HomeSeveral case series describing Canadian experience with MDR-TB management have been published.54,88–92 In these series, the majority of cases (83-96%) were among foreign-born populations and few patients were HIV-positive (0-24%). The proportion of re-treatment cases varied considerably, from 33-67%. The mean number of first-line drugs to which the patients’ isolates were resistant ranged from 3.2-4.7.
It is important to avoid amplification of drug resistance, as there are few highly effective second-line drugs and one or more drugs are commonly stopped or held during the course of MDR and XDR-TB treatment. Preventing amplification of resistance requires that, if a medication is stopped, it must be replaced by an alternative drug. It is noteworthy that among patients with MDR-TB referred to the National Jewish Medical and Research Center (Denver, Colorado), there were an average of 3.9 physician-treatment errors per patient.121 The most common errors were addition of a single drug to a failing regimen, failure to identify preexisting or acquired resistance and administration of an initial regimen inadequate in number of drugs or duration of therapy, or both — all errors that open the door for amplification of resistance.
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