Friday, 6 June 2014

Antibiotics and the tragedy of the commons

In the last month or so I seem to have come across a lot of discussion on how to reduce use of antibiotics. The basic claim seems to be that we are entering a worrying stage where antibiotics lose their power to stop common infections. Only by reigning back our use of antibiotics can we avoid falling into the abyss. But how do we reign back our use of antibiotics? It is typical to refer to the tragedy of the commons when exploring the options available to us. Personally, however, I feel the tragedy of the commons is a misleading way of looking at the problem with antibiotics. Let me explain.
           The tragedy of the commons can arise whenever there is a resource that is limited in supply (rivalrous in the jargon of microeconomics) but that can be harvested by anyone (non-excludable). Water, fish, clean air and grazing land are the textbook examples. The tragedy is that we end up overusing the resource because each individual harvests as much as he wants, ignoring the negative effect this has on others. For example, the farmer fully irrigates his land, ignoring that this leaves less water for neighbouring farms. Or, the fisherman catches a boat load full of fish, ignoring that this leaves less fish for other fisherman or future generations.
           Antibiotics seem to fit the tragedy of the commons story. In this case the resource in limited supply is 'infections that can be treated with antibiotics'. The more we use antibiotics, the more drug resistant infections become, and so the smaller is the pool of infections that can be treated with antibiotics. If each individual takes antibiotics ignoring the effect that this has on others then we get overuse of antibiotics.
          If we think of the overuse of antibiotics as resulting from a tragedy of the commons then we have a simple solution. Namely, we need individuals to take into account the effect that their use of antibiotics has on others. One way to do this is through price - if we increase the price of antibiotics then use should fall. Another way is to educate people on the problems of overusing antibiotics with the hope they reduce use for social reasons. The latter approach is the one being favoured by policymakers. But, it also seems optimistic to expect much. Increasing the price of antibiotics would seem a surer way to reduce usage. And probably is best in terms of reducing the use of antibiotics in farming. There seems, however, something inherently wrong about increasing the price of antibiotics for human use. Why?
         In the standard tragedy of the commons story we have complete information - everyone knows the benefits and costs of using the good. The tragedy occurs because everyone harvests too much of the good. Increasing the price of the good looks a good way to reduce use. In the antibiotic case, by contrast, we have incomplete information - it is typically unknown whether the antibiotics will help a person or not. The tragedy occurs because too many people use antibiotics when they should not. Increasing the price of antibiotics is wrong because it penalizes those who need to take the antibiotics.
        The overuse of antibiotics does not, therefore, fit the tragedy of the commons story as well as it may at first appear. In particular, the problem is not so much the negative externality that one person's use of antibiotics imposes on another, but more the incomplete information about whether or not to use antibiotics. If we can solve the problem of incomplete information then we probably solve the problem of antibiotic overuse. And, fortunately, it seems as though science is on top of this problem because new methods are being developed to tell whether a patient needs antibiotics or not. Whether patients will trust to science is a different question.