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

To determine the effect of prophylactic antibiotics on endometrial and endocervical microflora upon diagnosis of postcesarean endometritis.

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.

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).

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.