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 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: