Effects of prophylactic antibiotics on endometrial flora in women with postcesarean endometritis.

OBJECTIVE: To determine the effect of prophylactic antibiotics on endometrial and endocervical microflora upon diagnosis of postcesarean endometritis.
METHODS: The medical records of patients enrolled in open-label comparative trials of therapeutic antibiotics for postpartum endometritis between 1989 and 1994 were reviewed (n = 682). Endometritis was diagnosed by a standard definition that included fever and localizing signs. Endometrial cultures were obtained by a sheathed injection/aspiration technique. Aerobes and anaerobes were isolated by standard microbiologic techniques. The primary outcome, endometrial and endocervical microflora, was compared in women who received intravenous ampicillin (2 g every 6 hours for 1-3 doses), cephalosporin (2 g every 6 hours for 1-3 doses), or no prophylaxis. Secondary outcomes included the cure of endometritis and the prevalence of wound infection in the three groups.
RESULTS: Four hundred sixty-five of 682 patients (67%) had a cesarean delivery. One hundred fifty-one patients received ampicillin prophylaxis, 100 patients received cefazolin prophylaxis, 18 patients received extended-spectrum antibiotics, and 196 patients received no prophylaxis. Patients who received cefazolin prophylaxis had a significant increase in enterococcus (P < .05) and a significant decrease in Proteus species (P < .05) from endometrial samples. Patients who received ampicillin prophylaxis had a significant increase of Mycoplasma species (P < .05), Klebsiella pneumoniae (P < .0001), Escherichia coli (P = .04), and any aerobic gram-negative rod (P = .003) from endometrial samples. Ampicillin prophylaxis was associated with a decrease in Prevotella bivia (P < .05) and any anaerobe (P < .01). Endometritis cure rates were similar between prophylaxis groups and between prophylaxis and treatment groups. However, the cefazolin prophylaxis followed by cephalosporin treatment was associated with more wound infections (19%) than other prophylaxis and treatment groups, (6%, P < .01).
CONCLUSION: Ampicillin and cefazolin prophylaxis alters endometrial and endocervical microflora of women who develop endometritis. Whereas these changes had no effect on endometritis cure rate (power > 80%), the association between cefazolin prophylaxis followed by an extended-spectrum cephalosporin and wound infection may warrant caution against the use of the combination.