Medicine Half Life Calculator

Drug half life explained

This medicine half life calculator requires the drug dosage (measured in mg, µg or g) and the half time (estimated in hours or minutes).

The decrease in plasma concentration is followed at 7 stages:

■ 50%;

■ 25%;

■ 5%;

■ 25%;

■ 125%;

■ 562%;

■ 0%.

The half time or life of a dose is defined as the period of time after administration, in either hours of minutes, in which the dosage reaches half of its concentration in the plasma.

Pharmacologically this is expressed as the Peak minus Through concentrations, divided by the interval.

Biologically, this means the elimination half time of the medicine and it is affected by factors such as receptor interactions or metabolic activity.

In order to produce the desired effect, the active substance needs to remain at a constant level for the duration of the treatment. Half life is used by professionals to establish dosage and administration schedule.

Substances and their half time

The following table introduces the half time of most common active substances:

References

1) Hammett-Stabler CA, Dasgupta A, eds. (2007) Therapeutic Drug Monitoring Data: A Concise Guide. 3rd ed. Washington, DC: AACC Press.

2) Garg U, Jacobs DS, Grady HJ, et al. Therapeutic drug monitoring. In: Jacobs DS, Oxley DK, Demott WR, eds. (2001) Jacobs & Demott Laboratory Test Handbook. 5th ed. Cleveland, Ohio: Lexi-Comp, Inc; 731-771.