Effect of two antibiotics on human granulocyte activities

As part of a study of the effects of antibiotic therapy upon human phagocytes, ampicillin and cefaclor were each administered orally to nine healthy adult subjects in a single dose of 500 mg. There was a significant difference in their effects on neutrophil myeloperoxidase (MPO) (EC.1.11.1.7) activity (P less than 0.05) in that ampicillin depressed, but cefaclor enhanced, the measured enzyme activity. Concomitantly ampicillin decreased but cefaclor increased, the rate of phagocytosis of staphylococci, the effects of the two antibiotics also being significantly different (P less than 0.05). Direct measurements of intracellular killing of staphylococci did not change. In four patients with chronic bacterial infections who had low levels of neutrophil MPO activity, treatment with cefaclor led to a significant increase in the MPO levels to within the normal range. Three patients responded satisfactorily to cefaclor despite having previously filed to respond to antibiotics which were similarly active in vitro against the causative bacteria. These findings lead us to suggest that, in patients with chronic refractory infections, attention must be given to the effect of drugs on the host defences in addition to a careful choice of the most active antibacterial agent.