My 2 yr old was prescribed Singulair yesterday for nasal allergie...

My 2 yr old was prescribed Singulair yesterday for nasal allergies. He has taken Claritin and Zyrtec in the past with no side effects but they were not very effective on the allergies. I gave him his first dose of the Singulair last night at bedtime just as prescribed. He had a fitfully night, but I thought it might just be that it was keeping him awake. I didn't think about reading the side effects before I gave it to him. This morning he was irritable and did not want to stand up to get out of his crib. I left him with my husband while I went out for a short while and when I returned home found that he was still not standing or walking. We could tell that it was his left leg and then realized it was his left ankle specifically that was bothering him. I then decided to read the side effects in the packet and realized that muscle/joint pain is a serious side effect. His doctor told us to not give him any more and to come in to see them this afternoon. He is very irritable and lethargic some and just not himself - all of this after one pill. I'm just glad we realized it so soon. I will certainly not allow any of my kids to take this drug or any like it.