MDR TB or Drug-resistant tuberculosis is an emerging problem because of the non-adherence to drugs, long treatment courses, intolerance to and adverse effects of anti-tuberculous medications, HIV epidemics and naturally developing mutants and resistant strains.
This article will focus on some important definitions commonly used in drug-resistant tuberculosis. For the sake of simplicity, the following very important aspects of MDR treatment will be discussed later:
- When to suspect an MDR TB organism?
- How to build an MDR treatment regimen?
- Treatment of MDR TB in special circumstances.
Important definitions in MDR TB.
Monoresistant Tuberculosis:
Mycobacterium Tuberculosis organisms resistant to any first line anti-tuberculosis drug.
2. Polyresistant Tuberculosis:
Resistance to more than one first-line anti-TB drug, other than both isoniazid and rifampicin.
3. Rifampicin Resistant Tuberculosis (RR-TB):
Mycobacterium Tuberculosis resistant to Rifampicin. Patients with RR-TB are eligible to be treated with the MDR-TB regimen.
4. Multidrug Resistant Tuberculosis (MDR-TB):
Mycobacterium Tuberculosis resistant to both Isoniazid and Rifampicin
5. Extensively drug resistant tuberculosis (XDR-TB):
Mycobacterium Tuberculosis organisms resistant to both Isoniazid and Rifampicin (i.e. MDR-TB) plus resistance to any fluoroquinolone, and at least one of three second-line injectable drugs (capreomycin, kanamycin, and amikacin).
Definition of treatment outcomes in Drug resistant tuberculosis:
1. Cured:
Patients who complete the full course of anti-tuberculous therapy without evidence of a failure AND three or more consecutive cultures taken at least 30 days apart are negative after the intensive phase.
2. Treatment completed:
Treatment completed as recommended without evidence of failure BUT no record that three or more consecutive cultures taken at least 30 days apart are negative after the intensive phase
3. Treatment failed:
Treatment terminated or need for permanent regimen change of at least two anti-TB drugs because of:
a. Lack of conversion by the end of the intensive phase; or
b. Bacteriological reversion in the continuation phase after conversion to negative; or
c. Evidence of additional acquired resistance to fluoroquinolones or second-line injectable drugs; or
d. Adverse drug reactions.
4. Died:
A patient who dies for any reason during the course of treatment
5. Lost to follow up:
A patient whose treatment was interrupted for two consecutive months or more.
6. Not evaluated:
A patient for whom no treatment outcome is assigned. (This includes cases “transferred out” to another treatment unit and whose treatment outcome is unknown).
7. Conversion (to negative):
Culture is considered to have converted to negative when two consecutive cultures, taken at least 30 days apart, are found to be negative. In such a case, the specimen collection date of the first negative Culture is used as the date of conversion.
8. Reversion (to positive):
Culture is considered to have reverted to positive when, after an initial conversion, two consecutive cultures, taken at least 30 days apart, are found to be positive. For the purpose
Definitions of Tuberculosis patients during registration:
1. New Patient:
A patient who has received no or less than one month of anti-TB treatment
2. Relapse:
A patient who was previously treated for TB and whose most recent treatment outcome was Cured or Treatment completed, and who is subsequently diagnosed with a recurrent episode of TB (either a true relapse or a new episode of TB caused by reinfection).
3. Treatment after lost to follow-up.
A patient who had previously been treated for TB and was declared Lost to follow-up at the end of the most recent course of treatment. (This was previously known as the treatment after default).
4. After the failure of first treatment with first-line drugs.
A patient who has received first-line drug treatment for TB and in whom treatment has failed.
5. After the failure of the retreatment regimen with first-line drugs.
A previously treated TB patient who has received a retreatment regimen with first-line drugs and in whom the retreatment has failed.
6. Other previously treated patients.
A previously treated TB patient whose outcome after the most recent course of treatment is unknown or undocumented.