Can you take Flagyl or Levaquin if you're allergic to penicillin?

Yes, more than likely you can. Penicillins are part of a drug class known as Beta Lactam, named after their chemical structure. Flagyl, however, is a Nitroimidazole and Levaquin is a fluoroquinolone. Typically, when you have a penicillin allergy to one penicillin medication, depending on the severity, your doctor won't try you on another penicillin because it is likely that you'll have a reaction to it as well. However, usually, a penicillin allergy is just that- a pen allergy. Most patients who are allergic to penicillins (<1% of patients) will not develop an allergy to other Beta Lactam drugs (or other classes of antibiotics, like fluoroquinolones or Nitroimidazoles). Less the 1% of those who have a penicillin allergy (which is less that 1% of everyone...so we are looking at a VERY small number of people) will have what is called a cross-reaction with other beta lactams such as cephalosporins. And even with penicillin allergies, if you have the reaction as a small child, there is actually a potential to "out grow" the allergy as an adult. With that said, many clinicians prefer to use something other than pens in those patients since the risk still exists...especially if the initial reaction was anaphylactoid in nature. Patients may still develop allergies to the other two drugs in question, but it wil not be related to a penicillin allergy.

Also, note that gastrointestinal side effects alone are not indicative of hypersensitivity reactions (i.e. "allergy"). If only GI side effects are experienced, this is a sign of intolerance. Intolerance is not an allergy and the doctor should continue to administer pens as appropriate drug therapy while counseling the patient on ways to prevent or relieve the discomfort associated with GI side effects.

RPh