27 Mar 2018
2.3 Profile of Pheniramine Maleate (31)
Figure 2.3:Structure of Pheniramine Maleate
2.3.1 Physical properties
Pheniramine maleate is an antihistamine used for alleviation of allergy symptoms. Manufacturers frequently list the over-the-counter medication as pheniramine maleate or a derivative. Drug industries also often combine the formulation with other medications for relief of other symptoms. Consumers can generally find the ingredient in an oral solution or tablet form. Certain ophthalmic solutions also contain pheniramine maleate, which provides relief from allergy symptoms associated with the eyes.
Allergic reactions are autoimmune responses to certain antigens. When allergens enter the bloodstream, the body releases histamine, which binds with and activates receptor sites, located throughout the body, producing physical symptoms. The pharmacological action of pheniramine maleate involves blocking the receptor sites for the histamine H1, found in the heart, central nervous system, smooth muscle, and vascular endothelium cells. Blocking the receptor sites reduces or inhibits the symptoms.
The antihistamine is frequently used for seasonal allergies, such as hay fever, or environmental allergies, such as animal dander. By blocking histamine receptor sites, pheniramine maleate can reduce or eliminate itching, watery eyes, runny noses, and skin irritations. Allergy related skin irritations might include the itching, redness, and swelling associated with eczema or uticaria, commonly referred to as hives (40).
The medication may produce a sedative effect when binding to sites in the central nervous system. It also may produce an anticholinergic effect by dilating or relaxing smooth muscle. These side effects sometimes allow pheniramine maleate to be used as treatment for motion sickness or the inner ear condition known as Meniere’s disease.
2.4 Profile of Phenylephrine Hydrochloride (78)
Figure 2.4 : Structure of Phenylephrine Hydrochloride
2.4.1 Physical properties
In general, α1-adrenergic receptors mediate contraction and hypertrophic growth of smooth muscle cells. α1-receptors are 7-transmembrane domain receptors coupled to G proteins, Gq/11. Three α1-receptor subtypes, which share approximately 75% homology in their transmembrane domains, have been identified: α1A (chromosome 8), α1B (chromosome 5), and α1D (chromosome 20). Phenylephrine appears to act similarly on all three receptor subtypes. All three receptor subtypes appear to be involved in maintaining vascular tone. The α1A-receptor maintains basal vascular tone while the α1B-receptor mediates the vasocontrictory effects of exogenous α1-agonists. Activation of the α1-receptor activates Gq-proteins, which results in intracellular stimulation of phospholipases C, A2, and D. This results in mobilization of Ca2+ from intracellular stores, activation of mitogen-activated kinase and PI3 kinase pathways and subsequent vasoconstriction. Phenylephrine produces its local and systemic actions by acting on α1-adrenergic receptors peripheral vascular smooth muscle. Stimulation of the α1-adrenergic receptors results in contraction arteriolar smooth muscle in the periphery. Phenylephrine decreases nasal congestion by acting on α1-adrenergic receptors in the arterioles of the nasal mucosa to produce constriction; this leads to decreased edema and increased drainage of the sinus cavities.
2.5 Profile of Dextromethorphan (79)
Figure 2.5 : Structure of Dextromethorphan
2.5.1 Physical properties
Dextromethorphan is an opioid-like drug that binds to and acts as antagonist to the NMDA glutamatergic receptor, it is an agonist to the opioid sigma 1 and sigma 2 receptors, it is also an alpha3/beta4 nicotinic receptor antagonist and targets the serotonin reuptake pump. Dextromethorphan is rapidly absorbed from the gastrointestinal tract, where it enters the bloodstream and crosses the blood-brain barrier. The first-pass through the hepatic portal vein results in some of the drug being metabolized into an active metabolite of dextromethorphan, dextrorphan, the 3-hydroxy derivative of dextromethorphan.
2.6 Profile of Diphenhydramine (80)
2.6.1 Physical properties
Diphenhydramine is an inverse agonist of the histamineH1receptor. It is a member of the ethanolamine class of antihistaminergic agents. By blocking the effects of histamine on the capillaries, it can reduce the intensity of allergic symptoms. Diphenhydramine also crosses the blood–brain barrier (BBB) and antagonizes the H1 receptors centrally. Its effects on central H1 receptors cause drowsiness.
Like many other first-generation antihistamines, diphenhydramine is also a potent antimuscarinic (a competitive antagonist of muscarinic acetylcholine receptors), and, as such, at high doses can cause anticholinergic syndrome. The utility of diphenhydramine as
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