The reason for using the order for testing drugs is because the two most important drugs for treating TB are INH and RMP, so these are tested first: PZA is the most likely drug to cause hepatitis and is also the drug that can be most easily omitted. EMB is useful when the sensitivity pattern of the TB organism are not known and can be omitted if the organism is known to be sensitive to INH. Regimens omitting each of the standard drugs are listed below.