Antihistamines pharmacologic effects

Zipeprol [34758-83-3] (58) is another European antitussive with a wide range of pharmacological effects, including antispasmodic, antihistaminic, and local anesthetic activities (85,86). It has been reported that zipeprol has been abused in Italy because high doses cause hallucinations (87). Spontaneous withdrawal symptoms similar to those of opiates have been observed withdrawal symptoms can also be precipitated by naloxone. Zipeprol can be... 

Cimetidine is a representative of first-generation antihistamine drugs that block H2 receptors. The main pharmacological effect of cimetidine is the suppression of gastric juice secretion associated with H2 receptors of the stomach walls. It suppresses both basal and stimulated hyckochloric acid produced by food as well as histamine and gastrine, which simultaneously lower pepsin activity. 

In pharmacodynamic interactions, the pharmacological effect of a drug is changed by the action of a second drug at a common receptor or bioactive site. For example, low-potency antipsychotics and tertiary amine TCAs have anticholinergic, antihistaminic, a-adrenergic antagonist, and quinidine-Kke effects. Therefore, concurrent administration of chlorpromazine and imipramine results in additive sedation, constipation, postural hypotension, and depression of cardiac conduction. 

Estazolam potentiates the CNS depressant effects of phenothiazines, narcotics, antihistamines, MAOIs, barbiturates, alcohol, general anesthetics, and TCAs. Use with cimetidine, disulfiram, oral contraceptives, and isoniazid may diminish hepatic metabolism and result in increased plasma concentrations of estazolam and increased CNS depressant effects. Fleavy smoking (more than 20 cigarettes/day) accelerates estazolam s clearance. Theophylline antagonizes estazolam s pharmacological effects. 

The pharmacologic effect of Hi antihistamines is to prevent histamine-Hi receptor interaction. Additionally, other receptors may be affected (Figure 13-3), antiinflammatory effects may occur, and mast cell and basophil mediator release is prevented. An increased luiderstanding of the pharmacologic mechanism has resulted in Hi antihistamines being reclassified as inverse agonists. 

Some ADRs are caused by most or all medications in a class, while others are agent specific. Nausea, vomiting, and diarrhea have been observed with most antibiotics, yet only chloramphenicol and certain sulfonamide antibiotics have been consistently implicated as causes of aplastic anemia. Some pharmacological effects, such as sedation from an antihistamine, may be considered adverse effects when they are... 

Antihistamines. The pharmacologic effects of antihistamines are summarized as follows ... 

Pyrilamine competitively antagonizes histamine at the H,-receptor site but does not bind with histamine to inactivate it. Terfenadine and astemizole, the most specific Hj antagonists available, bind preferentially to peripheral rather than central Hj receptors. Antihistamines do not block histamine release, antibody production, or antigen-antibody interactions. They antagonize in varying degrees most of the pharmacological effects of histamine. 

Pharmacologic Therapy Topical emollients have been used as treatment for pruritus in patients with dry skin, but are often not effective in relieving pruritus associated with CKD. Antihistamines, such as hydroxyzine 25 to 50 mg or diphenhydramine 25 to 50 mg orally or intravenously, are used as... 

It was noted, however, that a subset of responses known to be triggered by histamine failed to be blocked by the classical antihistaminic drugs. This, as well as further sophisticated pharmacological work, led to the classification of histamine receptors as and Hg. To simplify grossly, the receptor controls the responses familiar to every hayfever sufferer these effects can be alleviated readily by classicial antihistamines. The latter interestingly bear little or no structural similarity to histamine... 

Utilizing the same aryl fluoride linker on conventional MeOPEG polymer, these authors also presented a microwave-accelerated liquid-phase synthesis of benzimidazoles (Scheme 7.70) [79]. This bicydic pharmacophore is an important and valuable structural element in medicinal chemistry, showing a broad spectrum of pharmacological activities, such as antihistaminic, antiparasitic, and antiviral effects. 

There are also known cases of drug enantiomers that possess completely different therapeutic properties. The (+)-2/ ,35 -stereoisomer of propoxyphene (dextropropoxyphene) is marketed as an analgesic agent, whereas its enantiomer ( )-(25, 3/ )-propoxyphene (levopropoxyphene) is available as an effective anti-tussive agent [3]. The enantiomers of some chiral drugs are known to possess essentially identical qualitative and quantitative pharmacological activities, for example, the antihistamine promethazine, which is marketed as a racemate [5]. 

Traditional or Hj antihistamine drugs block many effects caused by histamine however, it turns out that they are not able to withstand events mediated by H2 receptors, in particular excess gastric juice secretion. In 1977 an H2-receptor antagonist, cimetidine, was proposed, which revolutionized stomach ulcer treatment. Later on, ranitidine was proposed, followed by drugs with minor structural and pharmacological differences such as famotidine and nizatidine. 

In the treatment of children and adolescents with anxiety disorders clinicians have a wide variety of pharmacologic options beyond the antidepressants (Shader and Greenblatt, 1995 Lydiard et ah, 1996 Riddle et ah, 1999). The benzodiazepines (BZs), with their favorable safety profile and quick onset of action, are attractive alternatives for the treatment of acute anxiety. While the clinical effectiveness of buspirone has not been proven in children, buspirone is used alone or in combination with other drugs in the treatment of anxiety disorders. The antihistamines are often used to treat insomnia and may reduce acute mild agitation. Zolpidem (Ambien) is occasionally used for its sedative properties. This chapter reviews the structure, proposed mechanisms of action, pharmacodynamic principles, and pharmacokinetic principles of these drugs. 

After the discovery of drugs with antidepressant activity in the late 1950s, an intensive search was undertaken for pharmacological models that would provide an understanding of the therapeutic effects observed and at the same time assist in the development of other, still more effective and specific antidepressants. In pharmacological tests then available, the prototype imipramine showed sedative, antihistaminic and anticholinergic effects and thus did not differ fundamentally from other medicaments with no antidepressant activity, e.g. antihistamines. The following observations then led to a further step forward in the development of hypotheses ... 

Side effects are also based on different facet of action (or side effects unrelated to its pharmacological or therapeutic effect). All antihistaminics except few newer compounds e.g. astemizole, terfenadine etc. cause sedation which is unrelated to its therapeutic action i.e. antiallergic action. 

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