Short-term adverse effects of antibiotic prophylaxis for open-heart surgery.

A study was made of the incidence of postoperative endocarditis and of septicaemia in early convalescence in 814 consecutive patients undergoing open-heart surgery. The results were related to the prophylactic antibiotic given to "cover" the operation. A subgroup of 150 patients was studied more intensively and the bacterial flora of the tracheal aspirates and catheter tips from these patients have been related to the antibiotics used. The results demonstrate that the use of a narrow spectrum agent (flucloxacillin) is associated with a modest change in bacterial flora at the two sites sampled, but that much more pronounced shifts in flora are found with a more broad spectrum agent (cephradine). The changes in flora have been related to the incidence of septicaemia in early convalescence, which was higher (7.7%) in the cephradine group than in the flucloxacillin group (0.9%). Since the overall incidence of prosthetic infection using flucloxacillin was acceptably low (0.49% of perfusions; 0.56% of valve insertions), it is concluded that narrow spectrum prophylaxis offers the better overall choice, at least until more objective comparisons are made.