Flucloxacillin in chronic leg ulcers. Penetration of flucloxacillin into chronic leg ulcer exudate and the effect on the bacteria.

The penetration of flucloxacillin into ulcer exudate was investigated in six patients with chronic leg ulcers. The flucloxacillin dosage used was 1 g orally three times daily for three days, and the serum and exudate concentrations were measured repeatedly during a 10 h-period following the first and the seventh dose. All the ulcers were contaminated with (S. aureus) Staphylococcus aureus either in pure culture (three ulcers) or in culture mixed with Gram-negative bacteria (three ulcers). Bacterial counting in the ulcers was performed twice before and twice during the antibiotic treatment. The flucloxacillin concentrations measured in the ulcer exudate were found to be lower than the corresponding serum concentrations. However, the exudate concentrations were found to be above the minimum inhibitory concentration (MIC) for the contaminating S. aureus during an average of 7 h after each dose, and the number of S. aureus during the treatment period was reduced to less than 0.01% of the initial number. The Gram-negative bacteria were not susceptible to flucloxacillin. The number of these bacteria decreased before flucloxacillin treatment but increased again during treatment, probably owing to the changed conditions in the ulcers following the marked decrease in the number of S. aureus.