Drug resistance

Drug resistance is the reduction in effectiveness of a drug in curing a disease or improving a patient's symptoms. When the drug is not intended to kill or inhibit a pathogen, then the term is equivalent to dosage failure or drug tolerance. More commonly, the term is used in the context of diseases caused by pathogens.

Pathogens are said to be drug-resistant when drugs meant to neutralize them have reduced effect. When an organism is resistant to more than one drug, it is said to be multidrug resistant.

Drug resistance is an example of evolution in microorganisms. Individuals that are not susceptible to the drug effects are capable of surviving drug treatment, and therefore have greater fitness than susceptible individuals. By the process of natural selection, drug resistant traits are selected for in subsequent offspring, resulting in a population that is drug resistant.

Classification

Drug resistance occurs in several classes of pathogens:

* bacteria—antibiotic resistance
* endoparasites
* viruses—resistance to antiviral drugs
* fungi
* cancer cells

Mechanisms

Sometimes the target molecule of the drug evolves so the drugs won't bind as well. Sometimes the target cells or organisms evolve better enzymes to degrade the drug, or evolve better mechanisms to pump the drug out of the target cells.

Metabolic price

Biological cost or metabolic price is a measure of the increased energy metabolism required to achieve a function.

Drug resistance has a high metabolic price, in pathogens for which this concept is relevant (bacteria, endoparasites, and tumor cells.) In viruses, an equivalent "cost" is genomic complexity.

Other Problems

Drug resistance not only causes metabolic problems but also results in issues concerning what more can be done to help the infected people and what better and more effective ways can be used without any further drug resistance. Respiratory infections, HIV/AIDS, diarrhoeal diseases, tuberculosis and malaria are the leading killers among infectious diseases to this date. Resistance to first-line drugs has been observed in all of these diseases. In some cases, the level of resistance has forced a change to more expensive second or third-line agents. When resistance against these drugs also emerges, the world will run out of treatment options until other options emerge.