The first choice oral antibiotic for patients with an infected leg ulcer is flucloxacillin; if flucloxacillin is unsuitable or the patient has penicillin allergy, recommended alternatives are doxycycline, clarithromycin or (in pregnant women) erythromycin.
Flucloxacillin is a relatively narrow-spectrum penicillin, which has good penetration for skin and soft tissue infections and is effective against Gram-positive organisms. However, it has poor oral bioavailability and people with impaired circulation may need a higher (off-label) dose of up to 1g, 4 times daily.
The second-line antibiotic, guided by culture results when available, is co-amoxiclav; for patients with penicillin allergy the alternative is co-trimoxazole. These have broader-spectrum activity and are more active against Gram-negative organisms than the first-line treatments.
A 7-day treatment course is recommended for most people with an infected leg ulcer. This can be extended if the infection is not improving, particularly for people with poor healing and a higher risk of complications because of comorbidities.
These recommendations are summarised in the quick-reference MIMS table of antibiotic regimens.
For patients who are severely unwell or unable to take oral antibiotics, there are several recommended intravenous antibiotics or combinations of antibiotics.
Signs of infection
NICE says that although most leg ulcers are colonised by bacteria, few are infected - and antibiotics are not beneficial when there is no infection.
Symptoms or signs that should be used to determine if the ulcer is infected include redness or swelling spreading beyond the ulcer, localised warmth and increased pain or fever.
Samples for microbiological testing should not routinely be taken from a leg ulcer at initial presentation, says NICE, given that most leg ulcers are colonised by bacteria, and universal sampling could lead to inappropriate antibiotic prescribing. If the leg ulcer is clinically infected, the most likely causative organism is Staphylococcus aureus, which would be covered by empirical treatment with flucloxacillin.