What Is Drug Resistance?

Drug resistance is a decline in effectiveness of a drug as a result of tolerance on the part of a patient or changes to an infectious organism the drug normally treats. It is an ongoing issue that can complicate medical treatment significantly by making it harder for a doctor to find a drug that will work effectively for a patient's condition. Pharmaceutical companies engage in considerable research on drug resistance so they can stay ahead of changing trends and release new products in time to help patients.

In terms of patient tolerance, drug resistance is most commonly seen with drugs active on the central nervous system. Tolerance to medications used in pain management is a common issue with patients who experience chronic pain. As they take the medications, the drugs will grow less effective, and the patient needs to take more, or switch to a higher dosage. This can increase dangers to the patient, as a high dose of an opiate medication can be potentially fatal.

Patients on psychoactive drugs to manage symptoms of mental illness can also experience drug resistance. They will find their medications less effective over time and must increase dosages or change medications. This can also occur with drugs patients use to manage seizure disorders. The drug resistance usually resolves when the patient stops taking the drug, and it may be possible to switch back later, after the body's tolerance has waned.

In the treatment of infectious disease, drug resistance is commonly seen with antibiotic-resistant bacteria. These organisms develop offenses against the drugs used to treat them, like enzymes that can break down antibiotics before they reach the bacteria, or changes to metabolic pathways so the drug has no effect. A patient given antibiotics to treat an infection will not respond and may grow much worse as the bacteria continue to grow and spread.

Management of drug resistance in infectious organisms usually involves prescribing a multi-drug regimen. If one drug doesn't kill the organisms, another will, and the patient will start to respond and get better. Doctors may also run sensitivity tests, where they grow a specimen in culture and treat the culture with medications to see which drugs will kill the organisms. Such testing can add to the costs of treatment but may result in a more satisfactory outcome. The patient will also recover much more quickly, as she won't have to take several rounds of useless medication to find the one that works.