Histamine is released in many allergic states, but it is not the sole cause of symptoms, other chemical mediators, e.g., leukotrienes and prostaglandins, also being involved. Hence the usefulness of Hj-receptor antihistamines in allergic states is variable, depending on the extent to which histamine, rather than other mediators, is the cause of the clinical manifestations.
Hay fever. If symptoms are limited to rhinitis, a glucocorticoid (beclomethasone, betamethasone, budesonide, flunisolide or triamcinolone), ipratropium or sodium cromoglicate applied topically as a spray or insufflation is often all that is required. Ocular symptoms alone respond well to sodium cromoglicate drops. When both nasal and ocular symptoms occur, or there is itching of the palate and ears as well, a systemic nonsedative Hj-antihistamine is indicated. Sympathomimetic vasoconstrictors, e.g. ephedrine, are immediately effective if applied topically, but rebound swelling of the nasal mucous membrane occurs when medication is stopped. Rarely, a systemic glucocorticoid, e.g. prednisolone, is justified for a severely affected patient to provide relief for a short period, e.g. during academic examinations.7
Hyposensitisation, by subcutaneous injection of graded and increasing amounts of grass and tree pollen extracts, is an option for seasonal allergic hay fever due to pollens (which has not responded to anti-allergy drugs), and of bee and wasp allergen extracts for people who exhibit allergy to these venoms (exposure to which can be life threatening). If it is undertaken facilities for immediate cardiopulmonary resuscitation must be available due to the risk of anaphylaxis.
Urticaria, see page 143.
Anaphylactic shock, see page 143.
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