4-5 days prior: No prescription or over the counter oral antihistamines should be used. These include cold tablets, sinus tablets, hay fever medications, or oral treatments for itchy skin, over the counter allergy medications such as Claritin, Zyrtec, Allegra, Actified, Dimetapp, Benadryl, and many others.
3 days prior: Over the counter sleeping medications (e.g. Tylenol PM) also contain active ingredients that interfere with histamine.
2 days prior: Discontinue nasal and eye antihistamine medications, such as Patanase, Pataday, Astepro, Optivar, or Astelin.
2 weeks prior: Other prescribed drugs, such as amitriptyline hydrochloride (Elavil), hydroxyzine (Atarax), doxepin (Sinequan), and imipramine (Tofranil) have antihistaminic activity. Do not stop taking these medications before consulting with your physician first.