People suffering from a common cold with a persistent runny nose should not initially be prescribed antibiotics, researchers say.

Most current guidelines recommend against the use of antibiotics for the condition, but the advice was based on one study that showed no effect.

The team from New Zealand reviewed results from seven clinical trials comparing antibiotics with placebo for acute purulent rhinitis — a runny nose with coloured discharge that lasts less than 10 days.

"Most patients will get better without antibiotics," Drs. Bruce Arroll and Tim Kenealy of the University of Auckland concluded after assessing the evidence, benefits and harms of treating and not treating.

Since overuse of antibiotics can spur microbes to become resistant to the drugs, researchers have called on doctors and patients to restrain their use of antibiotics.

Antibiotics probably are effective for acute purulent rhinitis. But at best, for every one who is helped by the antibiotics, six others will show no benefit, the researchers concluded in Friday's issue of BMJ Online First.

Antibiotics can cause harm, seen in side-effects such as vomiting, diarrhea, and abdominal pain. Rashes and hyperactivity are also possible, the team reported.

"Our summation would be to suggest initial management by non-antibiotic treatments or 'watchful waiting' and that antibiotics should be used only when symptoms have persisted for long enough to concern parents or patients," the pair wrote.