if the patient is intolerant to isoniazid (although 2REZ/7RE may be acceptable if the patient is well supervised). The US recommendation is 6RZE with the option of adding a quinolone such as moxifloxacin. The level of evidence for all these regimens is poor, and there is little to recommend one over the other. Regimens omitting rifampicin The UK prevalence of rifampicin (RMP) resistance is 1.4%. It is rare for TB strains to be resistant to RMP without also being resistant to INH, which means that rifampicin-resistance usually means resistance to INH as well (that is, MDR-TB). However, RMP intolerance is not uncommon (hepatitis or thrombocytopaenia being the most common reasons for stopping rifampicin). Of the first-line drugs, rifampicin is also the most expensive, and in the poorest countries, regimens omitting rifampicin are therefore often used. Rifampicin is the most potent sterilising drug available for the treatment of tuberculosis and all treatment regimens that omit rifampicin are significantly longer than the standard regimen. The UK recommendation is 18HE or 12HEZ. The US recommendation is 9 to 12HEZ, with the option of adding a quinolone (for example, MXF). Regimens omitting pyrazinamide PZA is a common cause of rash, hepatitis and of painful arthralgia in the HREZ regimen, and can be safely stopped in those patients who are intolerant to it. Isolated PZA resistance is uncommon in M. tuberculosis, but M. bovis is innately resistant to PZA. PZA is not crucial to the treatment of fully sensitive TB, and its main value is in shortening the total treatment duration from nine months to six. An alternative regimen is 2HRE/7HR, for which there is excellent clinical trial evidence. The 1994 US CDC guidelines for tuberculosis erroneously cite Slutkin as evidence that a nine-month regimen using only isoniazid and rifampicin is acceptable, but almost all of the patients in that study received ethambutol for the first two to three months (although this is not obvious from the abstract of that article). This mistake was rectified in the 2003 guidelines. This regimen (2HRE/7HR) is the first-line regimen used to treat M. bovis, since M. bovis is intrinsically resistant to pyrazinamide. Regimens omitting ethambutol EMB intolerance or resistance is rare. If a patient is truly intolerant or is infected with TB that is resistant to EMB, then 2HRZ/4HR is an acceptable regimen. The main motivator for including EMB in the initial two months is because of increasing