Drug Dosage is a term used in the clinical sciences to describe the quantity of a drug that is administered to a subject at a given time. It may be expressed as an absolute dose, or in terms of a particular dosage form.
The relationship between a drug’s dose and the effect it produces is often illustrated with a dose-effect curve. This is a continuous function, and the slope of the curve is positive.
The median effective dose is the dose of a drug that produces a characteristic effect in fifty percent of subjects. A median effective dose is generally a standardized dose that is appropriate for measurements in vivo or in vitro.
Unlike a time-concentration curve, a dose-effect curve is monotonic and has a positive slope. However, this difference does not affect the meaning of the dose-effect curve.
Dose-effect curves may also have a negative slope. This indicates that more than one active agent is involved.
Dose-effect curves are commonly used to estimate drug potency. The point on the curve at which the dose is required to produce a specific degree of effect is called the asymptote.
Compared to the time-concentration curve, the slope of the dose-effect curve is constant throughout the range of testable doses. Therefore, a slope of the dose-effect curve is not necessarily invalid, although it may obscure the biological interpretation of the data.
Regardless of the slope of the dose-effect curve, there is an inverse relationship between the total clearance and the rate of elimination. For single compartment systems, this is given by Css, inversely proportional to the volume of the body.