My son is 3 years old and started taking miralax (as per his doctor) on Thursday. Yesterday (Saturday) he broke out into hives. Benadryl was given and miralax was stopped. He broke out into hives 3 times today (Sunday) and I had to give him Benadryl again.

No new foods were given, no new detergents, nothing new in his life, except for the miralax. Could it be an allergy to the miralax? If so, how long will it take for the miralax to leave his system?