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Phenylephrine is a selective α1-adrenergic receptor agonist used primarily as a decongestant, as an agent to dilate the pupil, and to increase blood pressure. Phenylephrine is marketed as a substitute for the decongestant pseudoephedrine, though clinical studies differ regarding its effectiveness in this role.
Decongestant
Phenylephrine is used as a decongestant sold as an oral medicine, as a nasal spray, or as eye drops. It is now the most common over-the-counter decongestant in the United States; oxymetazoline is a more common nasal spray.
Oral phenylephrine is extensively metabolised by monoamine oxidase, an enzyme that is present in the intestinal wall and in the liver. Compared to intravenous pseudoephedrine, it has a reduced and variable bioavailability; only up to 38%. Because phenylephrine is a selective α-adrenergic receptor agonist it does not cause the release of endogenous noradrenaline. Nor does it increase the rate (chronotropy) and strength (inotropy) of heart contractions, as pseudoephedrine does.Phenylephrine may cause side effects such as headache, reflex bradycardia, excitability, restlessness and cardiac arrhythmias.
Hemorrhoid discomfort
This medication is used to temporarily relieve swelling, burning, pain, and itching caused by hemorrhoids. It works by temporarily narrowing the blood vessels in the area. This effect decreases swelling and discomfort. Some products may also contain substances (e.g., cocoa butter, hard fat, mineral oil, shark liver oil) that form a protective barrier to prevent too much irritating contact with stool.
Mydriatic
Phenylephrine is used as an eye drop to dilate the pupil to facilitate visualization of the retina. It is often used in combination with tropicamide as a synergist when tropicamide alone is not sufficient. Narrow-angle glaucoma is a contraindication to phenylephrine use. As a mydriatic, it is available in 2.5% and 10% minims.
Vasopressor
Phenylephrine is commonly used as a vasopressor to increase the blood pressure in unstable patients with hypotension, especially resulting from septic shock. Such use is common in anesthesia or critical-care practices; it is especially useful in counteracting the hypotensive effect of epidural and subarachnoid anesthetics, as well as the vasodilating effect of bacterial toxins and the inflammatory response in sepsis and systemic inflammatory response syndrome.
Substitute for pseudoephedrine
Pseudoephedrine and phenylephrine are both used as decongestants; and, until recently, pseudoephedrine was much more commonly available in the United States. This has changed because provisions of the Combat Methamphetamine Epidemic Act of 2005 placed restrictions on the sale of pseudoephedrine products to prevent the clandestine manufacture of methamphetamine. Since 2004, phenylephrine has been increasingly marketed as a substitute for pseudoephedrine; some manufacturers have changed the active ingredients of products to avoid the restrictions on sales. Phenylephrine has been off patent for some time, and many generic brands are available.
Questions about effectiveness
Pharmacists Leslie Hendeles and Randy Hatton of the University of Florida suggested in 2006 that oral phenylephrine is ineffective as a decongestant at the 10-mg dose used, arguing that the studies used for the regulatory approval of the drug in the United States in 1976 were inadequate to prove effectiveness at the 10-mg dose, and safety at higher doses.Other pharmacists have expressed concerns over phenylephrine's effectiveness as a nasal decongestant, and other clinicians have indicated concern for regulatory actions that reduced the availability of pseudoephedrine. A subsequent meta-analysis by the same researchers concluded that the evidence for its effectiveness is insufficient, though another meta-analysis published shortly thereafter by researchers from GlaxoSmithKline found the standard 10-mg dose to be significantly more effective than a placebo.
You should not use this medication if you are allergic to chlorpheniramine or phenylephrine.
Do not use this medicine if you have taken an MAO inhibitor in the past 14 days. A dangerous drug interaction could occur. MAO inhibitors include isocarboxazid, linezolid, phenelzine, rasagiline, selegiline, and tranylcypromine.
Ask a doctor or pharmacist if it is safe for you to take this medicine if you have:
asthma or COPD, cough with mucus, or cough caused by smoking, emphysema, or chronic bronchitis;
a blockage in your stomach or intestines;
kidney or liver disease;
high blood pressure, heart disease, coronary artery disease, or recent heart attack;
enlarged prostate or urination problems;
glaucoma;
diabetes;
epilepsy or other seizure disorder;
pheochromocytoma (an adrenal gland tumor);
overactive thyroid; or
if you take potassium (Cytra, Epiklor, K-Lyte, K-Phos, Kaon, Klor-Con, Polycitra, Urocit-K).
FDA pregnancy category C. It is not known whether chlorpheniramine and phenylephrine will harm an unborn baby. Do not use this medicine without your doctor's advice if you are pregnant.
It is not known whether chlorpheniramine and phenylephrine passes into breast milk or if it could harm a nursing baby. Antihistamines and decongestants may also slow breast milk production. Do not use this medicine without your doctor's advice if you are breast-feeding a baby.
Older adults may be more likely to have side effects from this medicine.
Artificially sweetened liquid cold medicine may contain phenylalanine. If you have phenylketonuria (PKU), check the medication label to see if the product contains phenylalanine.
This combination medication is used to temporarily relieve symptoms caused by the common cold, flu, allergies, or other breathing illnesses (such as sinusitis, bronchitis). Antihistamines help relieve watery eyes, itchy eyes/nose/throat, runny nose, and sneezing. Decongestants help to relieve stuffy nose and ear congestion symptoms.
If you are self-treating with this medication, carefully read the package instructions to be sure it is right for you before you start using this product. Some products have similar brand names but different active ingredients with different uses. Taking the wrong product could harm you. Ask your pharmacist if you have any questions about your product or its use.
Cough-and-cold products have not been shown to be safe or effective in children younger than 6 years. Therefore, do not use this product to treat cold symptoms in children younger than 6 years unless specifically directed by the doctor. Some products (including some long-acting tablets/capsules) are not recommended for use in children younger than 12 years. Ask your doctor or pharmacist for more details about using your product safely. Do not use this product to make a child sleepy.
These products do not cure or shorten the length of the common cold and may cause serious side effects. To decrease the risk for serious side effects, carefully follow all dosage directions. Do not give other cough-and-cold medication that might contain the same or similar ingredients (see also Drug Interactions section). Ask the doctor or pharmacist about other ways to relieve cough and cold symptoms (such as drinking enough fluids, using a humidifier or saline nose drops/spray).
How to use Dimetapp Cold-Allergy (PE) Oral
Take this medication by mouth as directed by your doctor. If you are self-treating, follow all directions on the product package. If you are uncertain about any of the information, ask your doctor or pharmacist.
This medication may be taken with food if stomach upset occurs. Drink plenty of fluids unless otherwise directed by your doctor.
If you are using the liquid form of this medication, carefully measure the dose using a special measuring device/spoon. Do not use a household spoon because you may not get the correct dose. If your liquid form is a suspension, shake the bottle well before each dose.
Do not crush or chew extended-release tablets or capsules. Doing so can release all of the drug at once, increasing the risk of side effects. Also, do not split extended-release tablets unless they have a score line and your doctor or pharmacist tells you to do so. Swallow the whole or split tablet without crushing or chewing.
If you are using chewable tablets, chew each tablet thoroughly before swallowing.
If you are using a product made to dissolve in the mouth (tablets/strips), dry your hands before handling the medication. Place each dose on the tongue and allow to dissolve completely, then swallow it with saliva or with water.
Dosage is based on the product you are taking and your age, medical condition, and response to treatment. Do not increase your dose or take this medication more often than directed without your doctor's approval. Improper use (abuse) of this medication may result in serious harm (such as hallucinations, seizure, death).
If your doctor directs you to take this medication daily, take it regularly to get the most benefit from it. To help you remember, take it at the same time(s) each day.
Tell your doctor if your condition persists for more than 1 week, if it worsens, or if it occurs with fever, rash, or persistent headache. These may be symptoms of a serious medical problem and should be checked by a doctor.
Drowsiness, dizziness, dry mouth/nose/throat, headache, upset stomach, constipation, or trouble sleeping may occur. If any of these effects persist or worsen, tell your doctor or pharmacist promptly.
If your doctor has directed you to use this product, remember that he or she has judged that the benefit to you is greater than the risk of side effects. Many people using the product do not have serious side effects.
Tell your doctor immediately if any of these unlikely but serious side effects occur: mental/mood changes (such as confusion, hallucinations), ringing in the ears, difficulty urinating, vision changes (such as blurred/double vision).
Seek immediate medical attention if any of these rare but very serious side effects occur: fast/irregular heartbeat, seizure.
A very serious allergic reaction to this drug is rare. However, seek immediate medical attention if you notice any symptoms of a serious allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.
This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.
Before taking this medication, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.
If you have any of the following health problems, consult your doctor or pharmacist before using this product: cough with a lot of mucus, chronic cough (such as with asthma, emphysema, smoking), diabetes, a certain eye condition (glaucoma), heart problems (such as heart attack, chest pain, heart failure), fast/irregular heartbeat, high blood pressure, liver disease, overactive thyroid (hyperthyroidism), difficulty urinating (such as due to enlarged prostate).
This drug may make you dizzy. Do not drive, use machinery, or do any activity that requires alertness until you are sure you can perform such activities safely. Limit alcoholic beverages.
This medicine may contain sugar, alcohol, or aspartame. Caution is advised if you have diabetes, alcohol dependence, liver disease, phenylketonuria (PKU), or any other condition that requires you to limit/avoid these substances in your diet. Ask your doctor or pharmacist about using this product safely.
Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).
Older adults may be more sensitive to the side effects of this medication, especially fast/irregular heartbeat, dizziness, problems urinating, trouble sleeping, or confusion.
Children may be more sensitive to the side effects of this medication, especially agitation.
During pregnancy, this medication should be used only when clearly needed. Discuss the risks and benefits with your doctor.
Pseudoephedrine passes into breast milk. Consult your doctor before breast-feeding.
The effects of some drugs can change if you take other drugs or herbal products at the same time. This can increase your risk for serious side effects or may cause your medications not to work correctly. These drug interactions are possible, but do not always occur. Your doctor or pharmacist can often prevent or manage interactions by changing how you use your medications or by close monitoring.
To help your doctor and pharmacist give you the best care, be sure to tell your doctor and pharmacist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products) before starting treatment with this product. While using this product, do not start, stop, or change the dosage of any other medicines you are using without your doctor's approval.
Some products that may interact with this drug include: antihistamines applied to the skin (such as diphenhydramine cream, ointment, spray), blood pressure medications (especially reserpine, guanethidine, methyldopa, beta blockers such as atenolol, or calcium channel blockers such as nifedipine).
Taking MAO inhibitors with this medication may cause a serious (possibly fatal) drug interaction. Avoid taking MAO inhibitors (isocarboxazid, linezolid, methylene blue, moclobemide, phenelzine, procarbazine, rasagiline, selegiline, tranylcypromine) during treatment with this medication. Most MAO inhibitors should also not be taken for two weeks before treatment with this medication. Ask your doctor when to start or stop taking this medication.
Tell your doctor or pharmacist if you are taking other products that cause drowsiness including alcohol, antihistamines (such as cetirizine, diphenhydramine), drugs for sleep or anxiety (such as alprazolam, diazepam, zolpidem), muscle relaxants, and narcotic pain relievers (such as codeine).
Check the labels on all your medicines (such as cough-and-cold products, diet aids) because they may contain ingredients that could affect your blood pressure or cause drowsiness. Ask your pharmacist about using those products safely.
This medication may interfere with certain medical/laboratory tests (including brain scan for Parkinson's disease), possibly causing false test results. Make sure laboratory personnel and all your doctors know you use this drug.
This document does not contain all possible drug interactions. Keep a list of all the products you use. Share this list with your doctor and pharmacist to lessen your risk for serious medication problems.
If overdose is suspected, contact a poison control center or emergency room immediately. Symptoms of overdose may include: agitation, confusion, hallucinations, seizures.
Notes
This medication is for temporary use only. Do not use for more than 7 days without first consulting your doctor.
Missed Dose
If you are taking this product on a regular schedule and miss a dose, take it as soon as you remember. If it is near the time of the next dose, skip the missed dose and resume your usual dosing schedule. Do not double the dose to catch up.
Storage
Different brands of this medication have different storage needs. Check the product package for instructions on how to store your brand, or ask your pharmacist. Keep all medications away from children and pets.
Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Properly discard this product when it is expired or no longer needed. Consult your pharmacist or local waste disposal company.
Information last revised October 2013. Copyright(c) 2013 First Databank, Inc.
