The development of drug-resistant TB is often the result of monotherapy i.e.:

• the failure of the health care provider to prescribe a multi-drug regimen proven to be effective


• the failure of the patient to take properly prescribed therapy.

Multiple drugs are always prescribed for TB in order to prevent inadvertent monotherapy and thus protect against development of drug-resistant TB. Other factors that may contribute to development of drug resistance include poor quality anti-TB drugs, malabsorption, and drug-drug interactions leading to low serum levels. Drug-resistant TB may be either primary or acquired. Primary resistance occurs when a patient is infected with a drug-resistant strain of M. tuberculosis. Acquired resistance develops during treatment with an incomplete or inappropriate regimen.