GPs who prescribe antibiotics often rely on their personal preferences and experience at the expense of clinical evidence, new research claims.
The British Pharmaceutical Conference (BPC) in Manchester heard many prescriptions may therefore be unnecessary or inappropriate for patients.
This could then increase the potential for antibiotic resistance and add costs to primary care trusts (PCT), pharmacists at Liverpool John Moores University concluded.
Local PCT guidelines for the specialist antibiotics co-amoxiclav and clarithromycin say these drugs should only be used as first-line treatments for only a few conditions.
But the research found these drugs accounted for 15% of all antibacterials prescribed in the study, and often for conditions not included in the PCT guidelines.
Rachel Aspinall, who led the research, said: "There are serious risks associated with prescribing based on preference and experience - it can lead to the chosen drug being inappropriate or completely unnecessary.
"Inappropriate prescribing can also reduce the effectiveness of antibiotics for patients who may need them in the future, and potentially lead to complete antibiotic resistance.
"So it's important GPs are given more support in prescribing. Pharmacists are experts in medicines, and therefore ideally placed to provide support of this kind to ensure all patients receive the best possible healthcare."