Difference Between Drug Dose and Dosage

Although people often use dose and dosage interchangeably, these terms have very different meanings. By adding the suffix -age to the base dose, we are implying a regulated amount, a differentiation similar to the words mile and mileage.

Dose and Dosage Definitions

According to the American Medical Association (AMA) Manual of Style, the definitive guide on medical writing and style, dose and dosage each have very specific meanings.

In other words, a dose is simply an amount (think weight) of a medication that is administered at one specific time. Whereas, the dosage is the dose, or amount of drug, attached to a time-frequency. A dosage guides a drug regimen.

Units for Doses

According to the AMA, drug doses are expressed in conventional metric mass units (for example, milligrams or milligrams per kilogram) rather than in molar SI units. Moreover, certain drugs (such as insulin or heparin) may be prepared as mixtures and have no specific molecular weight, thereby precluding their expression in mass units.

Although other drug dose units such as drops (for ophthalmologic preparations), grains (for aspirin), and various apothecary system measurements (eg, teaspoonfuls, ounces, and drams) may be encountered clinically, these units generally are not used.

Using Tylenol as an Example

Different types of Tylenol (acetaminophen) come in different doses. Choice of which specific type, or dose, of Tylenol, depends on the condition being treated. Dosages also vary by the condition being treated.

Here are some different dosages of Tylenol dosages:

• For minor aches and pains, take 2 tablets of Regular Strength Tylenol (dose 325 mg each tablet) every 4 to 6 hours as needed. Do not exceed more than 10 tablets in 24 hours, and if the pain persists for more than a day or two, see a physician.
• For more severe aches and pains (like a bad headache), take 2 Extra Strength Tylenol caplets (dose 500 mg each caplet) every 6 hours as needed. Do not exceed more than 6 caplets a day. If pain persists for more than a day or two, see a physician.
• For arthritis pain, take 2 Tylenol Arthritis Pain caplets (dose 650 mg each caplet) every 8 hours as needed. Do not exceed more than 6 caplets a day.