I don't know why you would take both. Promethazine is another form of medication for nausea and it's side effects are HORRIBLE. Zofran is a first class drug (I've been using it for several months) and I don't see any reason for you to be on both. I would definitely question your doctor and demand some form of explanation. Plus always remember, just because it is prescribed, doesn't mean you have to take it. You would (if you haven't already) probably get a notice from your pharmacy telling you that you are taking two drugs that do the same thing. If you can take just Zofran, I highly recommend it and if you need to adjust the dose it can be raised. Hope that helps. Doctors are pill crazy...
Always ask the pharmacist, they are your best informer on this type of issue.
It can cause a heart issue. I will send you the link in your inbox to see for yourself if you feel you should or not.