Some experts consider that treatment should only be stopped if jaundice becomes clinically evident. If clinically significant hepatitis occurs while on TB treatment, then all the drugs should be stopped until the liver transaminases return to normal. If the patient is so ill that TB treatment cannot be stopped, then STM and EMB should be given until the liver transaminases return to normal (these two drugs are not associated with hepatitis). Fulminant hepatitis can occur in the course of TB treatment, but is fortunately rare; emergency liver transplantation may be necessary and deaths do occur. Test dosing for drug-induced hepatitis
Drugs should be re-introduced individually. This cannot be done in an outpatient setting, and must be done under close observation. A nurse must be present to take patients pulse and blood pressure at 15-minute intervals for a minimum of four hours after each test dose is given (most problems will occur within six hours of test dosing, if they are going to occur at all). Patients can become very suddenly unwell and access to intensive care facilities must be available.
The reason for maintaining the patient on INH despite the suspicion of MDR-TB is that INH is so potent in treating TB that it is foolish to omit it until there is microbiological proof that it is ineffective. There are also probes available for isoniazid-resistance (katG and mabA-inhA), but these 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 acidDrugs 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.