Pharmacological Profiles of Several Common Drugs

2.3 Profile of Pheniramine Maleate (31)

• Chemical name: (3RS)-N,N-Dimethyl-3-phenyl-3-(pyridine-2-yl)propan-1-amine(Z)-butenedioate
• Empirical formula: C₂₀H₂₄N₂O₄
• Chemical structure:

Figure 2.3:Structure of Pheniramine Maleate

2.3.1 Physical properties

• Molecular weight: 356.4
• Appearance and colour: White or almost white crystalline powder.
• Solubility: Very soluble in water, freely soluble in ethanol (96 %)in methanol and in methylene chloride.
• Therapeutic category:Pheniramine maleate belongs to H1-antagonist pharmacological group on the basis of mechanism of action and also classified in Antihistamine, Decongestant.
• Dosage: Tablet , Powder, Solution

2.3.2 Pharmacology

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.

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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)

• Chemical name:(R)-(-)-1-(3-Hydroxyphenyl)-2-methylaminoethanol hydrochloride
• Empirical formula:C₉H₁₃NO₂HCL
• Chemical structure:

Figure 2.4 : Structure of Phenylephrine Hydrochloride

2.4.1 Physical properties

• Molecular weight:203.67
• Appearance and colour: White or practically white odourless crystals
• Solubility: Freely soluble in water and alcohol
• Therapeutic category: Phenylephrine is a sympathomimetic amine that acts predominantly on α-adrenergic receptors. It is mainly used to treat nasal congestion, but may also be useful in treating hypotension and shock, hypotension during spinal anaesthesia, prolongation of spinal anaesthesia, paroxysmal supraventricular tachycardia, symptomatic relief of external or internal hemorrhoids, and to increase blood pressure as an aid in the diagnosis of heart murmurs.
• Dosage: Cream, Solution, Ointment, Injection, Liquid, Tablet, Suppository

2.4.2 Pharmacology

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)

• Chemical name:(1R,9R,10R) – 4 – methoxy – 17 – methyl – 17 azatetracyclo[7.5.3.0{1,10}.0{2,7}]heptadeca-2,4,6-triene
• Empirical formula:C₁₈H₂₅NO

• Chemical structure:

Figure 2.5 : Structure of Dextromethorphan

2.5.1 Physical properties

• Molecular weight:271.39
• Appearance and colour: It is a White crystalline powder
• Solubility: 1-5 g/100 mL at 21 ºC
• Therapeutic category: Dextromethorphan usually used in the treatment of respiratory infections and allergic conditions
• Dosage: Tablet , Syrup, Capsule, Suspension

2.5.2 Pharmacology

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)

• Chemical name: 2-(diphenylmethoxy)-N,N-dimethylethanamine
• Empirical formula:C₁₇H₂₁NO HCL

• Chemical structure:

Figure 2.6 : Structure of Diphenhydramine

2.6.1 Physical properties

• Molecular weight:291.82
• Appearance and colour: It is a White crystalline powder
• Solubility: Soluble in DMSO, acetone, water
• Therapeutic category: Diphenhydramineis a first-generationantihistamine possessing anticholinergic, antitussive, antiemetic, and sedative properties that is mainly used to treat allergies. It is also used in the management of drug-induced parkinsonism and other extrapyramidal symptoms. The drug has a strong hypnotic effect and is FDA-approved as a non-prescription sleep aid, especially in the form of diphenhydramine citrate
• Dosage: Capsule

2.6.2 Pharmacology

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