Effects of antibacterial agents on the complement system

The alteration of serum complement profile following therapy with various antibiotics was studied in 23 hospitalized patients and in 10 human volunteers. Tetracycline, chloromycetin, ampicillin, and streptomycin reduced serum CH50 and C3 levels in the inpatients. Tetracycline administration for three consecutive days in four normal subjects decreased serum CH50, C1q, C3, and C4 levels on day 4. However, these parameters returned to near-normal levels on day 7 following the withdrawal of the drugs. On the other hand, septran administered in six normal individuals for three consecutive days had no significant effect on the complement system. In vitro studies as well as in vitro studies in guinea pigs treated with various antibiotics showed almost parallel results.