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Clinical clangers: ‘I need antibiotics for this infected insect bite’

Kicking off this new series on scenarios that are commonly mishandled in primary care, we take a look at avoiding inappropriate prescribing for an ‘infected’ insect bite

A 54-year-old man suffered an insect bite on the leg the day before yesterday. He didn’t witness the actual event but had been sitting outside on a sunny evening and he does recall a mild transient discomfort around his ankle, where the reaction is apparent.

He now has an area of reddened, slightly raised and warm skin on his lower leg. He describes this as itchy, and it has enlarged since the original event, but he is otherwise completely well. He has a couple of lesser lesions, one on each leg, one of which is blistering slightly. In a well-intentioned attempt to avoid ‘bothering the doctor’, he consulted a pharmacist, who suggested he might need antibiotics, prompting him to attend the GP.

The reality

Redness around an insect bite does not routinely justify antibiotics

The issue

Insect bites commonly present in primary care, obviously more so in the summer – one survey revealed that GPs see anything from five to 100 cases per year, with a half of respondents seeing 10-20 cases annually.1

Cases present for a variety of reasons, but one of the commonest actual, or perceived, agendas is the patient’s concern that the bite may have become infected and therefore require antibiotics. Anecdotally this is becoming a greater issue in primary care as non-GPs such as pharmacists and nurse-practitioners staff the front-line – prescribers may have less confidence in ‘waiting and seeing’ rather than prescribing, and non-prescribers may simply refer the patient on to the GP. The key question is how clinicians can confidently decide whether a bite has become infected.

The evidence

The answer to the question posed above is that there is no answer. In one of the few community-based papers on the subject, published in the British Journal of Family Medicine1, it is acknowledged that this is a virtually evidence and guideline-free zone. The paper confirms that GPs usually feel these attendances are about fears of infection and showed that a significant number (36%) believe that other healthcare workers create inter-referrals and, possibly, a pressure for antibiotics. But it could offer no conclusions or guidance, as there simply isn’t enough evidence on which to base any.

Avoiding a clanger

In the absence of evidence, GPs will have to rely on what they are very good at – pragmatism and common sense.

The exact pathophysiology varies depending on the insect, but what is clear is that a bite leads to a local inflammatory response causing an area of redness, sometimes with blistering, and itching. These symptoms typically last a few days.

Secondary infection in these lesions – described by most authorities as ‘rare’ – would only become clinically apparent after a couple of days, would tend to cause pain rather than itch, and would progressively increase the inflammatory response, possibly with systemic features. This would seem to be echoed by the GPs in the survey who stated that they considered infection depending on limb condition, duration of reaction and systemic features – with their antibiotic threshold also affected by any comorbidities. Some said they find it helpful to draw a line around the erythema to give objective evidence of spreading erythema (although, of course, a ‘normal’ reaction can get worse before it gets better).


Some would argue that the risks (of complaint or an adverse clinical outcome) are such that they would prefer to err on the side of caution and prescribe antibiotics when in doubt, rather than ‘wait and see’ – though there can, of course, be adverse consequences to unnecessary antibiotics, too.

Also, with Lyme disease in the news, the suggestion that the bite might have been from a tick, or a rash compatible with erythema migrans, will understandably prompt an antibiotic.

Key points

  • There is a lack of clear evidence or guidance for managing insect bites.
  • Antibiotics are almost certainly over-prescribed.
  • A ‘normal’ reaction to a bite may last some days and will feel itchy while the patient remains well – avoid the temptation to prescribe antibiotics in this situation.
  • There is a consensus view that infection might be suggested by worsening erythema, pain rather than itch and systemic features.
  • Other factors – such as comorbidities – might reasonably influence the prescribing threshold.

Dr Keith Hopcroft is a GP in Essex


  1. ‘Insect and tick bite management in general practice’. British Journal of Family Medicine, RCGP overdiagnosis group, July 2019.