Histamine 1 antagonists
Histamineantagonists bind to the receptor blocking the action of histamine. Earlierantagonists were rather non-selective leading to variable actions. Sedation wasa prominent adverse effect of these drugs. Nowadays H1 and H2 selectiveantagonists are available. From the graphic their action can be deduced.
It could be expected that H1 antagonists would lead to bronchodilation due toblockade of smooth muscle contractions. However in practice this activity isnot clinically significant. These drugs can be used for amelioration of allergic rhinitis,conjunctivitis and eczema, but not of asthma.
H1 antagonists can lead to smooth muscle relaxation.
Extra info: This is true since the H1 antagonists inhibit smooth muscle contraction.
H1 antagonists have an important role in the treatment of obstructive lung disease.
Extra info: Despite having a mechanism of action that would reduce muscle contraction, the clinical application of these agents has not been found to be useful.