Is there a way to find out if I'm allergic to a medicine before I take it?

No. There is really no way to tell until you take the medicine. Many people take it with no problems. You didnt say what drug you are asking about but I see Sulfa listed in your topics. Have you had any allergic reactions to medications before? What antibiotics have you taken in the past? This can help you tell more about whether or not you can take it but not completely as an allergic reaction to anything can come on at any time. I took Keflex with no problem multiple times but one time taking it I developed a rash so even having taken it before is no guarentee you will not have a reaction. Letting a UTI progress and infect the kidneys is bad news for sure! My cousin ignored a UTI hoping it would get better ended up in the hospital with sepsis and nearly died. In fact several of the nurses told her when she was released that they didnt think she would make it! Take the medicine. If you develope rash quit taking it and notify your Dr. If you develop swelling of the face, eyes, tongue or have difficulty breathing call 911.