Histamine is an important mediator of immediate hypersensitivity reactions acting locally and causing smooth muscle contraction, vasodilation, increased vascular permeability, edema and inflammation. Histamine acts through specific cellular receptors which have been categorized into four types, H1 through H4. Antihistamines represent a class of medications that block the histamine type 1 (H1) receptors. Importantly, antihistamines do not block or decrease the release of histamine, but rather ameliorate its local actions. Agents that specially block other H2 receptors are generally referred to as H2 blockers rather than antihistamines. H1 receptors are widely distributed and are particularly common on smooth muscle of the bronchi, gastrointestinal tract, uterus and large blood vessels. H1 receptors are also found in the central nervous system. The antihistamines are widely used to treat symptoms of allergic conditions including itching, nasal stuffiness, runny nose, teary eyes, urticaria, dizziness, nausea and cough. Their most common use alone or in combination with other agents is for symptoms of upper respiratory illnesses such as the common cold. The central nervous system effects of antihistamines include sedation and decrease in anxiety, tension and adventitious movements. Antihistamines are typically separated into sedating (first generation) and nonsedating (second generation) forms, based upon their central nervous system effects, the nonsedating agents being less likely to cross the blood-brain barrier. In addition, some antihistamines have additional anticholinergic, antimuscarinic or other actions. The antihistamines are some of the most commonly used drugs in medicine, and most are available in multiple forms, both by prescription and in over-the-counter products, alone or combined with analgesics or sympathomimetic agents. Common uses include short term treatment of symptoms of the common cold, seasonal allergic rhinitis (hay fever), motion sickness, nausea, vertigo, cough, urticaria, pruritus and anaphylaxis. The sedating antihistamines are also used as mild sleeping aids and to alleviate tension and anxiety. Many antihistamines are also available in topical forms, as creams, nasal sprays and eye drops for local use in alleviating allergic symptoms. The nonsedating antihistamines are typically used in extended or long term treatment of allergic disorders, including allergic rhinitis (hay fever), sinusitis, atopic dermatitis, and chronic urticaria.
组胺是速发型超敏反应的重要介质，在局部起作用，可引起平滑肌收缩、血管扩张、血管通透性增加、水肿和炎症。组胺通过特定的细胞受体发挥作用，这些受体已被分为H1至H4四种类型。抗组胺药是一类能阻断组胺1型（H1）受体的药物。重要的是，抗组胺药并不阻断或减少组胺的释放，而是减轻其局部作用。专门阻断其他H2受体的药物通常被称为H2受体阻滞剂，而非抗组胺药。H1受体分布广泛，在支气管、胃肠道、子宫和大血管的平滑肌上尤其常见。H1受体也存在于中枢神经系统中。抗组胺药被广泛用于治疗过敏性疾病的症状，包括瘙痒、鼻塞、流涕、流泪、荨麻疹、头晕、恶心和咳嗽。它们单独使用或与其他药物联合使用最常见的用途是治疗上呼吸道疾病的症状，如普通感冒。抗组胺药对中枢神经系统的作用包括镇静以及减轻焦虑、紧张和不自主运动。根据其对中枢神经系统的作用，抗组胺药通常分为具有镇静作用的（第一代）和无镇静作用的（第二代），无镇静作用的药物较不易穿过血脑屏障。此外，一些抗组胺药还具有额外的抗胆碱能、抗毒蕈碱或其他作用。抗组胺药是医学上最常用的药物之一，大多数有多种剂型，可通过处方获得，也有非处方药，可单独使用，或与镇痛药或拟交感神经药联合使用。常见用途包括短期治疗普通感冒、季节性过敏性鼻炎（花粉症）、晕动病、恶心、眩晕、咳嗽、荨麻疹、瘙痒和过敏反应的症状。具有镇静作用的抗组胺药还用作轻度安眠药，并用于缓解紧张和焦虑。许多抗组胺药也有局部剂型，如乳膏、鼻喷雾剂和眼药水，用于局部缓解过敏症状。无镇静作用的抗组胺药通常用于过敏性疾病的长期或延长治疗，包括过敏性鼻炎（花粉症）、鼻窦炎、特应性皮炎和慢性荨麻疹。
