Antihistamines

Antihistamines Nursing Pharmacology Study Guide

Antihistamines NCLEX Nursing Pharmacology Review

Nursing Pharmacology Guide on Antihistamines

Antihistamines are a class of drugs that are used to treat nasal allergies by means of reducing rhinorrhea and sneezing. In particular, antihistamines are commonly given to patients with allergic rhinitis or hay fever.

It can also be administered for patient with vasomotor rhinitis, urticaria, and drug allergies. It is important to note that antihistamines do not usually resolve nasal congestion. 

Many antihistamines produce sedation as a side effect, but newer antihistamines can have a less potent sedative effect than older ones. They are available in various forms, and can be administered via oral, intravenous, ocular, rectal, and topical routes.

Some antihistamines can be purchased over-the-counter, while others require a prescription.

Indications for Antihistamines

Antihistamines can be administered to prevent or treat:

  • Allergic rhinitis or hay fever
  • Allergic conjunctivitis
  • Food allergies
  • Hives and skin rashes
  • Colds
  • Insect bites and stings
  • Anaphylaxis or severe allergic reaction
  • Infusion-related reactions associated with systemic anti-cancer therapy (SACT)
  • Gastro-intestinal disorders, particularly those that are acid-related such as gastritis and heartburn
  • Depression, insomnia, and anxiety
  • Zollinger-Elison syndrome
  • Headaches and vertigo
  • Anorexia
  • Parkinson’s disease – to aid in controlling tremors and stiffness

Actions of Antihistamines

Histamine is an important chemical produced by the immune system in response to allergens such as pollen, dust, food, pet dander, and chemicals. It helps start the process of removing these allergens that the body considers “foreign”.

But when there is an overreaction of histamines, allergic reactions occur, which lead to swelling and dilation of vessels. These manifest as sneezing, coughing, and watery eyes. Antihistamines work by blocking the action of histamine. There are two major subtypes of antihistamines: H-1 receptor antagonists and H-2 receptor antagonists.

  1. H-1 receptor antagonists. These antihistamines are used to treat allergic reactions, nausea and vomiting, vertigo, and motion sickness. H-1 receptor antagonists are further divided into two groups:
  2. First-generation antihistamines – act on the histamine receptor in the brain and spinal cord; able to cross the blood-brain barrier which make them potent sedatives; approved by the U.S. Food and Drug Administration (FDA) in the 1930s
  3. Second-generation antihistamines – work similar to the first-generation antihistamines but do not cross the blood-brain barrier; do not cause drowsiness and are therefore considered safer than first-generation antihistamines; approved by FDA in the 1980s
  4. H-2 receptor antagonists – these antihistamines block the H-2 receptors which are abundant in the gastrointestinal tract. They are used in the management of various gastrointestinal problems, such as acid reflux disease, gastritis, peptic ulcers, nausea and vomiting, and motion sickness.

Side Effects and Adverse Effects of Antihistamines

The common side effects of first-generation H-1 receptor blockers are:

  • Drowsiness
  • Dizziness
  • Dry mouth or eyes
  • Low blood pressure
  • Blurry or double vision
  • Increased heart rate
  • Constipation
  • Dysuria

The common side effects of second-generation H-1 receptor blockers are:

  • Headache
  • Cough
  • Sore throat
  • Tiredness
  • Nausea and vomiting
  • Abdominal discomfort or pain

The common side effects of first-generation H-2 receptor blockers are:

  • Drowsiness
  • Headache
  • Dizziness
  • Breast swelling and tenderness
  • Confusion in elderly patients
  • Joint or muscle pain
  • Dry mouth or eyes

Antihistamine overdose or antihistamine poisoning may happen if a person takes too much of the drug. Adverse reactions associated with antihistamines overdose may exhibit the following symptoms:

  • Increased drowsiness
  • Nausea and vomiting
  • Blurry vision
  • Rapid heart rate
  • Mental disturbances such as confusion
  • Loss of balance

Contraindications and Cautions against Antihistamines

There are different considerations and cautions related to the intake of antihistamines. They are commonly discussed by the prescriber before the medication is prescribed.

For first-generation antihistamines:

For second-generation antihistamines:

  • Kidney or renal disease – hepatic or liver impairment may cause an alteration in the uptake and excretion of antihistamines
  • Heart disease – a patient with history of arrhythmias or prolonged QT intervals can be prescribed with appropriate antihistamines but with extreme caution to prevent fatal cardiac arrhythmias

Patients on antihistamines should avoid operating heavy machinery and driving due to the drugs’ sedative property. Pregnant women should be advised to treat allergic rhinitis with non-drug interventions, such as using saline nasal sprays, nasal strips, and exercise.

If required, second generation antihistamines with an FDA category B are the preferred choice for pregnant women due to their generally better side effect profile as compared to first generation antihistamines.

Drug Interactions with Antihistamines

Due to the sedating effect of antihistamines, a patient should discuss with his/her healthcare provider about taking antihistamines with other medications, such as sleeping pills, antipsychotics, muscle relaxants, prescription narcotics, monoamine oxidase inhibitors (MAOI), and seizure medications.

Antihistamines should not be taken within 2 weeks of taking a MAOI. Patients on antihistamines should stop alcohol intake as well.

Nursing Care Plan for Patients on Antihistamines

Possible Nursing Diagnoses:

Disturbed Sleep Pattern (Drowsiness or Excessive Sleepiness) related to the sedative property of antihistamines

Risk for Injury Acute pain related to GI, CNS or skin effects of the drug

Disturbed sensory perception (Kinesthetic) related to CNS effects

Fatigue related to disturbed sleep pattern

Deficient Knowledge related to drug action and side effects

Nursing Assessment

InterventionsRationales
Check the patient’s diagnosis and how it relates to the administration of antihistamines. Assess the patient for signs and symptoms of allergic rhinitis or anaphylaxis. Check the patient’s allergy status.To confirm the indication for administering antihistamines.
Conduct a review of current medications and history of alcohol intake.Alcohol and some medications interact with antihistamines. Assess for the current use of sleeping pills, antipsychotics, muscle relaxants, prescription narcotics, monoamine oxidase inhibitors (MAOI), and seizure medications.
Assess if the patient is pregnant.      Second generation antihistamines with an FDA category B are the preferred choice for pregnant women due to their generally better side effect profile as compared to first generation antihistamines.
Check for the status of peripheral veins prior to cannulation and administration of intravenous antihistamines. If administering oral antihistamines, assess the patient’s mucous membranes and his/her ability to swallow.To check for any potential problems with administration, hydration, and absorption.
To ensure that the right form of antihistamines is given through the right route.
Check the patient’s medical history for the following: For first-generation antihistamines: GlaucomaBenign prostatic hyperplasia (BPH) that causes trouble urinatingRespiratory disorders such as asthma, emphysema, or chronic bronchitisThyroid diseaseHeart diseaseHypertension or High blood pressure For second-generation antihistamines: Kidney diseaseHeart disease  Antihistamines should be prescribed with extreme caution in patients with the mentioned diseases. Patients with hepatic or liver impairment may experience alteration in the uptake and excretion of antihistamines. On the other hand, a patient with history of arrhythmias or prolonged QT intervals can be prescribed with appropriate antihistamines but with extreme caution to prevent fatal cardiac arrhythmias.  

Nursing Planning and Intervention

InterventionsRationales
Administer oral antihistamines with food or a glass of water or milk. It is ideal to give it at the same time of the day.To ensure optimal absorption and therapeutic action by antihistamines. Antihistamines may cause gastrointestinal discomfort. Taking it with food or a glass of milk may help reduce the stomach irritation.
Educate the patient about the action, indication, common side effects, and adverse reactions to note when taking antihistamines. Instruct the patient on how to self-administer oral antihistamines.To inform the patient on the basics of antihistamines, as well as to empower him/her to safely self-administer the medication.
Advise the patient to avoid operating heavy machinery and driving due to the sedative property of antihistamines.Patients on antihistamines should avoid operating heavy machinery and driving due to the drugs’ sedative property. 
Educate the patient that he/she can have sugarless candies or lozenges for dry mouth. Encourage to increase oral fluid intake. Advise patient on proper skincare.Antihistamines may cause dryness of the mouth. 
Encourage the patient to avoid alcohol intake, or at least limit alcohol consumption to 1 to 2 units per day while taking antihistamines.Alcohol may increase the risk of disturbed sleep pattern while taking antihistamines. 
Inform the pregnant patient to try using non-medication interventions first for allergic rhinitis.Antihistamines have an FDA category of either B or C. 

4.  Nursing Evaluation

InterventionsRationales
Ask the patient to repeat the information about antihistamines.To evaluate the effectiveness of health teaching on antihistamines.
Monitor the mental status of the patient.To ensure that the antihistamines did not cause any confusion, excessive drowsiness, or other mental disturbances to the patient.
Monitor the patient’s response to antihistamines in terms of side effects or adverse effects, particularly drowsiness, dysuria, and blurry vision.To check if the antihistamines are effective, the dose needs to be adjusted, or the drug should be stopped and changed to an alternative treatment.
Advise the pregnant patient to monitor for any increased drowsiness or confusion after commencing antihistamine therapy.Excessive drowsiness and mental disturbances are adverse effects of taking antihistamines. The drug must be stopped to ensure the safety of the mother and fetus.

Nursing References

Ackley, B. J., Ladwig, G. B., Makic, M. B., Martinez-Kratz, M. R., & Zanotti, M. (2020). Nursing diagnoses handbook: An evidence-based guide to planning care. St. Louis, MO: Elsevier.  Buy on Amazon

Gulanick, M., & Myers, J. L. (2017). Nursing care plans: Diagnoses, interventions, & outcomes. St. Louis, MO: Elsevier. Buy on Amazon

Ignatavicius, D. D., Workman, M. L., Rebar, C. R., & Heimgartner, N. M. (2018). Medical-surgical nursing: Concepts for interprofessional collaborative care. St. Louis, MO: Elsevier.  Buy on Amazon

Silvestri, L. A. (2020). Saunders comprehensive review for the NCLEX-RN examination. St. Louis, MO: Elsevier.  Buy on Amazon

Disclaimer:

Please follow your facilities guidelines, policies, and procedures.

The medical information on this site is provided as an information resource only and is not to be used or relied on for any diagnostic or treatment purposes.

This information is intended to be nursing education and should not be used as a substitute for professional diagnosis and treatment.

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