Antibiotic allergic reactions are twice as likely to affect younger patients.

For decades, antibiotics have saved countless lives around the world. They’re also one of the most common prescription drugs. But the widespread use of these drugs has come under scrutiny as more bacteria are becoming resistant to the medications and more is being learned about how the drugs can lead to dangerous side effects.

In a recent study published in the Journal of General Internal Medicine, researchers have found that young adults are twice as likely to end up in the ER due to antibiotic side effects than many older patients, despite older patients having a diminished immune system.

For the study, Dr. Andrew I. Geller of the Centers for Disease Control and Prevention (CDC) and his team used national databases as well as participation from hospitals across the country to describe the burden of antibiotic side effects on emergency departments.

The team looked at an estimated 145,490 adult emergency department visits annually from 2011 through 2015 for antibiotic-related events.

Antibiotics are so common that in 2014, 266 million antibiotic prescriptions were written for outpatients in community pharmacies.

This amounts to 5 prescriptions for every 6 people in the United States.

Antibiotics are the second most common reason for emergency department visits, making up one-sixth of all estimated visits to the emergency department for adverse drug events.

Based on 10,225 cases, Geller found that adults between the ages of 20 and 34 had twice the rate of emergency department visits for adverse effects compared with those age 65 and older.

Almost 75 percent of these adverse events were accounted for by allergic reactions.

The antibiotics most likely to cause adverse events were the famous penicillins as well as quinolones which include the widely used ciprofloxacin (Cipro).

Additionally, another type of antibiotic called sulfamethoxazole/trimethoprim (Bactrim) also accounted for up to 25 percent of estimated ER visits related to adverse effects to antibiotics.

Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center said there’s a reason that younger adults have more adverse effects than older adults. It’s due to immunosenescence — or the natural changes the immune system makes with age.

“As we get older, the immune system becomes less robust, less responsive, and therefore is less apt to create allergic problems as we age,” he told Healthline.

Schaffner relates this to the example of hay fever. When you’re younger, hay fever is more likely to affect your immune system. However, despite persistent exposure, as you get older, your hay fever experience becomes milder.

Similarly, “if you’re younger and you’re exposed to an antibiotic, you’re more likely to have an allergic reaction,” he said. “However, if you’re older, your immune system isn’t as responsive and you, fortunately, are less apt to have an allergic reaction.”

The study authors and Schaffner both agree that if physicians give fewer antibiotics there would be fewer allergic reactions.

Unlike overdoses which can be monitored and prevented by appropriate dosing, allergic reactions can only be prevented by avoiding exposure to the antibiotic itself.

According to the CDC in 2015, 269 million antibiotic prescriptions were filled in outpatient pharmacies. Of these, experts say that 30 percent are unnecessary.

The CDC believes that overprescribing antibiotics puts patients at a needless risk for these dangerous conditions.

With increased prescriptions of antibiotics, at least 2 million people become further infected with antibiotic-resistant bacteria each year. According to the CDC, of these 2 million people, 23,000 people die as a direct result of these infections.

Although not directly measured in this study, Clostridium difficile (C. diff), is a serious and uncomfortable complication of antibiotic use. It can result in diarrhea, abdominal cramping, and in severe cases, dangerous inflammation of the colon.

They also report that “even when antibiotics are needed, prescribers often favored drugs that may be less effective in carrying more risk over more targeted first-line drugs recommended by national guidelines.”

The CDC has created initiatives to educate the public about reducing these effects. They have released the “Be Antibiotics Aware” campaign in an effort to help improve antibiotic prescribing and use.

Clinicians are encouraged to reinforce the downsides of antibiotic use to patients.

For example, many viral illnesses can’t be treated by antibiotics and even common bacterial infections such as bronchitis or sinus infections are often cured naturally with time and don’t usually require antibiotics.

Dr. Rajiv Bahl is an emergency medicine physician and freelance health writer. You can find him at