Anticholinergics antihistamines and

Sedation is often seen in adults as a side effect of treatment. It is presumably related to a combination of anticholinergic, antihistaminic, and serotonergic effects of this medication. Sedation is seen more often with the tertiary amines than with the secondary amines (Baldessarini, 1996). 

Bupropion, the only marketed aminoketone antidepressant, also has a side-effect profile different from the other classes of antidepressants. It is essentially devoid of anticholinergic, antihistaminic, and orthostatic hypotensive effects. Its principal adverse effects are consistent with its indirect agonism of dopamine and NE via uptake inhibition and include the following ... 

Benztropine Mesylate, USP. Benztropine mesylate. 3o-(diphenylmethoxy)-1 otH.SatH-ttopane methane.sulfonaic (Cogentin), has anticholinergic, antihistaminic. and local anesthetic properties. Its anticholineigic effect makes it applicable as an antiparkinsonian agent. It is about as potent an anticholinergic as atropine and shares some of the side effects of this drug, such as mydriasis and dryness of mouth. Importantly, however, it does not produce central stimulation but instead exerts the characteristic. sedative effect of the antihistamine.s. 

Antihistamines such as diphenhydramine are known for their sedating properties and are frequently used over-the-counter medications (usual doses 25-50 mg) for difficulty sleeping. Diphenhydramine is approved by the FDA for the treatment of insomnia and can be effective at reducing sleep latency and increasing sleep time.43 However, diphenhydramine produces undesirable anticholinergic effects and carryover sedation that limit its use. As with TCAs and BZDRAs, diphenhydramine should be used with caution in the elderly. Valerian root is an herbal sleep remedy that has inconsistent effects on sleep but may reduce sleep latency and efficiency at commonly used doses of 400 to 900 mg valerian extract. Ramelteon, a new melatonin receptor agonist, is indicated for insomnia characterized by difficulty with sleep onset. The recommended dose is 8 mg at bedtime. Ramelteon is not a controlled substance and thus may be a viable option for patients with a history of substance abuse. 

Medications for symptomatic relief from vertigo consist of antiemetics, benzodiazepines and antihistamines. They are all mostly aimed at the psychological consequences of dizziness and can all have highly unfavourable side effects, for example, sedation, anticholinergic effects and insomnia. The psychological consequences of dizziness in elderly should rather be treated with information about the condition, supportive help actions and increased social activities, than with drugs. 

Ethers are stable toward hydrolysis, yet are hydrolyzed under severe conditions of acidity and temperature. Furthermore, the presence of certain moieties can decrease the high stability of ethers. In the case of aminoalkyl benzhydryl ethers of the general structure (aryl)2CH-0-(CH2)n-NRR, the decrease in stability becomes marked enough to be of pharmaceutical and even pharmacological relevance. This structural motif is a component of various drugs, including some well-known antihistamines and anticholinergics, e.g., diphenhydramine, orphenadrine, and chlorphenoxamine. 

Cyclizine exhibits antihistamine and anticholinergic action and is used for vomiting and diarrhea. The exact mechanism of action is not known. Synonyms of this drug are marezine and migril. 

Drugs that may be affected by dronabinol include amphetamines, cocaine, sympathomimetics, anticholinergics, antihistamines, tricyclic antidepressants, alcohol, sedatives, hypnotics, psychomimetics, disulfiram, fluoxetine, and theophylline. 

Hydroxyzine hydrochloride Atarax, Vistarit) is the antihistamine with the greatest use in the treatment of anxiety. It is often used to reduce the anxiety that is associated with anesthesia and surgery. It also produces sedation, dries mucous membranes (via an anticholinergic mechanism), and has antiemetic activity. A more extensive discussion of the pharmacology of the Hj-receptor antagonists is found in Chapter 38. 

Another important use of Hj-antagonists is in the treatment of motion sickness. Diphenhydramine (Benadryl), dimenhydrinate (Dramamine), cyclizine (Marezine), and meclizine (Antivert) have anticholinergic activity and are the preferred antihistaminic agents for reducing the symptoms of motion sickness. 

Geriatric Considerations - Summary Brompheniramine is a first-generation al-kylamine antihistamine with potent Hj receptor antagonism, it has anticholinergic activity and can cause somnolence. Older adults taking this drug are at risk of dizziness and hypotension. 

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. 

Mechanism of Action An antihistamine and anticholinergicthat competes for H,-receptor sites on effector cells of the G1 tract, blood vessels, and respiratory tract. The anticholinergic action diminishesvestibular stimulation and depresses labyrinthine function. Therapeutic Effect Prevents symptoms of motion sickness. Pharmacokinetics Well absorbed following PO administration. Metabolized in liver. Excreted in urine. Half-life Unknown. 

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. 

Olanzapine is metabolized by several pathways and is therefore unlikely to be affected by concurrent administration of other medications. Because olanzapine does not appear to inhibit any cytochrome P450 enzymes, it should not increase the availability of other medications through inhibition of such enzymes. Additive pharmacodynamic effects are expected if olanzapine is combined with medications that also have anticholinergic, antihistaminic, or aj-adrenergic side effects. 

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 ... 

Droperidol and hydroxyzine (25-50 mg IM) is sometime used for their antiemetic activity. Hydroxyzine has antianxiety, antihistaminic and anticholinergic properties also. 

Antihistaminics are better tolerated by elderly patients who do not tolerate anticholinergics. Antihistaminics do not cause blurring of vision and xerostomia and also possess some central anticholinergic properties. 

CNS disorders Scopolamine and hyoscine are effectively used in the treatment of nausea, vomiting and motion sickness. Centrally acting anticholinergic/ antihistaminics e.g. trihexyphenidyl are used in parkinsonism. 

Clemastine, 1.34 mg every 12 hours Tavist Allergy have minimal anticholinergic effects and are therefore associated with a lower incidence of sedation. Occasionally, symptoms unrelieved by the antihistamine respond to the addition of a sympathomimetic decongestant. OTC sale of products containing pseudoephedrine is restricted (see comments under Decongestants, systemic). 

---