My daughter just accidentally took a second dose of singulair (montelukast) 5mg within an hour of the first. Should we be worried? She is 8.

No harm done. One extra dose of Singulair (montelukast) should have no harmful side effects. Singulair (montelukast) has a wide safety margin so your daughter should have no ill effects. But it is a good opportunity for you to discuss the importance of proper dosing and the possible serious effects of taking too many pills or taking the wrong medication. She is old enough.