Washington: Adverse reaction to antibiotics necessitates as many as 142,000 emergency department visits every year in the US alone, according to a study.

"This number is an important reminder for physicians and patients that antibiotics can have serious side effects and should only be taken when necessary," said study author Daniel Budnitz of the Centres for Disease Control and Prevention (CDC).

Previously, detailed data on antibiotic adverse events were not available. This investigation is based on nationally representative surveillance data to estimate and compare the numbers and rates of adverse events from antibiotics by class, drug, and event type.

Half the visits were for reactions to penicillins and the other half were from reactions to other antibiotics used to treat a wide variety of bacterial infections.

After accounting for how often antibiotics were prescribed, children less than one year old were found to have the highest rate of adverse drug events.

Almost 80 percent of all antibiotic adverse events in the study were allergic reactions, ranging from rash to anaphylaxis, and the remaining 20 percent were caused by errors and overdoses.

Unlike errors and overdoses from other drugs, allergic reactions to antibiotics typically can only be prevented by avoiding exposure to the drug in the first place.

The study draws from the National Electronic Injury Surveillance System-Cooperative Adverse Drug Event Surveillance (NEISS-CADES) project, a sample of 63 hospitals in the US and its territories. NEISS-CADES is a joint effort of the CDC, the United States Consumer Product Safety Commission, and the Food and Drug Administration.

Previous studies have suggested that half of the estimated 100 million antibiotic prescriptions written in the community setting each year for respiratory tract infections may be unnecessary.

"For conditions in which antibiotics have questionable benefit, such as many mild upper respiratory tract infections, weighing the benefits of antibiotics with the risks of a serious adverse event will be especially important," said Budnitz.

These findings will appear in the Sep 15 issue of Clinical Infectious Diseases. IANS