Battling Resistance to Antibiotics and Pesticides

An Economic Approach

Ramanan Laxminarayan

• Publisher: Routledge
• Year: 2010
• Topic: Economics
• eBook ISBN:
  9781136524301
• Subtopic: Agribusiness
• Index: Economics

The increasing resistance of bacteria to antibiotics, and pests to pesticides, threatens to undo some of the most remarkable advances made in public health and agriculture during the past century. Though the potential consequences of increased antibiotic and pesticide resistance are far reaching, regulatory efforts to address the problem are at a very early stage. Battling Resistance to Antibiotics and Pesticides moves such discussions forward by presenting cutting edge research and the first comprehensive application of economic tools to analyze how antibiotics and pesticides should be used to maximize their value to society. Laxminarayan and his contributors explore lessons from past experiences with resistance, especially in agriculture. They consider what incentives would be ideal for the individuals who prescribe or apply antibiotics and pesticides, and what would be ideal for the firms engaged in developing and producing these products. The chapters in this groundbreaking book reflect the fact that efforts to combat resistance will require contributions from a broad range of scholars and professionals, representing a broad range of expertise. The analysis demonstrates that, for all these participants, an understanding of economic issues is an essential complement to knowledge of medical or biological factors. The book provides economists with an overview of relevant scientific issues, as well as a variety of analytical approaches to studying the economics of resistance. It offers policymakers detailed analyses of the multiple dimensions of resistance and discusses the future strategies to combat and manage resistance. For professionals in medicine, public health, and agriculture, the book translates the economic approaches into usable guidance for daily practice and decisionmaking.

PART I

Issues of Optimal Management
of Resistance

Chapter 1

Dynamics of Antibiotic Use

Ecological versus Interventionist Strategies To Manage Resistance to Antibiotics

James E. Wilen and Siwa Msangi

This chapter explores some economic and epidemiological implications of alternative disease treatment strategies in an institutional setting such as a hospital or clinic. We modify and generalize the integrated economic/epidemiological model first introduced by Laxminarayan and Brown (2001). Laxminarayan and Brown adapted an epidemiological multicompartment model of treatment and infection from Bonhoeffer and others (1997), a characterization based, in turn, on early twentieth-century population models of disease transmission and infection. Laxminarayan and Brown added an economic objective function that incorporates explicit assessment of the present value of the costs and benefits of accelerated disease reduction caused by treatment. Laxminarayan and Brown derived important qualitative conclusions about how to optimally treat a diseased population, showing how treatment and the corresponding buildup of antibiotic resistance are similar to the fundamental economic problems of optimally exploiting a nonrenewable resource. As Laxminarayan and Brown argued, in a closed system, the population of individuals responsive to or susceptible to antibiotic treatment can be thought of as a resource with positive economic value. Treatment yields a stream of benefits associated with accelerated recovery of the diseased population, but at the same time, antibiotic resistance as a result of treatment leads to a “draw down” of the stock of susceptibility. The optimal treatment decision thus must account for the dynamic trade-off associated with immediate disease reduction gains and long-term future resistance buildup costs.

Our chapter generalizes the Laxminarayan and Brown paper in an important way by including the possibility that there are fitness costs associated with genes that allow a disease to be resistant to antibiotic treatment. Laxminarayan and Brown ignored fitness costs to highlight the analogy with the nonrenewable resource problem. We show that fitness costs affect the optimal treatment regime in two major ways. First, with fitness costs it is possible that the optimal long-run treatment regime involves steady state strategies that hold resistant and susceptible populations in a symbiotic balance, more like a multispecies renewable resource problem than a nonrenewable problem. Second, with fitness costs, it is also possible that ecological (nonantibiotic) strategies that encourage susceptible bacteria to outcompete resistant bacteria are economically preferable to interventionist strategies involving aggressive antibiotic treatment. In the appendix, we solve the general problem explicitly, characterizing long-term steady states and approach paths in terms of fundamental parameters. Our chapter explains the results using modified phase diagrams that characterize the results qualitatively. We also compare the two broad kinds of treatment strategies, categorized as interventionist and ecological, with a numerical model.

This chapter examines some of the economic implications of antibiotic use within a human population and illustrates the implications of relative fitness among different disease vectors on drug resistance in the population. As emphasized throughout this book, the issue of antibiotic resistance is clearly one of the more important contemporary world health issues. Over the past few years, physicians and health care practitioners have come face to face with several virulent strains of drug-resistant diseases. To name just a few, penicillin-resistant gonorrhea; vancomycin-resistant Staphylococcus aureus; and the bacterial species Enterococcus faecalis, Mycobacterium tuberculosis, and Pseudomonas aeruginosa, are all just beginning to evade the reach of the current stockpile of antibiotics. These new resistant bacteria represent a clear and present danger to many in developing and developed countries alike. Much acquired antibiotic resistance has come about as a result of misuse by both physicians and self-medicating individuals, which has induced natural selection pressure favoring the survival of resistant genes within viral and bacterial species. The consequent gradual buildup of drug resistance in the population has put increasing pressure on researchers to develop new treatment agents to keep quickly mutating pathogens in check. Many observers have suggested that the large, front-loaded costs of drug innovation and the long approval lags have slowed this process, however, and knowledgeable insiders suggest that no new “miracle” drugs are on the horizon with wide effectiveness to attack these new resistant strains of disease.

Clearly, policy decisions affecting the supply side of the problem will be critical to the future of disease control because research and development at the pharmaceutical level depend on patent laws, intellectual property rights, and tax and subsidy policies. At the same time, physicians and hospitals are beginning to practice new notions of drug-use management aimed at reducing the buildup of resistance via demand side management. In this chapter, we extend the important optimal antibiotic use work by Laxminarayan and Brown (2001) to include cases in which bacterial populations can be managed when fitness costs are associated with resistance. The Laxminarayan and Brown paper poses a purposefully stark problem in which antibiotic use irreversibly degrades the stock of drug susceptibility. This framework in their modeling structure relies on the assumption that no fitness cost is associated with bacteria that is resistant to an antibiotic drug. In this chapter, we introduce fitness costs, leading to a system in which antibiotic effectiveness can be managed to a steady state. In our setting, antibiotic effectiveness can be regarded as a “renewable” rather than “nonrenewable” resource, opening up opportunities for interesting resistance management trade-offs, including possibilities of management without using antibiotics. We contrast two different regimes. We first discuss the basic epidemiological dynamics under a no-treatment policy, which we refer to as an “ecological” policy. By ecological policy, we mean a noninterventionist policy that allows a disease to progress in a manner dictated by the natural interaction among bacteria exhibiting interspecific and intraspecific competition. We then explore the treatment or “interventionist” regime for which the disease progresses in a manner dictated by interspecific and intraspecific competition that is aided and altered by antibiotic drug treatment. Finally, we compare the outcomes of interventionist and treatment regimes. This comparison is then extended with a discussion of a broader range of nondrug treatment regimes as mechanisms for managing the problem of antibiotic resistance.

Literature Review

Most of the literature that currently exists on the subject of antibiotic resistance is largely within the biological and medical science literature. Optimal human drug use has been addressed within an economic context by only a handful of economists. Among the most notable papers that have dealt with the economic considerations surrounding biological resistance have been those of Hueth and Regev (1974), Brown and Layton (1996) and, most recently, Laxminarayan and Brown (2001).

The Hueth and Regev paper was one of the first papers to examine the economics of resistance buildup. Hueth and Regev examined the problem of pest resistance within an agricultural context and handled the pest management problem in a very general, analytical framework using optimal control theory. They considered the optimal timing of pesticide application over a growing season to maximize crop profits net of pest costs and subject to biological equations of motion for crop growth and susceptibility. They concluded that the gradual depletion of resistance should be anticipated and accounted for as part of an optimal decision and that the timing of pesticide application is important.

The Brown and Layton paper examined both agricultural and human drug use in a very general analytical framework, giving more attention to the private versus public aspect of the problem. By juxtaposing the dynamic optimization problem of the social planner with the myopic and static optimization problem of the private antibiotic user, they showed that the private user treats too much compared with the social optimum of the dynamic optimizer. They also addressed the intergenerational issues that arise with increased resistance over time and discussed the issue of how many people should be treated and who should be treated first. These general discussions give a good overview of the important issues surrounding the socially optimal use of drugs in treating a population and suggest useful directions for further work. At the same time, the paper lacks some of the specificity that can be derived from more explicit epidemiological and econom...

Table of contents

• Front Cover
• Title Page
• Copyright
• About Resources for the Future and RFF Press
• Resources for the Future
• contents
• Contributors
• About This Book
• Introduction: On the Economics of Resistance
• PART I. ISSUES OF OPTIMAL MANAGEMENT OF RESISTANCE
• PART II. THE IMPACT OF RESISTANCE
• PART III. THE BEHAVIOR OF FIRMS
• Index
• About the Editor