Pharmacy First: Infected Insect Bites

About this service

Infected insect bites and stings are one of the seven conditions covered by the NHS Pharmacy First service.⁵ The pathway applies to children aged 1 year and over and adults, and covers bites and stings from both six-legged insects (such as mosquitoes, gnats, and flies) and eight-legged arthropods (such as spiders, mites, and ticks).

The critical clinical distinction is between a normal inflammatory reaction to a bite (which does not require antibiotics and should be managed with self-care) and a true soft tissue infection (which may qualify for antibiotic treatment under the PGD).¹ Antibiotics are only appropriate when there is clear evidence of infection that has been present or worsening for at least 48 hours after the initial bite, with specific clinical signs present.²

Tick bites are assessed under this pathway but are excluded from antibiotic treatment due to the risk of Lyme disease.¹ Erythema migrans (the characteristic expanding rash of early Lyme disease) should always be recognised and referred to a GP urgently. On darker skin tones it may appear more like a bruise than a classic bullseye pattern.

Who to offer the service to

Include

• Aged 1 year and over
• Bite or sting from an insect or arthropod (mosquitoes, gnats, flies, spiders, mites, or ticks). Tick bites are excluded from antibiotic supply under this PGD; see exclusions below.
• Clear evidence of infection present or worsening at least 48 hours after the initial bite or sting (see infection criteria table)²
• NHS eligibility requirements met

Exclude

• Under 1 year old: outside the Pharmacy First pathway. Refer to GP.
• Pregnancy under 16 years: all antibiotic PGDs in this pathway (4a, 4b, 4c) exclude pregnancy in patients under 16 years. Refer to GP or prescriber.
• Pregnancy aged 16 years or over with penicillin or flucloxacillin hypersensitivity: clarithromycin (PGD 4b) is excluded in pregnancy. Check whether erythromycin (PGD 4c) is locally authorised; if so, erythromycin 500mg four times daily for 5 days may be supplied.⁴ Otherwise refer to GP or prescriber. Note: for pregnant patients aged 16 or over with no allergy, flucloxacillin under PGD 4a is not excluded by pregnancy status alone; clinical judgement and discussion with the patient apply.²
• No clear evidence of infection: initial inflammation around a fresh bite should be managed with self-care. Do not supply antibiotics for a normal inflammatory bite reaction.
• Tick bite (any presentation consistent with a tick bite, or where the tick is still present): do not supply antibiotics under PGD 4a or 4b. Refer to GP. Suspected erythema migrans or systemic features (fever, joint pain, fatigue): refer to GP urgently.
• Erythema migrans (expanding bullseye rash, or bruise-like marking on darker skin tones): refer to GP urgently. Do not supply antibiotics under this pathway.
• Bite or sting that occurred while travelling outside the UK with concern about insect-borne disease (e.g. malaria, tick-borne encephalitis): refer to GP
• Bite or sting from an unusual or exotic insect: refer to GP
• Human bite, animal bite, or scratch: refer to GP
• Bite or sting in the mouth, throat, or around the eyes: refer to A&E urgently (airway or vision at risk)
• Suspected anaphylaxis or angio-oedema: call 999 immediately
• Previous systemic allergic reaction (e.g. angio-oedema or anaphylaxis) to the same type of bite or sting: refer to A&E urgently
• Severely immunocompromised with signs or symptoms of infection (PGD definition includes haematological malignancy, solid organ transplant, high-dose corticosteroids, and biological immunosuppressants): refer urgently to A&E. If severely immunocompromised but no current infection signs: refer to GP.
• Known comorbidity that may delay resolution: peripheral arterial disease, chronic venous insufficiency, lymphoedema, or morbid obesity: refer to GP
• Known liver disease or previous flucloxacillin-associated jaundice: excluded from flucloxacillin (PGD 4a). Previous flucloxacillin-associated jaundice without confirmed hypersensitivity does not qualify for clarithromycin under PGD 4b: refer to GP or prescriber.
• Known MRSA colonisation or infection: refer to GP
• Severe pain out of proportion to the wound (possible toxin-producing bacteria): refer to GP urgently
• Significant collection of fluid or pus requiring drainage: refer to GP
• Numbness or tingling of the affected area: refer to GP
• Puncture wound contaminated with fresh water, sea water, soil, or manure: refer (may need alternative antibiotics or tetanus prophylaxis)
• Failed previous antibiotic course for the same episode: refer to GP
• Inability to absorb or swallow oral medicines: refer to GP
• Systemically unwell but sepsis not suspected: refer to GP or A&E same day
• Sepsis suspected: call 999
• Additional exclusions apply under each individual PGD. Always check the complete PGD 4a, 4b, or 4c before supplying.

How to deliver the service

1. Screen for red flags and urgent exclusions first Before assessing for infection, check for features requiring immediate referral. Suspected anaphylaxis or angio-oedema: call 999 immediately. Bite or sting in the mouth, throat, or around the eyes: refer to A&E urgently. Erythema migrans or suspected Lyme disease: refer to GP urgently (do not treat under this PGD). Systemically very unwell or sepsis suspected: call 999. Severely immunocompromised with signs of infection: refer urgently to A&E. Previous systemic allergic reaction to the same bite type: refer to A&E urgently.
2. Check for tick bites and Lyme disease risk All tick bites are excluded from antibiotic supply under PGDs 4a and 4b due to the risk of Lyme disease, regardless of whether infection signs appear to be present.¹ Erythema migrans is the characteristic rash of early Lyme disease: an expanding erythematous ring, often described as a bullseye pattern, appearing days to weeks after a tick bite. On darker skin tones it may appear more as an expanding bruise-like marking than a red ring. If suspected, refer to GP urgently. Flucloxacillin and clarithromycin are not appropriate for Lyme disease.
3. Confirm the bite is at least 48 hours old and check exclusions Ask when the bite or sting occurred. Bites within 48 hours with redness and swelling may simply reflect normal inflammation, not infection. If the bite is less than 48 hours old and there is no spreading or discharge, advise self-care and ask the patient to return if not improving after a further 48 hours. Check for liver disease, previous flucloxacillin jaundice, MRSA, pregnancy, failed previous antibiotic, and the other exclusions listed above. Confirm the relevant PGD exclusion list has been checked in full.
4. Apply the infection criteria Confirm that 3 or more infection signs are present (redness, pain or tenderness, swelling, warmth) AND that there is at least one spreading feature (redness or swelling spreading beyond the bite site, or pustular discharge present).² Draw a line around the border of the erythema at assessment and document its extent in the clinical record.
5. Select the antibiotic and check interactions Flucloxacillin (PGD 4a) is first line.² Before supplying, check for methotrexate (any dose: do not supply flucloxacillin if the patient is taking methotrexate), probenecid, and voriconazole (must not supply under PGD 4a). Check for warfarin use (INR monitoring advised). For penicillin or flucloxacillin hypersensitivity, use clarithromycin (PGD 4b v1.1) if not pregnant.³ For pregnant patients aged 16 or over with penicillin hypersensitivity, check if erythromycin (PGD 4c) is locally authorised.⁴ Key clarithromycin contraindications: QT-prolonging medicines (sotalol, haloperidol, pimozide), simvastatin, lovastatin, lercanidipine, ranolazine, colchicine, ticagrelor, oral midazolam, dronedarone. Clarithromycin also raises warfarin INR and increases bleeding risk with direct oral anticoagulants: advise close monitoring. See the full PGD for the complete interaction list. Counsel on taking flucloxacillin on an empty stomach: 1 hour before food or 2 hours after food. Clarithromycin can be taken with or without food.
6. Counsel and safety net Advise: avoid scratching, keep fingernails short and clean, keep hands clean when touching the area. Skin redness and itch may take up to 10 days to fully resolve even after completing antibiotics. Safety netting: seek medical help immediately if infection spreads further, symptoms worsen rapidly at any time, new symptoms develop (fever, severe pain, red streaking away from the bite site, or swelling of face or throat), or signs of sepsis appear. Seek review if symptoms have not started to improve within 48-72 hours of starting antibiotics.¹ Document the erythema border drawn at assessment and supply a copy of the documentation record to the patient's GP by the next working day.⁵

Assessment: results and next steps

Infection Criteria: All of the Following Must Apply

Infection must be present or worsening at least 48 hours after the initial bite or sting.^{1, 2} Initial redness and swelling in the first 48 hours is a normal inflammatory response and does not qualify for antibiotic treatment.

Flucloxacillin Doses (PGD 4a v1.1, four times daily, on empty stomach, for 5 days)

Take 1 hour before food or 2 hours after food.² First-line for most patients aged 1 year and over. Pregnancy aged 16 or over is not an exclusion from PGD 4a in the absence of penicillin hypersensitivity; for penicillin-allergic patients or those requiring an alternative in pregnancy, see PGD 4b or 4c tables below. Key exclusions before supplying: methotrexate at any dose (do not supply); voriconazole (do not supply); CKD stage 5 (eGFR below 15 ml/min/1.73m2); oral typhoid vaccine within 3 days before or after supply; inability to absorb oral medicines. Check the complete PGD 4a for the full exclusion and interaction list.

Clarithromycin Doses (PGD 4b v1.1, twice daily, for 5 days) - Penicillin Allergy Only

Use clarithromycin under PGD 4b when flucloxacillin is contraindicated due to penicillin or flucloxacillin hypersensitivity.³ Clarithromycin is excluded in pregnancy entirely: do not use PGD 4b in pregnancy; use PGD 4c (erythromycin) instead if locally authorised. Previous flucloxacillin-associated jaundice without confirmed hypersensitivity does not qualify for PGD 4b: refer to a prescriber. Clarithromycin can be taken with or without food. Key contraindications before supplying: QT-prolonging medicines (sotalol, haloperidol, pimozide), simvastatin, lovastatin, lercanidipine, ranolazine, colchicine, ticagrelor, oral midazolam, dronedarone. Additional PGD 4b exclusions: myasthenia gravis; known prolonged QT interval or cardiac arrhythmia; significant heart disease; severe liver disease; CKD stage 4 or 5 (eGFR below 30 ml/min/1.73m2); electrolyte disturbance (hypokalaemia or hypomagnesaemia). Check the complete PGD 4b for the full interaction and exclusion list.

Erythromycin (PGD 4c v1.1) - Pregnant Patients Aged 16+ with Flucloxacillin Hypersensitivity Only

PGD 4c applies only to pregnant individuals aged 16 years and over where flucloxacillin is not appropriate due to penicillin or flucloxacillin hypersensitivity.⁴ PGD 4c must be locally authorised at the pharmacy before it can be used. Check the complete PGD 4c before supplying. Key exclusions: myasthenia gravis; QT-prolonging medicines (see PGD 4c for full list); digoxin; statins; direct oral anticoagulants; warfarin; severe liver disease; CKD stage 4 or 5.

Self-Care for Non-Infected or Early Bites

Where infection criteria are not met, or the bite is less than 48 hours old, advise self-care and ask the patient to monitor for spreading.¹

Recording and submission

• Complete the consultation record contemporaneously on PharmOutcomes and notify the patient's GP on the same day or next working day.⁵
• Key information to record:
  • Informed consent obtained
  • Patient name, date of birth, NHS number
  • Duration since bite (at least 48 hours confirmed)
  • Site of bite and description of the area including extent of erythema (border drawn at assessment)
  • Infection signs present: which of the four were found and how many
  • Spreading feature confirmed: spreading erythema or pustular discharge
  • Tick bite and Lyme disease risk assessed and excluded
  • Inclusions and exclusions checked: liver disease, MRSA, pregnancy status, allergy status, QT-prolonging medicines, co-morbidities, travel history, bite type, methotrexate use
  • PGD version used (PGD 4a, 4b, or 4c v1.1)
  • Antibiotic supplied: name, strength, dose, frequency, duration, quantity, batch number, expiry date
  • Penicillin allergy status confirmed
  • Drug interactions checked against complete PGD interaction list
  • Self-care advice and safety netting given
  • Referral made if applicable: route used, urgency level, and referral outcome documented

Key takeaways

• Infection must be present or worsening at least 48 hours after the bite, with 3 or more infection signs AND at least one spreading feature (spreading redness or pustular discharge). Bites under 48 hours with redness alone are a normal inflammatory reaction: advise self-care.
• All tick bites are excluded from antibiotic supply under this pathway due to Lyme disease risk. Always check for erythema migrans (which may look like an expanding bruise on darker skin tones) and refer to GP urgently if suspected.
• Flucloxacillin (PGD 4a) is first line. Do not supply if the patient is taking methotrexate at any dose. For penicillin allergy, use clarithromycin (PGD 4b) dosed by weight in children under 12, unless pregnant (clarithromycin is excluded in pregnancy: check PGD 4c for erythromycin). Draw a border around the erythema at assessment and safety-net: return immediately if worsening, or if no improvement within 48-72 hours of starting antibiotics.

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