Indoramin-induced hypotension. An evaluation during ear, nose and throat surgery

Indoramin, a competitive alpha 1-adrenoceptor antagonist, was administered intravenously to 12 fit patients aged 20-49 years during general anaesthesia with either halothane or enflurane for ear, nose and throat surgery. A mean decrease of systolic blood pressure of 6 mmHg followed the initial dose of 0.1 mg/kg. Systolic blood pressures of 70-80 mmHg were achieved in nine patients using 0.29-4 mg/kg. The maximum effect of every dose was achieved within 3 minutes, with a probable duration of action of at least 30 minutes. Large changes of heart rate did not occur, though there was gradual slowing of the heart during each series of incremental administrations. Junctional rhythm, sometimes with bradycardia and hypotension, occurred in five patients (four in halothane group; one in enflurane group). Because of this, and the greater than ten-fold variation in decrease of blood pressure for a single weight-related dose, indoramin is not recommended for the reduction of blood pressure during halothane anaesthesia.