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Anti-tussives aka Suppressants (镇咳药) suppress the cough by:

• suppressing the cough center (延脑咳嗽中枢): e.g. codeine (which is narcotic) or dextromethorphan (which is non-narcotic and may be just as effective)

• Inhibiting the cough reflex arc (咳嗽反射弧hu2) in the periphery: any part of this arc: 感受器 - 传入神经 - 反射中枢 - 传出神经- 效应器: e.g. benzonatate or benproperine

• Both: e.g. pentoxyverine

Expectorants (祛痰药): Phlegm is the product of inflammation. It can irritate the respiratory tract, hence causing cough or wheezing. It can also cause the infection to worsen. Expectorants thin the phlegm and make the cough more productive in clearing the tract. There are these types:

• 痰液稀释药: ammonium chloride or guaiphenesin

• 痰液溶解药: acetylcysteine or brombexine

• 酶制剂: e.g.糜蛋白酶(chymotrypsin)可溶解纤维蛋白and坏死组织,hence降低痰液粘稠

• 表面活性剂: e.g.泰洛沙泊(tyloxapol)通过雾化吸入可降低痰液的表面张力而使痰液减少