and must be done under close observation. A nurse must be present to take patient's 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 drugs should be given in this order: Day 1: INH at 1/3 or 1/4 dose Day 2: INH at 1/2 dose Day 3: INH at full dose Day 4: RMP at 1/3 or 1/4 dose Day 5: RMP at 1/2 dose Day 6: RMP at full dose Day 7: EMB at 1/3 or 1/4 dose Day 8: EMB at 1/2 dose Day 9: EMB at full dose No more than one test dose per day should be given, and all other drugs should be stopped while test dosing is being done. So on day 4, for example, the patient only receives RMP and no other drugs are given. If the patient completes the nine days of test dosing, then it is reasonable to assume that PZA has caused the hepatitis and no PZA test dosing need be done. 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. The order in which the drugs are tested can be varied according to the following considerations: The most useful drugs (INH and RMP) should be tested first, because the absence of these drugs from a treatment regimen severely impairs its efficacy. The drugs most likely to be causing the reaction should be tested as late as possible (and possibly need not be tested at all). This avoids rechallenging patients with a drug to which they have already had a (possibly) dangerous adverse reaction. A similar scheme may be used for other adverse effects (such as fever and rash), using similar principles. Dysbiosis caused by HRZE antibiotic treatment Tuberculosis