Aminophylline pharmacokinetics and cardiorespiratory effects during halothane anesthesia in experimental animals

The pharmacokinetics and cardiorespiratory effects of aminophylline during halothane anesthesia are not well established and are the subject of this study. Eleven dogs were anesthetized with 1% halothane in air and given 10 mg/kg of intravenous aminophylline (theophylline ethylenediamine) over 5 minutes. Serum theophylline levels were measured over the next 60 minutes and were found to be in the therapeutic range (10-20 mg/L). Theophylline levels decayed according to a two-component exponential function. The half-time for the fast component was 4.5 minutes, while the slow component half-time was 134.5 minutes. Heart rate increased significantly (p less than 0.05) within 2 minutes following aminophylline, and remained significantly elevated for 60 minutes. Pulmonary capillary wedge pressure and systemic vascular resistance decreased 2 minutes after aminophylline, as did the arterial-mixed venous oxygen content difference. Cardiac index increased 2 minutes following aminophylline. All these changes were transient, and values returned to near control values within 10 minutes after aminophylline. Arterial oxygenation, venous admixture, and physiologic dead space were not significantly (p less than 0.05) altered by aminophylline. No cardiac arrhythmias occurred. Other than a sustained 12% increase in heart rate, and transient hemodynamic changes immediately following its administration, aminophylline in therapeutic doses did not have adverse effects on cardiorespiratory function during prolonged 1% halothane anesthesia in normoxic, eucapnic dogs.