I was taking formoterol (in a spray) in the same time as clarithromycin (twice a day). now i'm worried about prolonged qt but i feel very well. should i be frightened? my heart was always healthy.

Not usually: Although Clarithromycin may cause problem for people with prolonged QT, the incidence is quite low. If you don't have this EKG finding, don't worry about it. Millions have used this combination without any adverse effect but it is good that you are aware of this potential problem. Clarithromycin does not work on a viral infection. If you have asthma exacerbation, you need more than formoterol.

EKG: This worry can be resolved easily with checking your QT interval on EKG. Also, if you have stopped these medicines, then your QT should be normal now. Check your family history to find if anyone had sudden cardiac problems among parents, uncles, aunts, cousins or grandparents.

Yes!!: Both drugs(and Zithromax) can cause QT prolongation(^QT) individually and the combination is dangerous. If a healthy patient takes 1 medication that can ^QT the risk is quite low. But taking 2 meds that ^QT can be fatal. DON'T TAKE THE COMBINATION!(but inform your Dr). Antibiotics that don't ^QT includeAugmentin,Cephalosporins,Doxycycline. Cipro (ciprofloxacin) ^QT, but less than Levaquin.**see comments below