This half life calculator determines in how much time the specified peak and through medicine characteristics will reach their half time and also the elimination constant. You can discover more on this subject below the form.

Peak concentration:*
Trough concentration:*
Time interval:*

How does this half life calculator work?

This is a health tool that helps you determine the half time of a medicine according to peak and through concentration but also the measured time interval. The two concentrations can be input in either mcg/mL or mg/mL while the time interval can be put in hours or minutes.

These three variables are then used in the half life calculator following the below formula in order to determine the intermediary elimination constant and ultimately the half time.

Half life = 0.693/(peak c - trough c)/t

What is a medicine’s half life?

This is an indicator of the period required for a substance to release half of its initial concentration, which means to have it metabolized or eliminated by normal processes. Half life also defines the rapidity of pharmacokinetic processes of the medicine in the plasma. It is symbolized by t1/2.

It is computed using the peak concentration which is obtained when the medicine is entirely distributed in the system and the through concentration obtained later on. The time interval is the time distance between the two phases.

Some of the most used active substances and their half lives:

Clonazepam 18-50 hours
Diazepam 20-100 hours
Flurazepam 0.8-4.2 days
Ibuprofen 1.3- 3 hours
Methadone 15 to 72 hours
Morphine 2-3 hours
Norepinephrine 2 minutes
Oxaliplatin 14 minutes
Paracetamol 1-4 hours
Phenytoin 12-42 hours
Salbutamol 1.6 hours
Zaleplon 1-2 hours


1) Pippenger CE. Principles of therapeutic drug monitoring. In: Wong SHY, (1985) ed. Therapeutic Drug Monitoring and Toxicology by Liquid Chromatography. Boca Raton, FL: CRC Press;

2) Moyer TP, Shaw LM. Therapeutic drugs and their management. In: Burtis C, Ashwood E, Bruns D. (2005) Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 4th ed. Philadelphia, PA: Saunders;

21 Mar, 2015 | 0 comments

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