Antihistamines diphenhydramine

Administer the antihistamine diphenhydramine (Benadryl, adults 25-50 mg children 1-2 mg/kg) usually given parenterally. Apply tourniquet proximal to site of antigen injection remove every 10-15 minutes. 

Desloratadine is a non-sedating antihistamine. Diphenhydramine, chlor-phenamine, promethazine and alimemazine are sedating antihistamines with diphenhydramine and promethazine being marketed in over-the-counter hypnotic preparations. 

The antihistamine diphenhydramine (Benadry/), because it has anticholinergic properties, is used for mild parkinsonism and with the elderly, who may not be able to tolerate the more potent anticholinergics, levodopa, or the dopamine agonists. 

Hamelin, B.A., Bouayad, A., Methot, J., Jobin, J., Desgagnes, P., Poirier, R, Allaire, J., Dumesnil, J., and Turgeon, J. (2000) Significant interaction between the nonprescription antihistamine diphenhydramine and the CYP2D6 substrate metoprolol in healthy men with high or low CYP2D6 activity. Clin Pharmacol Ther 67 466 77. 

Silicon Containing Derivatives of the Antihistamines Diphenhydramine and Fenpiprane... 

The antihistamine diphenhydramine 169a) exhibits strong histaminolytic effects on the isolated guinea pig ileum, whereas its sila-analogue 169b hydrolyses [Eq. (24)] so fast that characteristic effects could not be detected. This can be explained easily by the presence of the sensitive Si—H and Si—OC bond. 

Metoclopramide (Reglan, and others) is both a serotonin- and dopamine-receptor antagonist. Given alone, it is less effective than TV ondansetron. Given concurrently with dexamethasone and either the antianxiety agent lorazepam (Ativan, and others) or the antihistamine diphenhydramine (Benadryl, and others), it can control emesis due to high-dose cisplatin (120 mg/m2) in older adults. One study in older patients, however, found metoclopramide, dexamethasone, and diphenhydramine less effective than IV ondansetron combined with dexamethasone in patients taking > 50 mg/m2... 

Phenobarbital, meprobamate, and sedative-autonomic drugs are used occasionally as antianxiety agents. The antihistaminics (diphenhydramine, hydroxyzine, promethazine) continue to be used presurgically for their sedative and muscarinic receptor blocking actions. 

Two brief examples are presented to illustrate structure-activity problems for which this approach might be useful. The first example (Fig. 16) finds the similar structural features among five structurally diverse antihistamines (diphenhydramine, methapyrilene, cyproheptadine, dimethindene and promethazine). 

Fig. 16. Similar structural feature among five antihistamines (diphenhydramine, methapyrilene, cyproheptadine, dimethindene and promethazine)...

The effect of levocetirizine 5 mg/day on actual driving performance during normal traffic has been compared with the effect of the first-generation antihistamine diphenhydramine 50 mg/day in 48 healthy volunteers in a double-blind, placebo-controlled, randomized trial (73). Treatments were given on days 1, 2, 3, and 4, at 90 minutes before the start of a standardized driving test on days 1 and 4. In contrast to diphenhydramine, driving performance was not significantly affected by levocetirizine 5 mg/day. 

Antihistamines Diphenhydramine 25-50 mg q.i.d. Rarely provide significant Drowsiness... 

Orphenadrine is related to an antihistamine (diphenhydramine), and appears to have been developed in the hope of producing a greater effect in Parkinson s disease by combining both anticholinergic and antihistaminic effects in a single molecule. 

C It is recommended that all patients receiving paclitaxel receive pretreatment to reduce the risk and severity of hypersensitivity reactions. The preferred regimen includes a combination of a corticosteroid (such as dexamethasone), an antihistamine (diphenhydramine or equivalent), and an Hj antagonist (such as cimetidine or ranitidine). Omeprazole and other PPIs will not block Hj-receptor sites and do not provide protection against hypersensitivity reactions. 

Answer B. Docusate is a stool-softening laxative that facilitates mixing of oil and water via its surfactant properties. Drugs that have muscarinic blocking effects, like scopolamine and the antihistamines diphenhydramine and promethazine, tend to cause constipation by decreasing GI motility. Loperamide is an opioid derivative, with no analgesic activity, used in the treatment of diarrheal states. 

In vitro studies on the isolated guinea-pig ileum have shown that the replacement of the central carbon atom in the antihistaminic diphenhydramine (118a) for a silicon atom leads to a total loss of histaminolytic activity190. Under the test conditions employed (Tyrode s solution 37 °C, pH 7.4), hydrolysis of siladiphenhydramine (118b) (cleavage of the Si-OC and Si-H bond) was so fast that no histaminolytic effect of the intact sila-drug could be detected. 

Acetylcholine is a neurohormone that enhances peristalsis, wakefulness, and memory and is essential for nerve transmission. A deficiency of brain cell receptors that bind acetylcholine—cholinergic receptors—contributes to the characteristic loss of memory in Alzheimer s disease. Cholinergic receptors are structurally similar to those that bind histamine. Therefore, antihistamines and cholinergic agents show overlapping activities. As a result, the antihistamine diphenhydramine has been used to treat insomnia and to combat motion sickness. 

Benztropine mesylate (cogentin, others), biperiden (akineton), procycUdine (kemadrin), and trihexyphenidyl hydrochloride (artane, others) are tertiary-amine muscarinic receptor antagonists (together with the ethanolamine antihistamine diphenhydramine [benadryl, others]) that gain access to the CNS and can therefore be used when anticholinergics are indicated to treat parkinsonism and the extrapyramidal side effects of antipsychotic drugs (see Chapter 20). 

Anticholinergics/ Antihistamines Diphenhydramine, dimenhydrinate and meclizine are antihistamines with anticholinergic effects. Anticholinergic drugs reduce motion sickness as well as emesis. 

Scientists at Lilly Research Laboratories synthesized more than 50 phenoxypropylamines derived from the antihistamine diphenhydramine (Benadryl) before discovering fluoxetine (21,22) (Fig. 21.2). The first of these compounds was nisoxetine, a potent SNRI (see Fig. 21.8) that was clinically developed but never marketed. Other derivatives that have since been marketed by Lilly include atomoxetine (a SNRI) and duloxetine (a NSRI). 

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