sentences:  This serves as a useful marker for MDR-TB, because isolated RMP resistance is rare (except when patients have a history of being treated with rifampicin alone).If the results of a gene probe ("rpoB") are known to be positive, then it is reasonable to omit RMP and to use SHEZ+MXF+cycloserine.The reason for maintaining the patient on INH 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 (even though isoniazid resistance so commonly occurs with rifampicin resistance).