More than a fifth of GP patients prescribed antibiotics for pneumonia fail to respond to the treatment, a major US study has shown.
Researchers analysed the records of 251,947 non-hospitalised adults given antibiotics for community-acquired pneumonia between 2011 and 2015.
In 22.1% of cases, the initial treatment did not work. Failure was defined as the need for a new prescription, a switch to a different antibiotic, an emergency hospital visit, or admission to hospital within 30 days.
Older patients and those with other conditions in addition to pneumonia were most likely not to respond.
For certain classes of antibiotic, failure rates were higher. More than a quarter of patients prescribed beta-lactams failed to improve.
Dr James A McKinnell, from LA BioMed in Los Angeles, presented the findings at the American Thoracic Society's International Conference in Washington DC.
He said: "Pneumonia is the leading cause of death from infectious disease in the United States, so it is concerning that we found nearly one in four patients with community-acquired pneumonia required additional antibiotic therapy, subsequent hospitalisation or emergency room evaluation.
"Our findings suggest that the community-acquired pneumonia treatment guidelines should be updated with more robust data on risk factors for clinical failure.
"Our data provide numerous insights into characteristics of patients who are at higher risk of complications and clinical failure.
"Perhaps the most striking example is the association between age and hospitalisation.
"Patients over the age of 65 were nearly twice as likely to be hospitalised compared to younger patients when our analysis was risk adjusted and nearly three times more likely in unadjusted analysis.
"Elderly patients are more vulnerable and should be treated more carefully, potentially with more aggressive antibiotic therapy."