Evolutionary consequences of drug resistance: shared principles across diverse targets and organisms

Drug therapy has a crucial role in the treatment of viral, bacterial, fungal and protozoan infections, as well as the control of human cancer. The success of therapy is being threatened by the increasing prevalence of resistance. We examine and compare mechanisms of drug resistance in these diverse biological systems (using HIV and Plasmodium falciparum as examples of viral and protozoan pathogens, respectively) and discuss how factors-such as mutation rates, fitness effects of resistance, epistasis and clonal interference-influence the evolutionary trajectories of drug-resistant clones. We describe commonalities and differences related to resistance development that could guide strategies to improve therapeutic effectiveness and the development of a new generation of drugs.