The most important factors that influence phenylephrine dosage are the condition being treated, the form of the drug and the patient’s age. Sometimes the patient's response to the medication could be useful in determining the right dose. Alternately, the recommended amount might be affected by medical conditions or by the use of other medications.
Phenylephrine can be an over-the-counter nasal decongestant used for older children and adults. It also comes in an ophthalmic solution to treat dry or irritated eyes or to prepare the eyes for surgery. Also, there are a variety of solutions that are injected intramuscularly (IM) or delivered intravenously (IV) to address shock, hypotension, and supraventricular tachycardia.
To treat nasal congestion, adults and children over 12 are directed to take 10-20 milligrams (mg) every four to six hours. The phenylephrine dosage might change if other forms of the drug like liquids or dissolvable tablets are used. Patients should follow the instructions provided with the medicine to determine the right amount.
Children under four should never use phenylephrine for nasal decongestion. Physicians usually don’t recommend the medication for children under the age of 12. Nevertheless, there are pediatric formulas of the drug, and children from six to 12 years of age would likely take 10 mg every four hours. Directions might be slightly different for chewable tablets, elixirs, or dissolvable strips.
Phenylephrine dosage completely changes when it is being used in hospital settings and is also different depending on the form in which it is given. For example, IM or subcutaneous injections have much higher milligram strengths than IV forms of the drug. With a condition like adult low blood pressure, the IM dose is 2-5 mg, to be repeated no more than every two hours, if needed.
In contrast, adult hypotension might be treated with a single IV bolus of 0.2 mg, every 15 minutes. The pediatric dose for this condition is 0.1 mg IM or 5-20 micrograms IV, which can also be given again in 10-15 minutes. Treatment indications for shock are approximately the same. For supraventricular tachycardia, the recommendations differ. Phenylephrine dosage for this condition in adults is 0.25-0.5 mg IV, while pediatric patients would be treated with 0.05-0.1 mg IV.
As an ophthalmic solution, directions for using the drug vary widely. The specific recommendation will depend on the strength, 2.5% or 10%, and the reason for use. Patients are advised to get specific instructions on how much to use and how often to apply this drug.
Especially in its over-the-counter form, phenylephrine is contraindicated by certain medical conditions. Patients with bipolar disorder, heart conditions, and thyroid disorders are advised to consult their doctor about whether there is a safe way to use the drug. The same caution applies to those with glaucoma, diabetes or an enlarged prostate. Medications can also interact with phenylephrine and might raise or lower dosage recommendations.
