Antihistamine
The vast majority of marketed H-antihistamines are receptor antagonists and only a minority of marketed compounds are inverse agonists at the receptor. Clinically, H-antihistamines are used to treat allergic reactions and mast cell-related disorders. Sedation is a common side effect of H-antihistamines that readily cross the blood–brain barrier; some of these drugs, such as diphenhydramine and doxylamine, are therefore used to treat insomnia. H-antihistamines can also reduce inflammation, since the expression of NF-κB, the transcription factor the regulates inflammatory processes, is promoted by both the receptor's constitutive activity and agonist (i.e., histamine) binding at the H receptor.
Tubocurarine chloride
Tubocurarine has a time of onset of around 5 minutes which is relatively slow among neuromuscular-blocking drugs, and has a duration of action of 60 to 120 minutes. It also causes histamine release, now a recognized hallmark of the tetrahydroisioquinolinium class of neuromuscular blocking agents. Histamine release is associated with bronchospasms, hypotension, salivary secretions, making it dangerous for asthmatics, children, and those who are pregnant or lactating. However, the main disadvantage in the use of tubocurarine is its significant ganglion-blocking effect, that manifests as hypotension, in many patients; this constitutes a relative contraindication to its use in patients with myocardial ischaemia.