doesn't include it in their formulary for an exception, but there's no guarantee an exception will be granted. If it is, the drug might still might be cost prohibitive depending on your circumstances.
I'm glad I don't have to compare plans. It seems so daunting. But I
think there are Medicare counselors that help people with that. I'm just not sure how to find one. I would start by asking a local pharmacist for help. If that failed, I'd go directly to Medicare or perhaps AARP for advice. I know there are people that can help with these choices, but I haven't had the need to find one myself.
Three links that have basic advice that may help you:
1.
www.medicare.gov/drug-coverage-part-d/what-medicare-part-d-drug-plans-cover
2.
www.marketwatch.com/story/how-to-compare-medicare-part-d-plans-01600353975
3. Contact info for Medicare ~
www.medicare.gov/talk-to-someone
