Scott G W
Guy's Hospital, London, United Kingdom.
Ann Acad Med Singap. 1987 Apr;16(2):228-9.
Beta 2 agonists are best administered by inhalation since this route provides maximum therapeutic effect with minimum side effects. Plasma levels are lower and muscle cramps, tachycardia and tremor less common. Inhalation may be carried out by use pressurised inhalers (with various modification if necessary), by a Rotahaler with Salbutamol powder, and by nebulisers. All have their uses. Apart from their immediate bronchodilator effect, it is customary to give Beta 2-agonists routinely before inhalation beclomethasone, and there is evidence that regular use of Beta 1-agonists has a useful suppressive effect. In severe chronic asthma high doses may be indicated and be effective where conventional doses have failed. The introduction of reliable sustained-release preparation of theophylline and its derivatives together with plasma assays theophylline levels has enabled therapy to be optimal and side effects to be lessened. The therapeutic range is a plasma concentration of 10-20 mg/l. There are large individual variations in hepatic clearance of theophylline, which may also be influenced by age, liver disease, drugs and viral infections. Theophyllines are less effective as bronchodilators than Beta 2-agonists but in chronic severe asthma have a place for their additive effect. They are used most frequently to suppress nocturnal asthma and early morning wheezing.
β2 激动剂最好通过吸入给药，因为这种给药途径能以最小的副作用提供最大的治疗效果。血浆水平较低，肌肉痉挛、心动过速和震颤也较少见。吸入可通过使用压力定量吸入器（必要时可进行各种改进）、带有沙丁胺醇粉末的旋转式吸入器以及雾化器来进行。各有其用途。除了其直接的支气管扩张作用外，通常在吸入倍氯米松之前常规给予β2 激动剂，而且有证据表明定期使用β2 激动剂有有益的抑制作用。在严重的慢性哮喘中，可能需要高剂量，且在常规剂量无效时可能有效。可靠的茶碱及其衍生物缓释制剂的引入以及血浆茶碱水平检测使治疗达到最佳效果并减少了副作用。治疗范围是血浆浓度为 10 - 20 毫克/升。茶碱的肝脏清除率存在很大的个体差异，这也可能受年龄、肝病、药物和病毒感染的影响。茶碱作为支气管扩张剂的效果不如β2 激动剂，但在慢性重度哮喘中因其相加作用而有一席之地。它们最常用于抑制夜间哮喘和清晨喘息。
