Rash when taking desmopressin

[123swim]

Hi, my 10 year old son has been taking desmopressin for his night time accidents. He has a tablet crushed up and mixed with a biscuit because he wont take the desmomelts and this has been the only way he would take tablets....He has always found taking medications difficult. Anyway it seemed like the desmopressin was helping, however he developed a rash over his trunk and legs and the doc thought viral or drug rash. There are no other symptoms apart from he had a mild cold, and she said stop the drug for a period of time. The rash improved and we have restarted the drug and it looks like the rash may be developing again. It develops some days after taking the medication it seems or maybe something else is causing it? I am going to speak to the pharmacist if the rash fully develops but has anyone else experienced this? After googling I havent found much but I did find you are not supposed to mix the tablet with food x