Second-Generation (Nonsedating) Antihistamines

More recent nonsedating antihistamines offer the advantage of fewer side effects over sedating antihistamines, as they are peripherally acting antihistamines. They are also currently available as over-the-counter medications. This has significantly increased their use. The therapeutic use for nonsedating antihistamines includes allergic rhinitis and treatment for chronic idiopathic urticaria, which is rash and hives that occur in relation to an unknown cause.

Prototype and Other Medications

The prototype nonsedating antihistamine for this group of medications is cetirizine. Other nonsedating antihistamine medications include loratadine, fexofenadine, and desloratadine.

Expected Pharmacologic Action

Nonsedating antihistamines antagonize histamine effects at H₁ receptor sites, without binding to or inactivating histamine. The anticholinergic effects for medications in this classification are minimal as compared to the sedating antihistamines. This action is what makes cetirizine so effective in the treatment of seasonal allergic rhinitis and idiopathic urticaria. Therapeutic effects are longer lasting than the first-generation antihistamines, so dosing is once daily.

Adverse Drug Reactions

Nonsedating antihistamines have significantly fewer side effects than sedating antihistamines and may be dose related. Some clients may still experience drowsiness, as well as fatigue, but dramatically less than the side effects caused by first-generation sedating antihistamines. Mild anticholinergic effects such as dry mouth, nose, and throat may also occur, but again, much less than what clients experience with first-generation sedating antihistamines.

Interventions

When caring for clients taking nonsedating antihistamines, especially with dosages higher than 10 mg per day, assess them during ambulation to determine their degree of drowsiness and fatigue. Then, ensure that they have water available if their mouth or throat becomes dry. Also, clients can suck on hard candy to relieve dryness. Encourage clients to maintain fluid intake of 1,500 to 2,000 mL per day to alleviate viscosity of secretions.

Administration

Nonsedating antihistamines can be given with or without food, as they do not usually cause stomach upset. However, do not give them with other over-the-counter antihistamines. Decrease the dose of nonsedating antihistamines in clients who have compromised liver or kidney function.

Client Instructions

Tell clients to take nonsedating antihistamines once daily at a time convenient for them. Until the client determines the amount of drowsiness, instruct them to avoid driving and activities that require mental alertness. Make sure clients take frequent sips of water and suck on hard candy for dry mouth and throat.

Contraindications and Precautions

Do not give nonsedating antihistamines to infants under 6 months of age or women who are breastfeeding. Also, do not give to those with allergies to H₁antihistamine receptors or hydroxyzine. Also, use them cautiously with clients who have impaired kidney or liver function because of the risk of a delay in metabolism and excretion.

Interactions

There are two interactions to note with antihistamines. Theophylline can reduce the clearance of nonsedating antihistamines from the body and lead to toxicity. Concurrent use with sedative/hypnotics, opioid analgesics, or alcohol can potentiate CNS depression.