How Safe Is Intake Of Clarithromycin Pills?

I was prescribes clarithromycin er 500mg two tablets every 24 hrs. I have taken the 12 hour one at 500mg every 12 hrs before. I do not feel comfortable taking 1000 mg all at once even though it is time released. Can I take just one? Will it help, or will I be wating my time? I was given this because of flu symptoms all week and now swollen glands and little bit of sore throat.