Pharmacist Blog: Allergies? Or Medication Side Effect?

Recently, my son was on antibiotics, yet again, for a pretty severe ear infection. On Day 7 of his amoxicillin therapy, he woke up with a rash all over his face, neck, stomach, and back. I stopped his antibiotic abruptly and gave him Benadryl, thinking that would solve the issue, while I waited to hear back from his pediatrician. The rash subsided for several hours until the Benadryl wore off, and then it was back with a vengeance. His face was red, and he couldn’t stop scratching his neck and stomach. I gave him more Benadryl, and the pediatrician confirmed that we had to just wait it out as the antibiotic made its way out of his system. This left me with questions. Was my son allergic to amoxicillin, or was this just a side effect of his medication? 

True Allergies

True allergies can be scary. When you have a true allergy, your immune system is triggered by the “allergen” – whether it be a  medication, a food, an insect bite, or a sting – to go into fight mode.  The immune system releases chemicals that lead to an inflammatory response throughout the body. Once exposed to the allergen, the reaction can take minutes to hours to present and can range in severity. Signs of a severe allergic reaction (anaphylaxis) are hives,  itching, pale skin, low blood pressure, swollen tongue or throat, a  weak or rapid pulse, nausea, vomiting, diarrhea, or dizziness or fainting. Anaphylaxis can be life-threatening and needs to be treated right away. If you have a true allergy, you should do your best to avoid the allergen and always carry an epinephrine autoinjector with you, just in case. 

Medication Side Effects

 And now back to my son’s case. Was his rash an allergic reaction or a side effect of amoxicillin? All medications have side effects, and sometimes these side effects can mimic an allergic response. Many side effects of medications are predictable and usually get better with time, as opposed to an allergy that may continue to get worse with prolonged or repeated exposure. An individual can also get a viral rash while on an antibiotic. These rashes start around Day 5 to 7 of therapy, are not itchy or bothersome, and usually go away within three days whether the antibiotic is discontinued or not. My son did have a delayed rash,  but it was itchy and moved around on his body, which is a sign of hives. He also had a fever, pale skin, and some slight swelling in his face. Due to these symptoms, his pediatrician believes he may have a true allergy to amoxicillin and will be avoiding it in the future! Always consult your medical provider for a diagnosis.