A comparison of prophylactic antibiotic regimens against airborne orthopaedic wound contamination

Deep infection remains a major complication of joint replacement surgery de spite advances in theatre design, surgical technique and antibiotic prophyl axis. Major randomized controlled trials to determine the most effective an tibiotic prophylaxis are difficult to construct and interpret. In a convent ional theatre, most orthopaedic intra-operative wound contamination arrives by the airborne route. This paper describes a unique method used to compar e antibiotics against airborne bacteria. Seven antibiotics were incorporate d into blood agar at concentrations equivalent to serum levels. Plates were then exposed to airborne theatre bacteria using a multiple synchronous col lection technique. After incubation, the percentage kill was calculated for each antibiotic. At concentrations equivalent to serum level 1h post i.v. dose, all the antibiotics proved highly effective, with kill rates >95%. Im ipenem and co-amoxiclav significantly outperformed the other antibiotics wi th kill rates of 99.6% and 99.4%, respectively. At trough levels, the antib iotics achieved kill rates from 61% to 97.6%. Future randomized controlled trials comparing large numbers of antibiotics in the setting of an already low infection rate are inappropriate. This technique for comparing antibiot ic prophylaxis in quick, inexpensive and repeatable. The superiority of imi penem is not unexpected, but of more interest is the effectiveness of co-am oxiclav over the presently favoured cefuroxime. (C) 2001 The Hospital Infec tion Society.