Interventions for Tuberculosis Control and Elimination 2002

to the medications used in patients who have received prior treatment. That
this is the case has been amply demonstrated. 619 An efficacious re-treatment
regimen must encompass at all times, throughout treatment, at least
two drugs to which the organism is still likely to be susceptible. Countries
which do not have access to medications other than the six essential drugs
for patients who might require them must choose a re-treatment regimen
based on these six drugs.
Because isoniazid is always given in the first-line regimen, a patient
failing to respond to the treatment regimen will have a high probability of
already having isoniazid resistance at the outset of treatment. To adhere
to the principle of a re-treatment regimen incorporating at least two efficacious
drugs, neither rifampicin nor ethambutol should have been used as
the sole companion drug with isoniazid at the point of failure (defined as
sputum smear-positive at five months or later), if either of these drugs is
to be effective in a re-treatment regimen. Their use as a sole companion
drug with isoniazid constitutes functional monotherapy in such a patient
and presents a risk that resistance will have developed to the companion
drug (in this case, either rifampicin or ethambutol). This has been the
rationale behind the recommendation of the IUATLD to utilize isoniazid
plus thioacetazone in the continuation phase. Should bacilli resistant to
thioacetazone emerge, re-treatment is still likely to be successful.
This re-treatment regimen proposed by WHO and the IUATLD consists
of eight months of isoniazid, rifampicin, and ethambutol, supplemented
by pyrazinamide during the first three, and streptomycin during the first
two months. This regimen uses the full range of available drugs except
thioacetazone. Such a regimen has a high probability of curing any patient
who does not commence treatment with organisms already resistant to both
isoniazid and rifampicin. Patients with multidrug-resistant strains have,
after taking the re-treatment regimen, an outcome that is not appreciably
better than reported outcomes in the pre-chemotherapy era. 620
Treatment of patients with organisms resistant to isoniazid
and rifampicin
Patients who fail on directly observed treatment containing isoniazid and
rifampicin throughout, i.e., patients failing on a six-month first-line regimen
or the above-mentioned eight-month re-treatment regimen, are more
likely to harbor organisms resistant to both isoniazid and rifampicin (multidrug-resistant
organisms). In most low-income countries such patients are
designated “chronic excretors” whose fate has to be left to the natural course
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