Comparison of skin blisters and implanted cotton threads for the evaluation of antibiotic tissue concentrations

The skin blister technique and a new technique using subcutaneously implanted cotton threads for the evaluation of antibiotic tissue concentrations were compared. Six volunteers received 2 g ampicillin and, after at least one week, 1 g of cloxacillin intravenously. Samples of serum, blister fluid and thread fluid were analysed by an agar well diffusion technique. The half-life of ampicillin and cloxacillin was prolonged in blister fluid compared to serum and thread fluid. Our conclusions are that the thread technique might reflect the kinetics of antibiotics in extracellular fluid where the penetration mostly depends on serum protein binding of the drug. The blister technique on the other hand might resemble the conditions in different subcutaneously implanted cages, fibrin clots and even abscesses where factors such as time and volume of the extracellular compartments also strongly influence the distribution of antibiotics.