The dose is the amount of drug taken at any one time. This can be expressed as the weight of the drug (e.g. 250 mg), the volume of drug solution (e.g. 10 mL, 2 drops), the number of dosage forms (e.g. 1 capsule, 1 suppository) or some other quantity (e.g. 2 puffs).
The dosage regimen is the frequency at which the drug doses are given. Examples include 2.5 mL twice a day, one tablet three times a day, one injection every four weeks.
The total daily dose is calculated from the dose and the number of times per day the dose is taken.
The dosage form is the physical form of a dose of the drug. Common dosage forms include tablets, capsules, creams, ointments, aerosols, and patches. Each dosage form may also have a number of specialized forms such as extended-release, buccal, dispersible and chewable tablets. The strength is the amount of drug in the dosage form or a unit of the dosage form (e.g. 500 mg capsule, 250 mg/5 mL suspension).
The route of administration is the way the dosage form is given. Common routes of administration include oral, rectal, inhalation, nasal and topical.
The optimal dosage is the dosage that gives the desired effect with minimum side effects.
There are many factors taken into consideration when deciding a dose of drug – including age of the patient, weight, sex, ethnicity, liver and kidney function and whether the patient smokes. Other medicines may also affect the drug dose.
Dosage instructions are written on the doctor’s prescription or hospital chart, and on the pharmacy label of a prescribed medicine. Dosage instructions are also found on the packaging and inserts of over-the-counter medicines.