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 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 occurs in several classes of pathogens:

• bacteria -- antibiotic resistance
• endoparasites
• viruses -- resistance to antiviral drugs
• fungi
• cancer cells

The most prominent is chemotherapy to attack tumors made of those cells. Resistance to antiviral drugs also occurs in virus populations, notably HIV. When a drug is administered, those organisms which have a genetic resistance to the drug will survive and reproduce, and the new population will be drug-resistant (see natural selection, selection pressure).

In the presence of drugs, pathogens have evolved sophisticated mechanisms to inactivate these compounds (e.g. by pumping out compounds, mutating residues required for the compound to bind, etc.), and they do so at a rate that far exceeds the pace of new development of drugs. Examples include drug resistant strains of Staphylococcus aureus, Klebsiella pneumonia, and Pseudomonas aeruginosa, and Mycobacterium tuberculosis (TB) among bacterium and HIV-1 among viruses. Indeed, no new mutation rates among viruses still outpaces new development. One positive development has been vaccines, which are promising for some bacterial and viral illnesses. But vaccines are not successful in all cases (e.g. in young children), and adequate resources have not been made available.

See also

• multidrug resistance
• antibiotic resistance