As-needed medications, also known as PRN medications, are medications taken on a short-term basis to alleviate acute symptoms such as pain, shortness of breath, anxiety, nausea, etc. PRN stands for Pro Re Nata, a Latin phrase that means "as-needed" when the circumstances require. They can be either prescribed by doctors or purchased over the counter at a pharmacy.
Unlike chronic medications, as-needed medications are used temporarily to resolve urgent medical conditions. Therefore, as-needed medications usually have faster onset of action than chronic medications. Chronic medications such as blood pressure medications are used daily or on a schedule to effectively prevent the disease progression.
As-needed medications and chronic medications can be used in the same day for the same disease provided that they have different mechanisms of action. For example, an acute gout attack treatment such as Colchicine may be used together in the same day with a chronic urate lowering therapy such as Allopurinol.
On the other hand, if as-needed and chronic medications have similar mechanisms of action, then as-needed medications may not be used many times during the day along with chronic medications. For example, an as-needed bronchodilator for shortness of breath such as Albuterol HFA (Ventolin HFA), may not be used every 4 to 6 hours throughout the day when a chronic bronchodilator such as Fluticasone/Salmeterol HFA (Advair HFA) is also used.
If Albuterol HFA, a short acting beta agonist, is used repeatedly throughout the day, it may act like the long acting beta agonist Salmeterol and thus may represent a drug duplication. It is appropriate to use Albuterol HFA one to two times in the same day along with Fluticasone/Salmeterol HFA use.
An example of as-needed medications is "Albuterol HFA (ProAir HFA, Proventil HFA, ProAir RespiClick, and Ventolin HFA) 90 mcg/inhalation: Inhale 1 to 2 puffs every 4 to 6 hours as needed for shortness of breath or wheezing".
In this example, the components of an as-needed medication include:
Drug name: Albuterol HFA Strength: 90 mcg/inhalation Formulation: Inhalation aerosol Dosage: 1 to 2 puffs Administration route: Inhalation Dosing intervals: Every 4 to 6 hours Used as needed For acute symptoms: Shortness of breath or wheezing Maximum daily dose: "1 to 2 puffs every 4 to 6 hours" means a maximum of 12 puffs in 24 hours.
If any component is not comprehensible from the prescription, patients are encouraged to clarify with doctors or pharmacists. It is important that patients take as-needed medications exactly as directed for the best therapy outcome. Here are a few tips for safe use of as-needed medications.
- Follow the doctor or package instructions regarding when and how to use as-needed medications.
- If there is a range of doses, start with the lowest dose in the range. For example, patients may inhale 1 puff of Albuterol HFA every 6 hours first, then later increase the dose to 2 puffs if needed.
- Do not exceed the maximum daily limit. Overdose may put patients at risk for severe side effects. For example, patients taking more than 12 puffs of Albuterol HFA in 24 hours are more likely to experience throat irritation, cough, arrhythmias, tremor, and sleeplessness.
- Know how long to wait between doses. Shortening dosing intervals may increase drug levels in the body leading to severe side effects.
- Contact doctors if no improvement is seen after using an as-needed medication. Patients may need to seek immediate medical attention. Alternatively, patients may need additional counseling for correct administering method or dose adjustment.
- Report to doctors increased frequency of use of as-needed medications. More frequent use of as-needed medications may indicate that the disease has advanced. In this case, doctors may need to adjust chronic medications to appropriately treat the disease.
- Do not use a chronic medication in place of an as-needed medication because it may not act fast enough to resolve acute symptoms. Additional examples of commonly used as-needed medications are shown below, along with instructions for adults.
- Nitroglycerin 0.4mg sublingual tablets (Nitrostat): Dissolve 1 tablet under the tongue as needed for acute anginal attack. Seek prompt medical attention if chest pain persists after first dose. May repeat 2 additional doses at 5-minute intervals. Do not take more than 3 doses within 15 minutes.
- Colchicine 0.6mg tablets (Colcrys): Take 2 tablets by mouth at the first sign of a gout flare followed by 1 tablet one hour later.
- Zolpidem 10mg tablets (Ambien): Take 1 tablet by mouth once daily immediately before bedtime as needed for sleep. The dosage for elderly or hepatically impaired patients is 5mg once daily immediately before bedtime as needed for sleep.
- Acetaminophen 500mg caplets (Extra Strength Tylenol): Take 2 caplets by mouth every 6 hours while symptoms of pain or fever last. Do not exceed 6 caplets in 24 hours, unless directed by a doctor.
- Hydrocodone/Acetaminophen 5mg/325mg tablets (Norco 5mg/325 mg): Take 1 or 2 tablets by mouth every 4 to 6 hours as needed for pain.
- Ibuprofen 600mg tablets: Take 1 tablet by mouth every 6 to 8 hours as needed for pain.
- Lorazepam 1mg tablets (Ativan): Take 1 tablet by mouth 2 times a day or 3 times a day as needed for anxiety.
- Sumatriptan 25mg tablets (Imitrex): Take 1 tablet by mouth at the onset of migraine. May repeat the dose after 2 hours if the headache returns. Do not exceed a total daily dose of 200 mg.
- Tizanidine 2mg capsules (Zanaflex): Take 1 tablet by mouth every 6 to 8 hours as needed for muscle spasms. Do not exceed a maximum of 3 doses in 24 hours.
- Ondansetron 8mg orally disintegrating tablets (Zofran ODT): Take 1 tablet by mouth twice a day to prevent nausea and vomiting associated with chemotherapy.
- Loperamide 2mg capsules (Imodium): Take 2 capsules by mouth for acute diarrhea, followed by 1 capsule after each unformed stool. The maximum daily dose is 16mg (8 capsules).
- Calcium Carbonate USP 500mg (Tums): Chew 2-4 tablets as heartburn symptoms occur, or as directed by a doctor.
As-needed mediations offer patients the flexibility to manage urgent medical conditions without going to the hospital or calling doctors. When as-needed medications are prescribed to patients, it is expected that patients take them exactly as directed and do not exceed the maximum daily limit or dosing intervals. However, when in doubt, it is necessary to contact doctors or pharmacists to ensure the safe use of as-needed medications.