It's time to call an end to the "complete the course" message for some antibiotics, according to an article in a leading medical journal.
Experts writing in The British Medical Journal (The BMJ) argue that the warning given to patients at the start of treatment is not supported by the evidence.
Professor Martin Llewelyn at Brighton and Sussex Medical School and colleagues say that patients are put at unnecessary risk from antibiotic resistance when treatment is given for longer than necessary, not when it is stopped early.
They say that traditionally antibiotics are prescribed for recommended treatment courses and fundamental to this concept is the notion that a shorter treatment would be more inferior.
They add that for most indications, studies to identify the minimum effective treatment duration simply have not been performed.
The "complete the course" notion ignores the fact that different patients respond to treatments in different ways, they said, adding: "Currently, we largely ignore this fact and instead make indication specific recommendations for antibiotic duration that are based on poor evidence.
"This situation is changing in hospital practice, where biomarkers of treatment response can guide when to stop antibiotic treatment.
"Outside hospital, where repeated testing may not be feasible, patients might be best advised to stop treatment when they feel better, in direct contradiction of WHO (World Health Organisation) advice."
For common bacterial infections no evidence exists that stopping antibiotic treatment early increases a patient's risk of resistant infection, the experts said.
Reducing unnecessary antibiotic use is essential to mitigate antibiotic resistance, they argued, adding that antibiotics are a "precious and finite natural resource" which should be given to each patient with a tailored treatment duration.
They say research is needed to determine the most appropriate simple alternative messages, such as "stop when you feel better".
Commenting on the paper, spokesman for the Royal Pharmaceutical Society and consultant pharmacist Dr Kieran Hand, said: "This opinion article from respected NHS infection experts is a welcome opening of the debate in the UK on the relationship between the length of a course of antibiotics, efficacy and resistance.
"As the researchers have pointed out, further research is needed before the 'finish the course' mantra for antibiotics is changed and any alternative message such as 'stop when you feel better' can be confidently advocated.
"It's important to consider the fate of leftover antibiotics if patients are told to 'stop when they feel better'.
"Patients should be encouraged to return unused antibiotics to a pharmacy for safe disposal rather than putting them in the bin, or even worse, saving them for future use or sharing them with friends and family as this could really contribute towards antibiotic resistance.
"The ideal future scenario would be that the right length of treatment for a specific infection for patients is identified from clinical trials and the exact quantity needed is prescribed and dispensed."
In recent years, there has been a UK drive to raise global awareness of the threat posed to modern medicine by antimicrobial resistance.
If antibiotics lose their effectiveness, then key medical procedures - including gut surgery, caesarean sections, joint replacements and chemotherapy - could become too dangerous to perform.
Around 700,000 people around the world die annually due to drug-resistant infections such as TB, HIV and malaria.
The Government's chief medical officer, Professor Dame Sally Davies, said: "The message to the public remains the same —people should always follow the advice of healthcare professionals. To update policies we need further research to inform them.
"NICE (the National Institute for Health and Care Excellence) is currently developing guidance for managing common infections, which will look at all available evidence on appropriate prescribing of antibiotics.
"The Department of Health will continue to review the evidence on prescribing and drug resistant infections, as we aim to continue the great progress we have made at home and abroad on this issue."