Soumya Swaminathan*
Division of HIV/AIDS, Tuberculosis Research Centre, Chennai 31.*
Pattern of drug resistance among children with TB tends to mirror that found among adults in the same population. Multidrug resistant TB (MDR-TB) is defined as resistance to both Isoniazid and Rifampicin with or without other drugs.

Drug resistant TB in India is mainly due to poor treatment adherence by the patient and poor management by the physicians. Initial drug resistance in adults to Isoniazid is reported to be in the range of 10-15%, for Rifampicin 2-3% and MDR-TB 1-3%. These rates are much higher in patients who have taken prior, irregular treatment. A multicentric study to evaluate a diagnostic algorithm for TB in children in Chennai revealed an Isoniazid resistance rate of 13% and MDR-TB of 3.5% (TRC, unpublished observation). As it is difficult to isolate M. tuberculosis from children with TB, the clue to drug resistance usually comes from the adult contact. Drug resistant TB should be suspected in the following circumstances:
  1. The child is in contact with a known case of drug resistant TB.
  2. The child's adult contact has been on chronic irregular treatment and continues to be sputum positive.
  3. The adult contact died after taking irregular treatment; and
  4. The child shows initial improvement to ATT and deteriorates (clinically and radiologically).

The only definitive way of diagnosing drug resistance is by isolating M. tuberculosis from the sputum/tissue and assessing its susceptibility pattern, which takes up to 12 weeks.

Child contacts of adults with drug resistant TB should be treated according to the drug susceptibility patterns of the M. tuberculosis strain of the source cases unless their own strain's susceptibility testing indicates otherwise. Contact tracing remains of fundamental importance in identifying children at risk.

Therapy for drug resistant TB is successful when at least 2 bactericidal drugs to which the infecting strain of M. tuberculosis is susceptible are given. Exact treatment regimens can be individually tailored to the specific pattern of drug resistance. If this is not available, at least 3 drugs to which the patient is not exposed earlier should be given. Resistance to INH or Streptomycin alone can be managed with standard 4-drug regimen with good results. However when resistance to both INH and Rifampicin is present (MDR-TB), the management is more complicated and requires second line drugs (e.g. Ofloxacin, Ethionamide, aminoglycoside). A standard regimen used is S3 / Ofloxacin, Ethambutol, Ethionamide, Pyrazinamide. The duration of therapy is usually 18-24 months with an injectable drug for the 1st 6 months. Occasionally, surgical resection of the diseased lung or lobe is required.
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