Effects of a Constant Dose Rate of Terbutaline on Circadian Peak Expiratory Flow, Heart Rate and Systolic Arterial Pressure in Patients with Asthma Exacerbation

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Abstract
The purpose of this study was to investigate the effect of a constant infusion rate of terbutaline on circadian bronchial peak expiratory flow rate (PEFR), heart rate and arterial pressure in patients with asthma exacerbation. Fifteen hospitalized asthmatic patients (6 females and 9 males, mean age 43.3 years, mean weight 67.0 kg) were included in this study. In order to reach the desired plasma concentrations of terbutaline immediately, a pharmacokinetic simulation was done. Based on the predicted values thus obtained, an initial 5-min bolus dose of 2.94 μg/kg was given to all patients at 7 a.m., i.e. at the beginning of the study. Over the following 24 h (7 a.m. to 7 a.m.), 33 μg/kg of terbutaline was infused intravenously at a constant rate with an electric pump. Since severe acute asthma requires corticosteroids, a 40-mg injection of methylprednisolone was given to all patients at 7 a.m. PEFR, heart rate, systolic arterial pressure, side effects and plasma terbutaline levels were recorded at 7 and 10 a.m., 1, 4, 7 and 11 p.m., and 3 and 7 a.m. the following morning. Terbutaline had a significant favorable effect on asthma exacerbation but no circadian rhythm was found in PEFR. Although terbutaline was infused at a constant rate, plasma levels depended on circadian variations.

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