Antihistamines

 

There is a very nice review about histamine and antihistamines in the most recent Journal of Allergy and Clinical Immunology by Drs. Simons and Simons. The review was to commemorate 100 years since the discovery of histamine as a mediator and 70 years since antihistamines have been available for clinical use.

H1 antihistamines are the largest class of medication available with >45 available. These agents act against histamine’s effect on allergic inflammation. There are two general classes of these agents- first generation and second generation. Better put, the old ones that can get into the brain and cause sedation and the newer ones that tend to not to be sedating.

The older or first generation of antihistamines became available at a time when regulations were different and because of this, there is a lack of information about how these agents are handled in a variety of special populations; children and infants specifically. The new generation of these agents has undergone rigorous evaluations. These studies have shown that tolerance does not occur with the regular use of these agents. In other words, you do not become immune to these agents.

 Antihistamines work for and are indicated for the following conditions (where they are the medications of choice);

  •  Allergic rhinitis (nasal allergy)
  • Allergic conjunctivitis (eye allergy)
  • Acute urticaria (hives)
  • Other- mastocytosis, mosquito bite reactions, immunotherapy reactions

In these three conditions, there have been hundreds of well-designed studies that support their effects. The evidence is there.

A couple of points were made;

  •  Antihistamines do not work in nasal symptoms not due to allergy
  • Some will work within 15 minutes others may begin to show an effect in 2.5 hours
  • Topical nasal antihistamines may work as good as or better than oral antihistamines for congestion
  • Hives that last longer than 6 weeks, chronic hives, may require doses 4-fold higher
  • Current guidance for chronic hives has the H2-class as the antihistamine of choice at high dose

 Conditions for which an antihistamine is not the medication of first choice;

  •  Atopic dermatitis
  • Asthma
  • Anaphylaxis
  • Nonallergic angioedema
  • Other disorders

The points made regarding these conditions were;

  •  There have been no high-quality studies to confirm their efficacy in atopic dermatitis
  • The use of antihistamines in atopic dermatitis is still sometimes used for sedation effects (which would be the first generation antihistamines).
  • A review of 2070 studies on the use of antihistamines with anaphylaxis could not identify a good study that provided solid evidence for the use of these agents in anaphylaxis. They decrease itch and hives. They do not prevent or relieve airway/throat swelling.
  • The efficacy of antihistamines to treat colds, ear infections, sinus infections, nasal polyps, nonspecific cough, nonspecific itching has not been confirmed in well done studies.

 Conditions for which the first generation antihistamines have been used;

The first generation antihistamines have been used in a variety of conditions, however the evidence to support their use is considered weak. Most of these conditions involve the central nervous system;

  •  Insomnia
  •  Conscious sedation
  •  Perioperative sedation
  •  Analgesia
  •  Anxiety
  •  Serotonin syndrome
  •  Akathisia
  •  Migraine
  •  Motion sickness
  •  Vertigo

 Reviewer’s note-

Antihistamines are one of the most frequently used agents and have been used for a variety of conditions. They work for some things and not for others. I have seen multiple antihistamines used in the same child and choices made for perhaps the wrong reasons. Also of note is to keep in mind that when a study is done, there are responders and non-responders. Sometimes there are not enough responders to show a significant difference. The conclusion from such a study could be that the agent does not work and would not be recommended overall. A question to ask is whether it had an effect in anyone or was it a total non-response?

The take home messages for me- when they stop working think of some non-allergic issue, tolerance does not develop. If you use these for atopic dermatitis, you are looking for sedation. It would make more sense to go with the first generation agents in this condition. In conditions that do not respond, the dose may need to be increased as opposed to adding a second agent. Don’t ask more of the antihistamines than they can deliver.

 

FEL (December 24, 2011)

 

December 24, 2011 · fleickly · One Comment
Tags: ,  · Posted in: Antihistamines, Medications used to treat allergy

One Response

  1. Allergist Palo Alto - February 8, 2012

    Hi There Pediatricallergyindy,
    I was wondering on a similar note,, Long ago, pioneering self-help author Napoleon Hill was struggling to name his forthcoming book. Neither he nor the publisher were satisfied with their tentative title, The Thirteen Steps to Riches. Although Hill had thought up more than 500 other titles, they simply didn’t have a title worthy of the book.
    Wishes