From what I have read, there have been times when certain medications in the feed hurt ducklings because they eat so much more than chicks. I have also read that amprolium is not such a danger to ducklings, but many people would rather not risk it.
So, I would find out exactly what the medication is and then look into what the recommendations are for that with ducklings.
So, I would find out exactly what the medication is and then look into what the recommendations are for that with ducklings.