About one in five patients who are prescribed antibiotics during a hospital stay experiences at least one adverse drug event (ADE), which is sometimes not apparent until after they are discharged, new research shows.

Further, in a substantial proportion of cases, the prescribed antibiotics are not clinically indicated, which means the associated ADEs (such as allergic reactions, end-organ toxic effects, or subsequent infection with antibiotic-resistant organisms or with Clostridium difficile) are avoidable.

“We wanted to pursue the current study because … harm that is caused by antibiotics prescribed to hospitalized patients, including the antibiotics they are asked to continue after leaving a hospital, has not been previously evaluated,” lead author Dr. Pranita D. Tamma, who directs the pediatric antimicrobial stewardship program at the Johns Hopkins Hospital, told Reuters Health by email.

To investigate, the researchers conducted a retrospective review of electronic medical records of nearly 1,500 patients (median age 59 years; 51% female). All patients had received antibiotics for at least 24 hours while hospitalized (for a median stay of four days) at general medicine wards at the Johns Hopkins Hospital between 2013 and 2014. ADEs included gastrointestinal, dermatologic, musculoskeletal, hematologic, hepatobiliary, renal, cardiac, and neurologic events occurring within 30 days after patients began taking the drug, as well as Clostridium difficile infections or new multidrug-resistant infections within 90 days.

A total of 1,488 patients admitted during the study period received an antibiotic for at least 24 hours and were included in the analysis. Nearly 80% received more than one antibiotic.

The most common indications for antibiotic treatment were urinary tract infections, skin and soft tissue infections, and community-acquired pneumonia. The most frequently prescribed antibiotics were third-generation cephalosporins, parenteral vancomycin, and cefepime. A fifth of the patients experienced at least one antibiotic-associated ADE, the researchers report in JAMA Internal Medicine, online June 12.

The overall rate of antibiotic-associated ADEs was 22.9 per 10,000 person-days.

Nearly all (97 percent) of the 324 documented ADEs were considered clinically significant because they resulted in new or prolonged hospitalization, additional clinic or emergency department visits, or additional diagnostic procedures. The median length of treatment per patient was seven days. For every additional 10 days of antibiotic therapy, patients experienced a 3% increase in ADE risk.

A total of 287 (19 percent) antibiotic regimens were prescribed to treat conditions for which antibiotics were not indicated, and 56 of these (20 percent) had antibiotic-associated ADEs, the authors noted. Most of the ADEs occurred during hospitalization, but nearly a quarter of them emerged after patients were discharged, including 11 cases of C. difficile and 44 multi-drug resistant infections.