The effects of tetracyclines and erythromycin on complement activation in vitro.

The effects of tetracycline, minocycline and erythromycin on complement activation in vitro were studied. At concentrations of 100 mg/l or less, these antibiotics did not inhibit the capacity of Propionibacterium acnes to cleave C3 in normal human serum or in serum chelated of Ca2+ allowing complement activation by the alternative pathway alone. The antibiotics had no effect (at 100 mg/l) on total haemolytic activity of complement in normal human serum. This study did not provide evidence to support the hypothesis that the efficacy of these antibiotics in the therapy of inflammatory acne vulgaris can be explained by inhibition of complement activation.