Antihistamines for Allergies

Products

Antihistamines are often taken in the form of tablets. In addition, drops, solutions, lozenges, capsules, gels, creams, eye drops, nasal sprays, and injectable solutions are also available, among others. The first active ingredient from this group was phenbenzamine (Antergan), developed in France in the 1940s. It is no longer commercially available today.

Structure and properties

The traditional antihistamines are alkylamines, ethylenediamines, phenothiazines, and piperazines. Today, representatives that do not belong to these groups are also on the market. Antihistamines have played an important role as precursors to neuroleptics and antidepressants.

Effects

Antihistamines (ATC R06) have antihistamine, antiallergic, antipruritic, and anti-inflammatory properties. They are partially adjunctive:

Antihistamines are inverse agonists at the histamine H1 receptor, meaning they stabilize the receptor in its inactive conformation. Thus, they cancel the effects of histamine and relieve allergic symptoms. Thus, antihistamines are not histamine receptor antagonists.

Indications

Indications for use include:

  • Allergic diseases
  • Allergic rhinitis, hay fever
  • Allergic conjunctivitis
  • Hives
  • Histamine intolerance
  • Itching
  • Insect bites, mosquito bites
  • Vomiting, pregnancy vomiting
  • Common cold
  • Cough
  • Motion sickness
  • Dizziness
  • Sleep disorders

Active ingredients 1st generation

First-generation agents are generally not specific for the H1 receptor, are anticholinergic, cross the blood–brain barrier, and enter the brain. There, they trigger central disturbances such as fatigue, drowsiness, and dizziness because they interact with central receptors. They have a shorter duration of action than 2nd-generation antihistamines and therefore must be administered more frequently. 1st-generation antihistamines are controversial and should be used cautiously and not at all for some indications:

  • Bamipin (Soventol, D).
  • Chlorphenamine (eg, Arbid drops).
  • Chlorphenoxamine (Systral, D)
  • Clemastine (Tavegyl)
  • Cyproheptadine (USA)
  • Dimenhydrinate (Trawell, others).
  • Dimetindene maleate drops (Feniallerg), dimetindene maleate gel (Fenistil).
  • Diphenhydramine (Benocten, Benylin, others).
  • Doxylamine (Sanalepsi)
  • Hydroxyzine (Atarax)
  • Ketotifen (Zaditen)
  • Meclozine (Itinerol B6)
  • Mepyramine (Stilex)
  • Oxomemazine (Toplexil)
  • Pheniramine (NeoCitran)
  • Tripelennamine (vetibenzamine, for animals).

No longer available in many countries:

  • Buclizine (Longifene)
  • Carbinoxamine (Rhinotussal)
  • Cyclizine (Marzine)
  • Dexbromopheniramine (Disofrol)
  • Dexchloropheniramine (Polaramine)
  • Diphenylpyralin (Arbid drops, old formulation).
  • Promethazine (Rhinathiol Promethazine, Broncatar).
  • Phenyltoloxamine (Codipront)

Active ingredients 2nd generation

Second-generation agents are generally specific for the H1 receptor and less depressant. They are therefore also called “non-sedating antihistamines”, but they can less often cause drowsiness. They do not cross the blood–brain barrier, are specific for the H1 receptor, and are not anticholinergic. They also have a longer duration of action of 12 to 24 hours and therefore need to be administered only once daily.

The following agents are not or no longer on the market in many countries:

  • Acrivastine (Semprex, out of commerce).
  • Ebastine (Ebastel, D)
  • Mizolastine (Mizollen, out of trade)
  • Rupatadine
  • Terfenadine (Teldane, out of trade)

External antihistamines

Eye drops:

Nasal sprays:

Dermatics: