are less widely available. When sensitivities are known and the isolate is confirmed as resistant to both INH and RMP, five drugs should be chosen in the following order (based on known sensitivities): an aminoglycoside (e.g., amikacin, kanamycin) or polypeptide antibiotic (e.g., capreomycin) PZA EMB a fluoroquinolones: moxifloxacin is preferred (ciprofloxacin should no longer be used; rifabutin cycloserine a thioamide: prothionamide or ethionamide PAS a macrolide: e.g., clarithromycin linezolid high-dose INH (if low-level resistance) interferon-γ thioridazine meropenem and clavulanic acid Drugs are placed nearer the top of the list because they are more effective and less toxic; drugs are placed nearer the bottom of the list because they are less effective or more toxic, or more difficult to obtain. Resistance to one drug within a class generally means resistance to all drugs within that class, but a notable exception is rifabutin: rifampicin-resistance does not always mean rifabutin-resistance and the laboratory should be asked to test for it. It is only possible to use one drug within each drug class. If it is difficult finding five drugs to treat then the clinician can request that high level INH-resistance be looked for. If the strain has only low level INH-resistance (resistance at 0.2 mg/L INH, but sensitive at 1.0 mg/L INH), then high dose INH can be used as part of the regimen. When counting drugs, PZA and interferon count as zero; that is to say, when adding PZA to a four drug regimen, you must still choose another drug to make five. It is not possible to use more than one injectable (STM, capreomycin or amikacin), because the toxic effect of these drugs is additive: if possible, the aminoglycoside should be given daily for a minimum of three months (and perhaps thrice weekly thereafter). Ciprofloxacin should not be used in the treatment of tuberculosis if other fluoroquinolones are available. There is no intermittent regimen validated for use in MDR-TB, but clinical experience is that giving injectable drugs for five days a week (because there is no-one available to give the drug at weekends) does not seem to result in inferior results. Directly observed therapy certainly helps to improve outcomes in MDR-TB and should be considered an integral part of the treatment of MDR-TB. Response to treatment must be obtained by repeated sputum cultures (monthly if possible). Treatment for MDR-TB must be given for a minimum of 18 months and cannot be