Duration of antibiotic prophylaxis. An experimental study.

An animal wound model was used to evaluate single dose cefazolin, multiple dose cefazolin, and single dose cefonicid in the prevention of wound infection. Incisions made in Swiss-Webster mice were contaminated with either Staph. aureus (1.94 X 10(8) colony forming units) or E. coli (4.39 X 10(8) colony forming units). Five experimental groups were studied. Group I encompassed control animals given saline solution, Group II animals given 10 mg cefazolin preoperatively, Group III animals given 10 mg of cefazolin preoperatively and postoperatively, Group IV animals given 10 mg of cefonicid preoperatively, and Group V animals given 20 mg of cefonicid preoperatively. All medications were given by intraperitoneal injection. Antibiotics were given 1 hour before operation. Postoperative doses were given 4 hours after operation. Incisions were opened 48 hours after surgery and wound bacterial concentrations were determined. After both Staph. aureus and E. coli contamination, each of the four cephalosporin regimens significantly reduced the mean wound bacterial concentrations compared with that of the control animals (p less than 0.001). Each of the four cephalosporin regimens also significantly reduced the number of infected wounds compared with that of the control subjects (p less than 0.001). No significant differences were noted among the four antibiotic regimens with respect to mean wound bacterial concentration or infection rate. In the context of this model, a single dose of cefazolin seems to be equally effective as multiple doses of the drug for surgical prophylaxis. Extended half-life cephalosporins, like cefonicid, do not appear to be more effective than a single dose of cefazolin, which is a much less expensive antibiotic.

Methods of splenic preservation and their effect on clearance of pneumococcal bacteremia.

The intravascular clearance of type 3 Streptococcus pneumoniae was studied in Sprague-Dawley rats. Sham celiotomy was performed on 20 animals while another 20 rats underwent splenectomy. Four weeks later, bacteremia was induced by intraperitoneal (IP) injection of S. pneumoniae. Serial cultures of peripheral blood were obtained. Splenectomy produced significant impairment of intravascular clearance of bacteria compared to that noted among control animals (p less than 0.01). Eighty animals were divided into four equal groups: I--splenectomy, II--50% splenectomy with the upper half left in situ connected to the short gastric vessels, III--50% splenectomy with the lower half left in situ connected to the hilar vessels, and IV--splenectomy with implantation of splenic fragments. Pneumococcus was administered IP 16 weeks later. Rats were killed 6 hours after bacterial challenge. Residual splenic tissue was weighed. There was significantly less splenic tissue in Groups II-IV than noted in sham animals after 16 weeks (p less than 0.01). The type of partial splenectomy did not significantly affect the weight of residual splenic tissue 16 weeks later. Implantation did yield viable splenic tissue, though the amount proved significantly less than that resulting from either type of partial splenectomy (p less than 0.01). Mean bacterial counts with time for short gastric (Group II) and hilar (Group III) remnant animals were significantly different from those for the asplenic (Group I) rats (p less than 0.02 and p less than 0.001, respectively). Animals with splenic implants (Group IV) were not significantly different from asplenic rats (Group I). Animals with hilar splenic remnants proved significantly different from those with short gastric splenic remnants (p less than 0.01). Partial splenectomy offers protection against pneumococcal bacteremia, though preservation of the hilar blood supply affords the most benefit. The utility of splenic implantation remains unproven.

Intraperitoneal splenic implants do not alter clearance of pneumococcal bacteremia.

The effect of intraperitoneal splenic autotransplants was studied in Sprague-Dawley rats. Twenty animals underwent total splenectomy. Splenectomy was performed in another group of 20 rats, after which the spleen was diced into 15 pieces and replaced within the leaves of the small bowel mesentery. Twelve weeks later pneumococcal bacteremia was induced by intraperitoneal injection of 5 X 10(6) Streptococcus pneumoniae. Quantitative blood cultures were obtained from the tail vein 15, 30, 45, 60, 90, and 240 minutes after injection. Mean bacterial counts with time for animals bearing splenic autotransplants were not significantly different from completely asplenic rats. At autopsy, all animals receiving splenic implants were found to have viable splenic tissue among the leaves of the small bowel mesentery. This study shows that even allowing 12 weeks for maximal regeneration, splenic autotransplants fail to significantly alter the clearance of an established bacteremia.

The fate of the left kidney after division of its vein.

The effect of dividing the left renal vein was studied in Sprague-Dawley rats. Immediately after the left renal vein is divided near the renal hilum, the left kidney becomes markedly edematous and dusky. Twenty-four hours later, the kidney remains edematous and boggy. In contrast, the edema that immediately follows division of the left renal vein adjacent to the inferior vena cava is much less dramatic and virtually resolves within 24 hours. When the left renal vein was divided near the hilum simultaneously with right nephrectomy, all animals died within 48 hours. When the vein was divided adjacent to the vena cava with simultaneous nephrectomy, all animals survived. The effect of dividing the renal vein on perfusion of the left kidney was studied in Sprague-Dawley rats using intra-arterial injection of copper pigment. Division of the left renal vein reduced perfusion of that kidney to 68.9 per cent of control levels. This reduction was demonstrated to be totally reversible within 10 days.

A comparison of topical and systemic cefazolin for wound prophylaxis.

An experimental wound infection model was used to compare the effectiveness of topical and systemic cefazolin in the prevention of wound infection. Studies were conducted using both Staphylococcus aureus and Escherichia coli as the contaminating organisms. Regardless of the wound pathogen studied, there were no significant differences between topical and systemic cefazolin with regard to wound bacterial concentrations and the incidence of wound infection.

Protection from postsplenectomy sepsis: Effect of prophylactic penicillin and pneumococcal vaccine on clearance of type 3 Pneumococcus.

The intravascular clearance of type 3 Streptococcus pneumoniae was studied in Sprague-Dawley rats. One hundred animals were divided into the following five equal groups: I--splenic mobilization, II--splenectomy, III--splenectomy plus pneumococcal vaccine, IV--splenectomy plus 50,000 U of penicillin prophylaxis, V--splenectomy plus 300,000 U of penicillin prophylaxis. Bacteremia was induced by intraperitoneal injection of 10(6) type 3 S. pneumoniae. Serial cultures of peripheral blood were obtained. Splenectomy produced significant impairment of intravascular clearance of Pneumonococcus compared to clearance in control animals (P less than 0.01). Neither dose of penicillin, administered prophylactically prior to induction of bacteremia, significantly altered pneumococcal clearance of asplenic animals. Administration of polyvalent pneumococcal vaccine to splenectomized rats resulted in measurable antibody titers. More importantly, such immunization of asplenic animals significantly improved pneumococcal clearance compared to clearance in asplenic, nonimmunized rats (P less than 0.03). Although in both groups I and III animals S. pneumoniae organisms were effectively removed from the peripheral blood, the clearance curves are significantly different (P less than 0.01). This represents the difference between phagocytosis by the reticuloendothelial cells of the liver and those of the spleen.