Antihistaminic action

Despite their common ability to enhance serotonergic function in vivo, the SSRIs differ both in terms of their pharmacological profiles and their pharmacokinetics. Thus in addition to their direct inhibitory action on the serotonin transporter, they also affect other neurotransmitter systems which may have some clinical relevance. Citalopram has a modest antihistamine action which might account for its slightly sedative action. Sertraline has a... 

Mechanism of Action A phenothiazine that blocks dopamine neurotransmission at postsynaptic dopamine receptor sites. Possesses strong anticholinergic, sedative, and antiemetic effects moderate extrapyramidal effects and slight antihistamine action. Therapeutic Effect Relieves nausea and vomiting improves psychotic conditions controls intractable hiccups and porphyria. 

A pharmacological development program embarked on by the drug company Rhone Poulenc in Paris to screen for medicaments having an antihistamine action. 

Antihistaminic action The antihistaminics blocks histamine effects at a variety of sites. They inhibit most responses of smooth muscles to hista-... 

NA, not avaiiabie IV, intravenous IM, intramuscuiar. antimuscarinic and moderate antiserotonin actions. Chiorphenamine causes iess sedation than some other antihistamines. Transient CNS stimuiant effects may be seen when injected intravenously. Chiorphenamine is a racemic mixture, with the antihistamine action residing mainly in the (+) laevo isomer (dexchiorphenamine). This isomer is aiso commerciaiiy avaiiabie. 

There are also numerous antidepressants that have sedative-hypnotic properties (Table 8—4). Some of these antidepressants are sedating owing to anticholinergic-antihistaminic actions. Not surprisingly, the tricyclic antidepressants (TCAs) can therefore be useful hypnotics to induce sleep in some patients. Thus, skillful use of a TCA in a depressed patient with insomnia can turn the liability of unwanted sedation into the asset of relief of insomnia if the TCA is given at bedtime. This property, as discussed in Chapter 6, has nothing to do, however, with the reason that TCAs are antidepressants (shown in Figs. 6—15 and 6—16). 

FIGURE 11—7. This figure represents an icon of a conventional antipsychotic drug. Such drugs generally have at least four actions blockade of dopamine 2 receptors (D2) blockade of muscarinic-cholinergic receptors (Ml) blockade of alpha 1 adrenergic receptors (alpha 1) and blockade of histamine receptors (antihistaminic actions [HI ). 

Golightly LK, Greos LS. Second-generation antihistamines actions and efficacy in the management of allergic disorders. Drugs. 2005 65 341-384. 

Antihistaminic actions may cause sedation, weight gain... 

Agents with antihistamine actions (e.g., diphenhydramine, tricyciic antidepressants)... 

Clinical practice suggests that at low doses it may be a sedative hypnotic, possibly due to potent HI antihistamine actions, but this is an expensive use for which there are many other options... 

Pizotifen and cyproheptadinehlockseTotomn (5-HT) receptors as weU as having some Hj-antihistamine action they can be effective. 

Interactions may also result from the concurrent use of two or more products available without a prescription. In some situations, two non-prescription products promoted for different purposes contain the same active ingredient(s), which increases the risk of an excessive response to these agents. Diphenhydramine is included in many products for its antihistamine action but also is included for its sedative effect in many non-prescription sleep aids. Patients are often unaware that the products they purchase for different conditions may contain the same active ingredients. This puts users at increased risk for interaction... 

Cyproheptadine is an antihistaminic and antis-erotonergic agent that also has anticholinergic and sedative effects. It is used for its antihistaminic actions in humans. It has been used with limited success in the treatment of pars intermedia dysfunction in horses. 

Some horses exhibiting signs of photic headshaking respond favorably to treatment with the antihistamine drug cyproheptadine (Wilkins 1997). In addition to antihistaminic action, cyproheptadine has anticholinergic action and is a 5-hydroxytryptamine (serotonin) antagonist, altering proopiomelanocortin peptide metabolism... 

Trimeprazine Tartrate. USP. Trimcprazinc tartrate. I )IO- 3-(dimcthylamino)-2-mcthylpropyl phenothia/inc tartrate (Tcmaril), wcurs as a white to off-white crystalline powder that is freely soluble in water and soluble in alcohol. Its antihistaminic action is repotted to be from 1.5 to 5 times dial of promethazine. Clinical. studies have shown it has a pronounced antipruritic action. This action may be unrelated 10 iLs histaminc-antagoni/.ing propcrtic.s. 

Sedation is related to the antihistamine action and the a-adrenergic blocking properties (phenothiazines are therefore very sedative). 

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