How to Calculate Kel from Terminal Phase

Administer the pharmaceutical into the test system.

Take blood samples at regular time intervals from the test system. Record the time, in hours, at which you take each sample in a spreadsheet software program in a column titled "Time." Take blood at least three times.

Measure the drug concentration in each blood sample in nanograms per milileter. Record each concentration in the spreadsheet software in a column titled "Concentration," next to the respective time data.

Stop taking blood samples when the drug is no longer detected.

Find the natural logarithm of the drug concentrations. Use the natural logarithm, or natural log, function in the spreadsheet software program. It may be marked this way in the software program: =LN(insert cell reference here).

Plot a graph of natural logarithm of drug concentration against time. This task should produce a straight line graph with a negative gradient as the drug concentration decreases. A section at the top of the line may not be straight, but that factor is not important.

Find the gradient of the line between the last two points, known as the terminal phase, to find negative kel by using the spreadsheet software program's Slope function, =SLOPE(y-value1:y-value2,x-value1:x-value2). In that phrase, y-value 1 is the natural logarithm of the penultimate drug concentration, y-value2 is the natural logarithm of the last drug concentration, x-value1 is the penultimate time and x-value2 is the last time.

Kel is the negative slope of the terminal phase. For example if the line has a gradient of minus or negative 0.5, the kel is 0.5.