I think that most patients do not understand medication allergies very well. Wrongly thinking that you are allergic to certain medications can limit the choices your doctor has in deciding which the best medicine for your current condition is. You could be given a costlier or less effective medication if you incorrectly state that you are allergic to a particular drug.
It is important to know the difference between an allergic reaction to a medicine and a side-effect from a medication. Some patients have been erroneously told by their doctors that a medicine caused an allergic rash when in reality the rash was caused by the underlying illness that the medication was prescribed for. Your doctor should know about any medicine that you have had an allergic reaction to or a side-effect from and should be able to differentiate between the two.
An allergic reaction to a medication occurs when your body's immune system reacts to a drug. The symptoms can include itching and a generalized rash. In severe cases an anaphylaxis allergic reaction occurs which can lead to life-threatening breathing and circulatory troubles.
The allergic reaction can occur even with medications that have been used without problems in the past. Once it occurs the medication will always cause reactions in the future, oftentimes escalating in the severity, unless an allergist desensitizes you to that particular drug by giving you tiny incremental amounts over several months. It will recur with medicines in the same class and sometimes with closely related medications. Just because a family member had an allergic reaction to a certain medication, doesn't mean that you will.
A side effect is not based on your immune system's response to a medication. It most commonly includes nausea, headaches, and drowsiness but can include many other symptoms such as dizziness and taste disturbance. These side-effects are annoying but seldom dangerous.
The side effect might improve with a dose adjustment or just over time with continued use of the same dose. It will usually recur if the same medicine is given in the future. It will sometimes occur with similar medicines but often is specific to a certain drug.
A common mistake a patient will make involves refusing to take a certain medication because of concerns of either allergic reactions or side effects. Unfortunately our pharmacist friends provide written handouts that are often misleading when it comes to warning patients against taking a particular drug if a prior reaction occurred with a similar but different medication. Three common situations are detailed below.
If you had an allergic reaction to penicillin in the past you are still able to safely take some, if not all, cephalosporins (Keflex, Ceclor, etc.). You and your doctor do need to be extra careful however if your allergic reaction to penicillin in the past was an anaphylactic one.
Many patients say they are allergic to codeine. That almost always means that they have a side effect of nausea and/or vomiting when they take codeine. That does not exclude you from taking hydrocodone for pain or a cough, if it is indicated. While you could coincidentally have a gastrointestinal side-effect from that, it is much less likely.
There is a difference between sulfa and sulfates/sulfites. The former is used as an antibiotic while the latter are included in many medications such as morphine and some diabetes pills. Many patients develop a rash with the antibiotic (much more so than with penicillin in my experience), but very few, if any, of them will have any reaction to the other medications.
You should tell your doctor which medications have given you which symptoms and let him decide if it was an allergic reaction or a side-effect. Only by doing this can you assure yourself of allowing your doctor to choose the most beneficial and cost-effective treatment for your condition.
