Antimicrobial use in man and animals – are we poles apart?

For the first time in the UK, we have been able to compare the usage of antimicrobials in humans and in animals following the release of a cross-government department report ‘Overview of antimicrobial usage and bacterial resistance in selected human and animal pathogens in the UK: 2004’.

This is important, as the use of antimicrobials in veterinary medicine and thereby in agriculture has frequently been criticised, even since we have banned the use of antimicrobial growth promoters in Europe.

Critical antimicrobials
There is a joint WHO/FAO/OIE meeting in November to look at the availability of ‘critical’ antimicrobials used in man and animals and this report is extremely timely, as there is very little published information available, on which to draw sensible and practical conclusions.

The amount of antimicrobials used in veterinary medicine in the UK, which includes farm animals and companion animals (cats and dogs) was reported as 454 tonnes in 2004.

Human medicine
In human medicine, use in the community i.e. via general practitioners was 330 tonnes and in hospitals in England only, it was 68.7 tonnes.

If these figures are adjusted for population differences the UK hospital use should be about 82.4 tonnes bringing the total usage to 412 tonnes or 91% of the animal use. However, the type of antimicrobial used in farm animals is frequently very different from those used in human medicine (see Figure 1).

Figure 1. Comparison of antimicrobial use in veterinary and human medicine in the hospital and the community.

Farm animal medicine
In farm animal medicine we use a lot of basic tetracyclines, especially chlortetracycline, which is not available as an oral preparation now in human medicine, but only for topical use.

Trimethoprim is usually used with a sulphonamide in a 1:5 ratio in animals, to utilise the synergistic activity of the combination. In man, they use primarily trimethoprim alone and the trimethoprim use is similar for both. Beta lactams, which include penicillin, synthetic penicillins (amoxycillin) and cephalosporins, are hugely important in human medicine, especially in hospital.

However, cephalosporin use in animals is only 7.5% of human use. These more advanced penicillins and cephalosporins are important as they are associated with the selection of methicillin resistance, which is a major problem in UK hospitals.

Aminoglycosides are hardly used in human medicine due to their relative toxicity and have been largely superseded by the cephalosporins and fluoroquinolones, yet they are still commonly used in veterinary medicine.

Fluoroquinolones are widely used in human medicine both in hospitals and in the community because of their high efficacy and relative safety. In veterinary use, it is only 6.8% of the human figure. In the ‘Other’ group, a substantial proportion of the veterinary antimicrobials are due to the pleuromutilins, which are currently not used in human medicine.

Widely used
Generally, in farm animal medicine many of the older antimicrobials are still widely used and are effective, such as penicillin and the tetracyclines. Cost is also an important factor. In companion animals, cost is not always so critical and frequently the more modern and expensive antimicrobials are used.

Overall though, there is very little cross over of use, except possibly in the macrolide group, but they have now been banned as growth promoters. As long as antimicrobials are used prudently and responsibly, is there any need to further restrict their availability for veterinary use as we are poles apart?