Multi-drug-resistant tuberculosis classification
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] ; Associate Editor(s)-in-Chief: Ammu Susheela, M.D. [2]
Overview
Classification
Based on the drug susceptibility testing of cinical isolates confirmed to be Mycobacterium tuberculosis, The strains are classified as follows. [1]
| Classification | Description |
|---|---|
| Monoresistance | Strain resistant to any one of the first line anti tubercular drugs |
| Polydrug resistance | Strain resistant to more than one first line anti tubercular drugs. (Other than both rifampicin and isoniazid) |
| Multidrug resistance | Strain resistant to both rifampicin and isoniazid |
| Extensive drug resistance | In addition to the multi drug resistance, strain is resistant to any fluroquinolone and to atleast one of the three second line anti injectable drugs like amikacin, capreomycin and kanamycin. |
| Rifampicin resistance | Using genotypic or phenotypic method, strain has been detected to have resistance to rifampicin with or without resistance to other anti TB drugs. It can include monoresistance, multi drug resistance, poly drug resistance or extensive drug resistance. |
Clinical classification
Clinically drug resistant tuberculosis can be classified into acquired drug resistance and primary drug resistance according to pathophysiology.
Acquired resistance
According to WHO , acquired resistance is defined as the isolation of drug resistant M. tuberculosis from a patient who has been treated for TB for one month or longer. Strains can acquire resistance against anti tubercular drugs in the following conditions.
- Inadequately treated by errors by caregivers in prescribing or administering drugs or supplying a poor quality drug
- Patients not completing the full course of treatment
- Patient receiving only partial treatment.
Such conditions can lead to the bacterial population to live for several months during the course of treatment thereby developing resistance against such drugs.
Primary resistance
WHO defines primary resistanc as the isolation of a drug resistant strain from a patient without a history of previous treatment. When a patient gets infected with strains already resistant to anti tubercular drugs it is called as primary resistance. It could be against one drug of 1st line anti tubercular drugs or many drugs in the first and second line of drugs.
Molecular classification
Unique
The restriction fragment length polymorphism helps in molecular classification of drug resistance into unique strains of drug resistance.
Cluster
The restriction fragment length polymorphism helps in molecular classification of drug resistance into cluster of strains of drug resistance.