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Postoperative antibiotics after gallbladder removal do not reduce the risk of infection, researchers reported.

In a randomized trial, the infection rate after cholecystectomy was virtually identical with and without postop amoxicillin and clavulanic acid, according to , of CHU Nord Amiens and the University of Picardie in Amiens, France, and colleagues.

The finding calls into question several sets of guidelines that recommend patients be treated with antibiotics for several days before and after the surgery, Regimbeau and colleagues reported in the July 9 issue of the .

But, they reported, "we did not observe a benefit of postoperative antibiotic treatment on infections for patients with grade I or II acute calculous cholecystitis."

Acute calculous cholecystitis is a common cause of emergency admission to surgical wards, accounting for about one in three cases in the U.S., the researchers noted.

And of the 750,000 cholecystectomies every year in the U.S., about one in five is performed because of acute calculous cholecystitis, they added.

The, the , and the all recommend postsurgical prophylaxis with amoxicillin and clavulanic acid or sulbactam for patients with uncomplicated cases, they noted.

But there is a "dearth of controlled studies demonstrating a benefit" for the additional antibiotics, Regimbeau and colleagues reported.

To help fill the gap, they enrolled 414 patients in 17 medical centers in France who presented with grades I or II acute calculous cholecystitis and who received amoxicillin plus clavulanic acid before and at the time of surgery.

They were randomly assigned to continue the antibiotic therapy for another 5 days or to stop, in an open-label, noninferiority trial conducted between May 2010 and August 2012.

The primary outcome was the rate of surgical site or distant infections at or before the 4-week follow-up visit. If the upper limit of the 95% confidence interval for the absolute difference between the arms was less than 11%, the researchers specified, that would indicate noninferiority.

All told, Regimbeau and colleagues reported, there were 66 postoperative infections, including 35 in the nontreatment group and 31 in the antibiotic group.

An intent to treat analysis showed that the rates were 17% in the nontreatment group and 15% in the antibiotic group, for an absolute difference of 1.93%.

The 95% confidence interval for the difference ranged from minus 8.98% to 5.12%, so that the upper limit was less than the prespecified noninferiority criterion of 11%.

A per-protocol analysis involving 338 patients saw infection rates of 13% in both arms, and again the upper limit of the 95% confidence interval was less than 11%.

Regimbeau and colleagues cautioned that the absence of placebo in the nontreatment arm and the lack of blinding might have "decreased the reliability of our evaluation of the primary outcome and the groups' comparability."

The study provides "important new evidence to better inform surgeons performing cholecystectomy," commented of the University of Cincinnati College of Medicine.

But it suffers from a common flaw in many surgical trials -- lack of blinding, he argued in an accompanying editorial.

Unblinded trials can lead to several forms of bias that affect outcomes, Solomkin noted, even when -- as in the study by Regimbeau and colleagues -- steps are taken to minimize those effects.

Nonetheless, Solomkin argued, "randomized trials, even if blinding is not possible, contribute greatly to evidence-based recommendations for clinical practice guidelines."

The study offers "useful data" that can help manage patients undergoing cholecystectomy, he concluded.