Ran a quick check on this and the MedlinePlus states as follows: "....Cigarette smoking may decrease the effectiveness of this medication." See
http://www.nlm.nih.gov/medlineplus/d...ml#precautions
That could be the problem. You may want to check with the pharmacy where you filled the prescription (can probably just call) or with the prescribing physician, which ever is available.
This class of drug has an extensive list of contraindications (things not to do and side effects). So I wouldn't delay. Hope this helps.