Antihistamines that target the histamine H receptors in the upper gastrointestinal tract, primarily in the stomach.
Histamine receptors exhibit constitutive activity, so antihistamines can function as either a neutral receptor antagonist or an inverse agonist at histamine receptors.
Some second-generation antihistamines, notably cetirizine, can interact with CNS psychoactive drugs such as bupropion and benzodiazepines.-antihistamines are among first-line therapy to treat gastrointestinal conditions including peptic ulcers and gastroesophageal reflux disease. Most side effects are due to cross-reactivity with unintended receptors.
Cimetidine, for example, is notorious for antagonizing androgenic testosterone and DHT receptors at high doses.
This sedating activity is sometimes used in managing conditions such as eczema where sleep maybe disturbed due to pruritus.
As an alternative to taking an antihistamine, people who suffer from allergies can instead avoid the substance which irritates them.
However, this is not always possible as some substances, such as pollen, are carried in the air, thus making allergic reactions caused by them generally unavoidable.
Although people typically use the word “antihistamine” to describe drugs for treating allergies, doctors and scientists use the term to describe a class of drug that opposes the activity of histamine receptors in the body.-receptor are used to treat allergic reactions in the nose (e.g., itching, runny nose, and sneezing) as well as for insomnia.
They are sometimes also used to treat motion sickness or vertigo caused by problems with the inner ear.
The newer antihistamines are available only by prescription.