Answer: The SWORBHP teaching philosophy regarding NTG and ischemic chest pain has always been previous prescribed use. Meaning, the patient at one point had been advised by a health care professional to take NTG for this suspected ischemic discomfort, and the patient had in fact done so without complication.
In the scenario you describe above, you have a patient who has had NTG administered by a physician for chest pain of a presumed ischemic etiology and this was done without complication. As such, the SWORBHP Medical Council would consider this as previous prescribed use and as such would be supportive of the paramedic administering subsequent dosages of NTG as per the medical directive.