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DRUG RESISTANCE IN TUBERCULOSIS:Criteria for MDR TB
In the absence of facilities for drug sensitivity are not available,MDR TB can reasonably suspected in the following situations:
Criteria for failure of the retreatment regimen
Persistently positive sputum
If the patient is still smear positive after 2 or 3 months of the retreatment regimen,check carefully that he or she has taken the drugs as prescribed.Non adherence to treatment is the commonest cause of "failure" .However,patients with svere disease may take longer to convert from sputum positive to negative.Treatment should not be changed in such patients.If the number of bacilli in direct smear is less and he/she is improving clinically and radiologically,this is particularly reassuring.
Persistent positivity at 5-6 months makes genuine treatment failure much more likely.Again commonest cause is failure to take the drugs.If you are certain that the patient is taking the drugs,it is highly probable that the bacilli are resistant to all the drugs prescribed.An occasional positive sputum may be due to dead bacilli
Positive cultures at the above times is even more important.If direct smear has become negative ,but culture is still positive,eg at 2-3 months,this may only be a stage towards complete sputum conversion.(Transitional resistance)
Fall and rise phenomenon
Sputum smear initially becomes negative (or even less positive),and then later becomes persistently positive.This indicates failure usually due to eihter the patient having ceased to take the drugs or sometimes to the development of resistance to all the drugs.Culture sensitivity tests must be done if facilities exist.
An individual who is being evaluated for tuberculosis should
be asked about the following risk factors for multidrug-
resistant TB. If the individual has one (1) or more risk
factors, s/he should be considered for anti-tuberculosis
treatment with other medication(s) in addition to isoniazid,
rifampin, pyrazinamide and ethambutol.
Previous, especially incomplete treatment for
Close contact of a person with multidrug-resistant TB.
Previous hospitalizations in a hospital with an
outbreak of a drug-resistant strain of TB (especially if
housed on the ward where the outbreak was occurring).
Despite initial treatment with isoniazid, rifampin,
pyrazinamide, and ethambutol, the individual remains M.
tb culture positive after three (3) months of treatment,
or reverts to having a positive culture after having
initially converted cultures from positive to negative.
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