Phenylephrine is a selective -adrenergic receptor agonist? 1 of the phenethylamine class is used primarily as a decongestant, as an agent to dilate the pupil, to increase blood pressure, and to relieve hemorrhoids. Phenylephrine is marketed as an alternative to pseudoephedrine decongestant, although clinical trials show phenylephrine, taken orally at the recommended dosage, to be no more effective than placebo for allergy relief. Phenylephrine can also cause a decrease in heart rate through reflex bradycardia.
Video Phenylephrine
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Decongestant
Phenylephrine is used as a decongestant sold as an oral medication or as a nasal spray. This is a common ingredient in over-the-counter decongestants in the United States. Other decongestants include oxymetazoline and pseudoephedrine.
Phenylephrine is used as an alternative to pseudoephedrine in decongestant drugs because of the use of pseudoephedrine in the manufacture of illegal methamphetamine. Its efficacy as an oral decongestant has been questioned, with some independent studies have recently found that it does provide more relief for clogged sinuses than placebo.
Pharmacist Leslie Hendeles and Randy Hatton of the University of Florida suggested in 2006 that oral phenylephrine was ineffective as a decongestant at the 10-mg dose used, arguing that the research used for drug regulatory approval in the United States in 1976 was inadequate. to prove its effectiveness at a dose of 10 mg, and safety at higher doses.
A 2007 meta-analysis by Hatton et al. concluded that evidence of its effectiveness was insufficient, although another meta-analysis published shortly thereafter by researchers from GlaxoSmithKline found standard 10 mg doses were significantly more effective than placebo; However, the fact that GSK markets many products containing phenylephrine has generated some speculation about selective publishing and other controversial techniques. A 2007 study by Wyeth Consumer Healthcare noted that 7 studies available in 1976 supported the efficacy of phenylephrine at a dose of 10 mg.
Two studies published in 2009 examined the effects of phenylephrine on the symptoms of allergic rhinitis by exposing the sufferer to pollen in a controlled indoor environment. No study was able to distinguish the effects of phenylephrine or placebo. Pseudoephedrine and loratadine-montelukast therapy were found to be much more effective than phenylephrine and placebo.
The Food and Drug Administration has stood at the 1976 agreement of phenylephrine for nasal congestion as the debate continues.
Hemorrhoids
Hemorrhoids are caused by swollen veins in the rectal area. Phenylephrine can be used topically to prevent hemorrhoids symptoms. Phenylephrine causes the narrowing of smooth muscle of the blood vessels and is often used in the treatment of possible hemorrhoids to narrow the swollen veins and alleviate the accompanying pain. However, veins - unlike arteries - contain less vascular smooth muscle in their walls so that the mechanism by which pain relief is achieved may be related to something other than vascular changes only. Products for treatment may also include substances that will form a protective barrier over the inflamed area, thus reducing the pain when dirt is passed.
Dilated pupil
Phenylephrine is used as eye drops to dilate the pupils to facilitate visualization of the retina. It is often used in combination with tropicamide as synergistic when tropicamide alone is not enough. Narrow angle glaucoma is contraindicated for the use of phenylephrine. As mydriatic, it is available in 2.5% and 10% minims. Phenylephrine eye drops applied to eyes after topical anesthesia is applied.
Vasopressor
Phenylephrine is usually used as a vasopressor to increase blood pressure in patients who are unstable with hypotension, mainly due to septic shock. Such use is common in the practice of anesthesia or critical care; it is particularly useful in counteracting the hypotensive effects of epidural and subarachnoid anesthesia, as well as the vasodilatory effects of bacterial toxins and the inflammatory response to sepsis and systemic inflammatory response syndrome. The half-life of phenylephrine elimination is about 2.5 to 3.0 hours. The clinical effects of a single intravenous bolus dose of phenylephrine are short-lived and need to be repeated every 10-15 minutes. Generally the drug is given as intravenous infusion of careful titration with a syringe pump or volumetric pump.
Because of its vasoconstrictive effect, phenylephrine can cause severe necrosis if it infilts surrounding tissue. Because of this, it must be provided through a central line if at all possible. Damage can be prevented or reduced by infiltration of tissue with phentolamine alpha blocker by subcutaneous injection.
Phenylephrine hydrochloride at 0.25% is used as a vasoconstrictor in some suppository formulations.
Recently, Phenylephrine has been used to treat conditions of orthostatic intolerance such as Postural Orthostatic Tachycardia Syndrome - in which the activation of alpha venous adrenoceptors 1 increases venous return and increased symptoms.
Priapism
Phenylephrine is used by urologists to abort priapism. Diluted with normal saline and injected directly into the corpora cavernosa. The mechanism of action is to cause narrowing of blood vessels that enter the penis, causing blood flow to decrease and eliminate priapism. Injection is given every 3-5 minutes. If priapism is not resolved within 1 hour, other forms of therapy are considered.
Maps Phenylephrine
Side effects
Heart
The main side effect of phenylephrine is high blood pressure. People with high blood pressure are usually advised to avoid products that contain it. Since this drug is a sympathomimetic amine without beta-adrenergic activity, it does not increase the contractility and output power of the heart muscle. This can increase blood pressure resulting in a slow heart rate through vascular (carotid-dependent) baroreceptor stimulation. The common side effects during IV administration are reflex bradycardia. Low concentration eye drops do not cause changes in blood pressure and changes with higher doses do not last long.
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Prostate hyperplasia may also be aggravated by use, and chronic use may lead to rebound hyperemia. Persons with a history of anxiety or panic disorder, or on anticonvulsant drugs for epilepsy should not take this substance. Drug interactions may produce seizures. Some patients have been shown to have abdominal pain, severe abdominal cramps, and vomiting problems connected to taking this drug.
Phenylephrine is the category of pregnancy C. Due to the lack of studies conducted on animals and in humans, it is not known whether there is a danger to the fetus. Phenylephrine should only be given to pregnant women who have a clear need.
Prolonged use may lead to medicamentous rhinitis, a condition of nasal congestion.
Interactions
Increased blood pressure effects of phenylephrine may be enhanced by drugs such as monoamine oxidase inhibitors, tricyclic antidepressants, and hydrocortisone. Patients taking these drugs may require a lower dose of phenylephrine to achieve a similar increase in blood pressure.
Drugs that can reduce the effects of phenylephrine may include calcium channel blockers, ACE inhibitors and benzodiazepines. Patients taking these drugs may require a higher phenylephrine dose to achieve a comparable increase in blood pressure.
Action mechanism
Oral phenylephrine is extensively metabolized by monoamine oxidase, an enzyme present outside the cell, throughout the body. Compared with intravenous pseudoephedrine, phenylephrine has reduced bioavailability and variables; only up to 38%. Phenylephrine is a sympathomimetic drug, which means mimicking the action of epinephrine (commonly known as adrenaline) or norepinephrine. Phenylephrine selectively binds to alpha receptors that cause narrowed blood vessels. Phenylephrine can cause side effects such as headache, reflex bradycardia, excitability, anxiety and cardiac arrhythmias. Phenylephrine is not recommended for use in patients with hypertension.
While pseudoephedrine causes both vasoconstriction and increased mucociliary clearance through nonspecific adrenergic activity, selective agonist phenotrines cause vasoconstriction alone, creating differences in their method of action.
Substitute for pseudoephedrine
Pseudoephedrine and phenylephrine are both used as decongestants; and, to date, pseudoephedrine is much more commonly available in the United States. This has changed because the 2005 Meterfetamin Battle Epidemic Act stipulates restrictions on the sale of pseudoephedrine products to prevent the manufacture of spinaches secretly. Since 2004, phenylephrine has been increasingly marketed as a substitute for pseudoephedrine; some manufacturers have changed the product's active ingredients to avoid sales restrictions. Phenylephrine has been patented for some time, and many generic brands are available.
References
External links
- Drugs.com - Phenylephrine
- MedlinePlus: Phenylephrine
- US. National Drug Library: Drug Information Portal - Phenylephrine
- Neosynephrine Intravenous Inlution Guidelines: [1]
Source of the article : Wikipedia
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