Antihistamine Usage

• It is important to understand the important uses of antihistamines and how to use those properly.
• There are various drug interactions and adverse reactions related to antihistamines that must be understood.
• The nurse has an important role involving the nursing process and patient education with antihistamine usage.

Antihistamines or H1 receptor antagonists work by blocking the action of histamine that occurs in a type I hypersensitivity reaction or an allergic reaction.  They are available as prescription drugs or over the counter and can be given alone or in combination with other medications.

Antihistamine competes with the histamine binding at the H1 receptor site; however, it cannot displace the histamine already bound to the receptors.

Antihistamines cannot reverse the ongoing allergic reaction because they cannot displace the already-bound histamine to the H1 receptors, but they can prevent further allergic reactions by competing with histamine binding at the H1 receptor site.

Uses of Antihistamines

Antihistamines are used to relieve signs and symptoms of type 1 hypersensitivity reactions such as:

• Allergic rhinitis that causes runny nose and itchy eyes caused by a local sensitivity reaction
• Vasomotor rhinitis (that is not caused by allergy or infection)
• Allergic conjunctivitis or inflammation of the eye membranes
• Urticaria or hives
• Angioedema – submucosal swelling in the hands, face, and feet

Antihistamines have other therapeutic uses such as:

• Antiemetic to control nausea and vomiting
• Serve as an adjunct when symptoms are under control
• Diphenhydramine can be used to help treat Parkinson’s disease and drug-induced extrapyramidal reactions that involve abnormal involuntary movements.

Drug Interactions and Adverse Reactions

Drug Interactions

Drug interactions with antihistamines can be serious and may include the following:

• Antihistamines can interact with epinephrine, blocking or reversing its vasopressor effects, producing vasodilation, dangerously low blood pressure, and increased heart rate.
• Antihistamines can mask the symptoms of ototoxicity that occur with aminoglycosides or large doses of salicylate ingestion; therefore, one should avoid their concomitant use.
• Antihistamines with CNS depressants such as benzodiazepines or alcohol can cause increased sedation and/or respiratory depressive effects.
• Loratadine, when given with macrolide antibiotics (such as erythromycin, fluconazole, ketoconazole, itraconazole, miconazole, cimetidine, ciprofloxacin, and clarithromycin) can cause serious cardiac effects; therefore, one should avoid their concomitant use.

Adverse Reactions

The most common side effect of antihistamines is CNS depression that causes sedation.  They can also cause the following:

• dizziness
• fatigue
• disturbed coordination
• muscle weakness
• epigastric distress
• loss of appetite
• nausea and vomiting
• constipation
• diarrhea
• dryness of the mouth, nose, and throat
• hypotension
• hypertension
• rapid heart rate
• arrhythmias

Nursing Process and Patient Education

Nursing Process

The following nursing processes are appropriate for patients taking antihistamines therapy.

Assessment

• Obtain the patient’s history before starting the antihistamine therapy and assess his/her health status periodically.
• Check the patient for any drug interactions or adverse drug reactions.
• With long-term therapy, monitor the patient’s blood counts and check for blood dyscrasias.
• Check the patient and family member’s knowledge of the medication therapy.

Key Nursing Diagnosis

• Ineffective health management due to a possible underlying condition
• Risk for injury related to CNS side effects due to the medication therapy
• Knowledge Deficit related to medication therapy

Planning Outcome Goals

• The patient’s underlying health condition will improve.
• The patient will have minimal risk of injury due to any adverse CNS effects.
• The patient and family will demonstrate and verbalize their understanding of medication therapy.

Evaluation

• The patient’s underlying health condition improves.
• The patient sustains no injuries from medication therapy.
• The patient and his/her family demonstrate an understanding of drug therapy.

Patient Education

With antihistamine therapy, the following points need to be discussed with the patient and their caregiver:

• Give the antihistamine with food to prevent stomach upset.
• Avoid consuming alcohol, nicotine, or caffeine.
• Use warm-water rinses, artificial saliva, ice chips, sugarless gum, or candy to relive dry mouth.
• If one takes the medication to prevent motion sickness, take it 30 minutes before traveling.
• Avoid hazardous activities such as operating machinery or driving until one is aware of any possible CNS effects that may take place. Avoid taking them if feeling sleepy.
• Seek medical approval first if one has a history of using alcohol, tranquilizers, sedatives, pain relievers, or sleep medications.
• Before having a diagnostic skin test, stop antihistamines 4 days before to preserve the accuracy of the test results.
• If antihistamines do not provide relief from allergy symptoms, intolerance may be the issue. Inform one’s healthcare provider in case a medication change is needed.
• Be cautious with antihistamines as they may cause photosensitivity. Use sunscreen and wear protective clothing.
• Avoid using other products containing diphenhydramine, including over-the-counter and topical forms, while breastfeeding because of the risk of adverse reactions.
• If an antihistamine is being used for insomnia, take it 20 minutes before going to bed.

The Bottom Line

Antihistamines remain essential agents in relieving allergy symptoms, but it is important for the patient to understand the importance of attending follow-up visits in order for his/her health to be monitored effectively.  Tolerance can occur if one takes antihistamines for an extended period of time and tolerance can lead to ineffectiveness. 

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