Phenylephrine Actions

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Actions of Phenylephrine in details

infoThe action of the drug on the human body is called Pharmacodynamics in Medical terminology. To produce its effect and to change the pathological process that is happening the body and to reduce the symptom or cure the disease, the medicine has to function in a specific way. The changes it does to the body at cellular level gives the desired result of treating a disease. Drugs act by stimulating or inhibiting a receptor or an enzyme or a protein most of the times. Medications are produced in such a way that the ingredients target the specific site and bring about chemical changes in the body that can stop or reverse the chemical reaction which is causing the disease.
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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.

How should I take Phenylephrine?

This section provides information on the proper use of a number of products that contain Phenylephrine. It may not be specific to Phenylephrine. Please read with care.

To use the nose drops:

  • Blow your nose gently. Tilt the head back while standing or sitting up, or lie down on a bed and hang head over the side. Place the drops into each Phenylephrine and keep the head tilted back for a few minutes to allow the medicine to spread throughout the nose.
  • Rinse the dropper with hot water and dry with a clean tissue. Replace the cap right after use.
  • To avoid spreading the infection, do not use the container for more than one person.

To use the nose spray:

  • Blow your nose gently. With the head upright, spray the medicine into each Phenylephrine. Sniff briskly while squeezing the bottle quickly and firmly. For best results, spray once or twice into each Phenylephrine and wait 3 to 5 minutes to allow the medicine to work. Then, blow your nose gently and thoroughly. Repeat until the complete dose is used.
  • Rinse the tip of the spray bottle with hot water, taking care not to suck water into the bottle, and dry with a clean tissue. Replace the cap right after use.
  • To avoid spreading the infection, do not use the container for more than one person.

To use the nose jelly:

  • Blow your nose gently. Wash your hands before applying the medicine. With your finger, place a small amount of jelly (about the size of a pea) up each Phenylephrine. Sniff it well back into the nose.
  • Wipe the tip of the tube with a clean, damp tissue and replace the cap right after use.

Use this medicine only as directed. Do not use more of it, do not use it more often, and do not use it for longer than 3 days without first checking with your doctor. To do so may make your runny or stuffy nose worse and may also increase the chance of side effects.

Dosing

The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

  • For stuffy nose:
    • For nose jelly dosage form:
      • Adults—Use a small amount in the nose every three or four hours as needed.
      • Children—Use is not recommended.
    • For nose drops dosage form:
      • Adults and children 12 years of age and older—Use two or three drops of a 0.25 to 0.5% solution in the nose every four hours as needed.
      • Children 6 to 12 years of age—Use two or three drops of a 0.25% solution in the nose every four hours as needed.
      • Children 4 to 6 years of age—Use two or three drops of a 0.125 or 0.16% solution in the nose every four hours as needed.
      • Children and infants up to 4 years of age—Use is not recommended.
    • For nose spray dosage form:
      • Adults and children 12 years of age and older—Use two or three sprays of a 0.25 to 0.5% solution in the nose every four hours as needed.
      • Children 6 to 12 years of age—Use two or three sprays of a 0.25% solution in the nose every four hours as needed.
      • Children 4 to 6 years of age—Use and dose must be determined by your doctor.
      • Children and infants up to 4 years of age—Use is not recommended.

Missed Dose

If you miss a dose of this medicine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

Storage

Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.

Keep out of the reach of children.

Do not keep outdated medicine or medicine no longer needed.

Phenylephrine administration

infoAdministration of drug is important to know because the drug absorption and action varies depending on the route and time of administration of the drug. A medicine is prescribed before meals or after meals or along with meals. The specific timing of the drug intake about food is to increase its absorption and thus its efficacy. Few work well when taken in empty stomach and few medications need to be taken 1 or 2 hrs after the meal. A drug can be in the form of a tablet, a capsule which is the oral route of administration and the same can be in IV form which is used in specific cases. Other forms of drug administration can be a suppository in anal route or an inhalation route.
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Use Phenylephrine eyedrops exactly as directed by your doctor, or follow the directions that accompany the package. If you do not understand these instructions, ask your doctor, pharmacist, or nurse to explain them to you.

Wash your hands before and after using the eyedrops.

If you wear contact lenses, remove them before applying Phenylephrine ophthalmic. Ask your doctor if contact lenses can be reinserted after application of the medication. Phenylephrine ophthalmic may contain a preservative (benzalkonium chloride), which may cause discoloration of contact lenses.

To apply the eyedrops:

  • Tilt the head back slightly and pull down on the lower eyelid. Position the dropper above the eye. Look up and away from the dropper. Squeeze out a drop and close the eye. Apply gentle pressure to the inside corner of the eye (near the nose) for about 1 minute to prevent the liquid from draining down the tear duct. Repeat the process in the other eye if needed.

Do not use Phenylephrine ophthalmic more often or continuously for longer than 48 to 72 hours without consulting a doctor. Chronic use of this medication may damage the blood vessels (veins and arteries) in the eyes. Consult a doctor if your symptoms do not improve or appear to worsen.

Do not touch the dropper to any surface, including the eyes or hands. The dropper is sterile. If it becomes contaminated, it could cause an infection in the eye.

Do not use any eyedrop that is discolored or has particles in it.

Store Phenylephrine ophthalmic at room temperature away from moisture and heat. Keep the bottle properly capped.

Phenylephrine pharmacology

infoPharmacokinetics of a drug can be defined as what body does to the drug after it is taken. The therapeutic result of the medicine depends upon the Pharmacokinetics of the drug. It deals with the time taken for the drug to be absorbed, metabolized, the process and chemical reactions involved in metabolism and about the excretion of the drug. All these factors are essential to deciding on the efficacy of the drug. Based on these pharmacokinetic principles, the ingredients, the Pharmaceutical company decides dose and route of administration. The concentration of the drug at the site of action which is proportional to therapeutic result inside the body depends on various pharmacokinetic reactions that occur in the body.
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Mechanism Of Action

Phenylephrine hydrochloride is an a-1 adrenergic receptor agonist.

Pharmacodynamics

Interaction of Phenylephrine with a1-adrenergic receptors on vascular smooth muscle cells causes activation of the cells and results in vasoconstriction. Following Phenylephrine hydrochloride intravenous administration, increases in systolic and diastolic blood pressures, mean arterial blood pressure, and total peripheral vascular resistance are observed. The onset of blood pressure increase following an intravenous bolus Phenylephrine hydrochloride administration is rapid, typically within minutes. As blood pressure increases following intravenous administration, vagal activity also increases, resulting in reflex bradycardia.

Phenylephrine has activity on most vascular beds, including renal, pulmonary, and splanchnic arteries.

Pharmacokinetics

Following an intravenous infusion of Phenylephrine hydrochloride, the observed effective halflife was approximately 5 minutes. The steady-state volume of distribution of approximately 340 L suggests a high distribution into organs and peripheral tissues. The average total serum clearance is approximately 2100 mL/min. The observed Phenylephrine plasma terminal elimination half-life was 2.5 hours.

Phenylephrine is metabolized primarily by monoamine oxidase and sulfotransferase. After intravenous administration of radiolabeled Phenylephrine, approximately 80% of the total dose was eliminated within first 12 h; and approximately 86% of the total dose was recovered in the urine within 48 h. The excreted unchanged parent drug was 16% of the total dose in the urine at 48 h post intravenous administration. There are two major metabolites, with approximately 57 and 8% of the total dose excreted as m-hydroxymandelic acid and sulfate conjugates, respectively. The metabolites are considered not pharmacologically active.

Clinical Studies

The evidence for the efficacy of Phenylephrine is derived from studies of Phenylephrine hydrochloride in the published literature. The literature support includes 16 studies evaluating the use of intravenous Phenylephrine to treat hypotension during anesthesia. The 16 studies include 9 studies where Phenylephrine was used in low-risk (ASA 1 and 2) pregnant women undergoing neuraxial anesthesia during Cesarean delivery, 6 studies in non-obstetric surgery under general anesthesia, and 1 study in non-obstetric surgery under combined general and neuraxial anesthesia. Phenylephrine has been shown to raise systolic and mean blood pressure when administered either as a bolus dose or by continuous infusion following the development of hypotension during anesthesia.



References

  1. NCIt. "Phenylephrine: NCI Thesaurus (NCIt) provides reference terminology for many systems. It covers vocabulary for clinical care, translational and basic research, and public information and administrative activities.". https://ncit.nci.nih.gov/ncitbrowser... (accessed September 17, 2018).
  2. EPA DSStox. "Phenylephrine: DSSTox provides a high quality public chemistry resource for supporting improved predictive toxicology.". https://comptox.epa.gov/dashboard/ds... (accessed September 17, 2018).
  3. EPA Chemicals under the TSCA. "Benzenemethanol, 3-hydroxy-.alpha.-[(methylamino)methyl]- , hydrochloride (1:1), (.alpha.R)-: The Chemical Data Reporting under the Toxic Substances Control Act (TSCA) contains chemical physical description and chemical use categories.". http://www.epa.gov/chemical-data-rep... (accessed September 17, 2018).

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The results of a survey conducted on ndrugs.com for Phenylephrine are given in detail below. The results of the survey conducted are based on the impressions and views of the website users and consumers taking Phenylephrine. We implore you to kindly base your medical condition or therapeutic choices on the result or test conducted by a physician or licensed medical practitioners.

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Information checked by Dr. Sachin Kumar, MD Pharmacology

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