Prophylactic antibiotics are increasingly being used to counteract the high risk of hospital-acquired infection in colorectal surgery patients, but there is doubt about the most effective timing, duration and route for their administration. Anne-Marie Gle

Around 10 percent of hospital inpatients acquire an infection during the course of their stay sufficient to prolong hospitalisation and increase treatment costs, morbidity and the risk of death. Surgical wound infections account for 23 per cent of all hospital-acquired infections and, due to the high risk of contamination from bacteria present in the bowel, colorectal surgery presents a particularly high risk of infection.

Antimicrobial prophylaxis - the practice of using antibiotics as a preventive measure, prior to the onset of infection - has increased significantly over recent years. However, there has been uncertainty as to which antibiotics are the most effective for this purpose and the most effective timing, duration and route for their administration. Furthermore, the question of the contribution of inappropriate prescribing to the spread of antibiotic resistance requires consideration.

The latest edition of Effective Health Care1 summarises and updates the findings of a systematic review of the effectiveness of different antibiotic regimens in preventing wound infection in patients undergoing colorectal surgery.

Effectiveness of antibiotic prophylaxis

Wound contamination is inevitable and patient resistance often low, so the prophylactic use of antibiotics can play an important part in preventing infection after colorectal surgery. A systematic review undertaken in 1981 concluded that the evidence for the benefits of prophylactic antibiotics in colorectal surgery was sufficient to recommend that no further trials be undertaken in which antibiotics are withheld from control groups. However, a further four trials have been undertaken, all demonstrating a greatly reduced rate of surgical wound infection among those receiving prophylactic antibiotic treatment.

More than 70 different regimens appear to have been tested in over 150 trials, but it has not proved possible to identify from the various findings one particular regimen that could be regarded as optimal. Nonetheless, the fact that certain regimens have been shown to be less effective because of their inadequate coverage of both aerobic and anaerobic bacteria or the inappropriate timing and dosage implies that an effective prophylactic regimen should involve broad spectrum cover and that timing and duration of administration are crucial.

Timing and duration of administration

Since the prophylactic use of antibiotics, by definition, involves administration prior to the onset of infection, it is essential that the concentration of antibiotics in the tissue surrounding the surgical wound is sufficient at the time at which any bacterial contamination might occur.

Regimens which use only a single dose of antibiotics have been shown to be as effective as multiple-dose options and tend to be associated with less toxicity, fewer adverse side effects, and less risk of developing bacterial resistance. They are also less costly. However, the length of time for which antibiotics remains active, and their effective distribution in different tissues varies greatly from one product to another. Such factors, together with the duration of the operation, need to be taken into account when assessing the most effective timing and number of doses required for each distinct antibiotic agent.

Risk factors associated with surgical wound infection

The risk of surgical wound infection increases if the patient's resistance is compromised by, for example, radiotherapy, chemotherapy, diabetes, old age, obesity or weight loss. Other factors associated with increased risk of infection include the duration of the operation, the surgeon's experience and the need for blood transfusion.

Bacterial resistance

There is sound evidence that inappropriate prescribing and over prescribing of antibiotics can contribute to the spread of antibiotic-resistant bacteria. The type and extent of resistance varies between institutions but it has been suggested that the prevention of hospital-acquired infections could help impede the development of such bacteria. To be effective, the choice of prophylactic antibiotic needs to take account of the local presence and prevalence of antibiotic-resistant bacteria. For this reason, the search for the ideal prophylactic regimen needs to be constantly revisited. Universal acceptance of any one particular regimen as the ideal should be avoided.

Future research needs to focus on the cost-effectiveness of different regimens of antibiotic prophylaxis. In the meantime, the available research evidence is sufficient for developing guidelines at a local level involving surgeons, microbiologists and pharmacists, and taking account of local resistance profiles to ensure the most effective use of antimicrobial prophylaxis in colorectal surgery. Guidelines should be kept under constant review to avoid the adoption of any one definitive approach.

REFERENCES

1Effective Health Care vol. 4 (5) October 1998: Antimicrobial Prophylaxis in Colorectal Surgery.

Effective Health Care bulletins provide NHS decision makers with information on the effectiveness and cost-effectiveness of interventions and the delivery and organisation of health care. The Department of Health funds a limited number of bulletins for distribution within the NHS. Enquiries should be addressed to: NHS Centre for Reviews & Dissemination, University of York, York YO1 5DD. Phone: 01904 433634; fax: 01904 433661; e-mail: revdis@york.ac.uk

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