A client who suffers from severe persistent allergic asthma is prescribed omalizumab (Xolair). Which statement below correctly describes the mechanism of action associated with omalizumab (Xolair)?

A. Stimulates effects of histamine by occupying all H receptor sites: This statement inaccurately describes the action of diphenhydramine. Instead of stimulating histamine effects, diphenhydramine actually blocks them, particularly at H1 receptors, which are involved in allergic responses.

B. Blocks effects of histamine by competing and occupying H1 receptor sites: This accurately describes the mechanism of action of diphenhydramine. As an antihistamine, it competes with histamine for binding to H1 receptor sites, effectively reducing symptoms of allergies, such as sneezing, itching, and nasal congestion.

C. Blocks effects of histamine by competing and occupying H2 receptor sites: This option is incorrect because H2 receptor antagonists are used primarily to reduce gastric acid secretion, not to treat allergic reactions. Diphenhydramine specifically targets H1 receptors, not H2 receptors.

D. Stimulates effects of histamine by increasing the amount of H2 receptor sites: This statement is also incorrect. Diphenhydramine does not stimulate histamine activity or increase receptor sites. Instead, it functions to inhibit the action of histamine at H1 receptors, which is fundamental in alleviating allergy symptoms.

A. Stimulate alpha-adrenergic receptors, thus producing vascular constriction of capillaries in nasal mucosa: This describes the action of decongestants, not guaifenesin. Guaifenesin does not work by constricting blood vessels; rather, its primary function is to help manage mucus production.

B. Compete with histamine for receptor sites, thus preventing a histamine response and overall congestion: This mechanism is associated with antihistamines, which are used to relieve symptoms of allergic reactions, not with guaifenesin. Guaifenesin does not block histamine but focuses on mucus management.

C. Treat allergic rhinitis and prevent motion sickness: While these are common uses for antihistamines, they do not apply to guaifenesin. Guaifenesin is primarily an expectorant and is not indicated for treating allergic rhinitis or motion sickness.

D. Loosen bronchial secretion to assist in elimination: Guaifenesin acts as an expectorant, promoting the clearance of mucus from the airways by loosening bronchial secretions. This facilitates easier expectoration of mucus, helping to relieve chest congestion associated with upper respiratory infections.